class Sequel::Database::DatasetClass

Adds an further filter to an existing filter using AND. If no filter exists an error is raised. This method is identical to filter except it expects an existing filter.

DB[:table].filter(:a).and(:b) # SELECT * FROM table WHERE a AND b

Returns a new clone of the dataset with with the given options merged. If the options changed include options in COLUMN_CHANGE_OPTS, the cached columns are deleted. This method should generally not be called directly by user code.

Returns a copy of the dataset with the SQL DISTINCT clause. The DISTINCT clause is used to remove duplicate rows from the output. If arguments are provided, uses a DISTINCT ON clause, in which case it will only be distinct on those columns, instead of all returned columns. Raises an error if arguments are given and DISTINCT ON is not supported.

DB[:items].distinct # SQL: SELECT DISTINCT * FROM items
DB[:items].order(:id).distinct(:id) # SQL: SELECT DISTINCT ON (id) * FROM items ORDER BY id

Adds an EXCEPT clause using a second dataset object. An EXCEPT compound dataset returns all rows in the current dataset that are not in the given dataset. Raises an InvalidOperation if the operation is not supported. Options:

DB[:items].except(DB[:other_items])
# SELECT * FROM (SELECT * FROM items EXCEPT SELECT * FROM other_items) AS t1
DB[:items].except(DB[:other_items], :all=>true, :from_self=>false)
# SELECT * FROM items EXCEPT ALL SELECT * FROM other_items

DB[:items].except(DB[:other_items], :alias=>:i)
# SELECT * FROM (SELECT * FROM items EXCEPT SELECT * FROM other_items) AS i

Performs the inverse of Dataset#filter. Note that if you have multiple filter conditions, this is not the same as a negation of all conditions.

DB[:items].exclude(:category => 'software')
# SELECT * FROM items WHERE (category != 'software')
DB[:items].exclude(:category => 'software', :id=>3)
# SELECT * FROM items WHERE ((category != 'software') OR (id != 3))

Inverts the given conditions and adds them to the HAVING clause.

DB[:items].select_group(:name).exclude_having{count(name) < 2}
# SELECT name FROM items GROUP BY name HAVING (count(name) >= 2)

Inverts the given conditions and adds them to the WHERE clause.

DB[:items].select_group(:name).exclude_where(:category => 'software')
# SELECT * FROM items WHERE (category != 'software')
DB[:items].select_group(:name).
  exclude_having{count(name) < 2}.
  exclude_where(:category => 'software')
# SELECT name FROM items WHERE (category != 'software')
# GROUP BY name HAVING (count(name) >= 2)

Returns a copy of the dataset with the given conditions imposed upon it. If the query already has a HAVING clause, then the conditions are imposed in the HAVING clause. If not, then they are imposed in the WHERE clause.

filter accepts the following argument types:

• Hash - list of equality/inclusion expressions

• Array - depends:

  • If first member is a string, assumes the rest of the arguments are parameters and interpolates them into the string.

  • If all members are arrays of length two, treats the same way as a hash, except it allows for duplicate keys to be specified.

  • Otherwise, treats each argument as a separate condition.

• String - taken literally

• Symbol - taken as a boolean column argument (e.g. WHERE active)

• Sequel::SQL::BooleanExpression - an existing condition expression, probably created using the Sequel expression filter DSL.

filter also takes a block, which should return one of the above argument types, and is treated the same way. This block yields a virtual row object, which is easy to use to create identifiers and functions. For more details on the virtual row support, see the "Virtual Rows" guide

If both a block and regular argument are provided, they get ANDed together.

Examples:

DB[:items].filter(:id => 3)
# SELECT * FROM items WHERE (id = 3)
DB[:items].filter('price < ?', 100)
# SELECT * FROM items WHERE price < 100

DB[:items].filter([[:id, (1,2,3)], [:id, 0..10]])
# SELECT * FROM items WHERE ((id IN (1, 2, 3)) AND ((id >= 0) AND (id <= 10)))

DB[:items].filter('price < 100')
# SELECT * FROM items WHERE price < 100

DB[:items].filter(:active)
# SELECT * FROM items WHERE :active

DB[:items].filter{price < 100}
# SELECT * FROM items WHERE (price < 100)

Multiple filter calls can be chained for scoping:

software = dataset.filter(:category => 'software').filter{price < 100}
# SELECT * FROM items WHERE ((category = 'software') AND (price < 100))

See the the "Dataset Filtering" guide for more examples and details.

Returns a cloned dataset with a :update lock style.

DB[:table].for_update # SELECT * FROM table FOR UPDATE

Returns a copy of the dataset with the source changed. If no source is given, removes all tables. If multiple sources are given, it is the same as using a CROSS JOIN (cartesian product) between all tables.

DB[:items].from # SQL: SELECT *
DB[:items].from(:blah) # SQL: SELECT * FROM blah
DB[:items].from(:blah, :foo) # SQL: SELECT * FROM blah, foo

Returns a dataset selecting from the current dataset. Supplying the :alias option controls the alias of the result.

ds = DB[:items].order(:name).select(:id, :name)
# SELECT id,name FROM items ORDER BY name
ds.from_self
# SELECT * FROM (SELECT id, name FROM items ORDER BY name) AS t1

ds.from_self(:alias=>:foo)
# SELECT * FROM (SELECT id, name FROM items ORDER BY name) AS foo

Match any of the columns to any of the patterns. The terms can be strings (which use LIKE) or regular expressions (which are only supported on MySQL and PostgreSQL). Note that the total number of pattern matches will be Array(columns).length * Array(terms).length, which could cause performance issues.

Options (all are boolean):

If both :all_columns and :all_patterns are true, all columns must match all patterns.

Examples:

dataset.grep(:a, '%test%')
# SELECT * FROM items WHERE (a LIKE '%test%')
dataset.grep([:a, :b], %w'%test% foo')
# SELECT * FROM items WHERE ((a LIKE '%test%') OR (a LIKE 'foo') OR (b LIKE '%test%') OR (b LIKE 'foo'))

dataset.grep([:a, :b], %w'%foo% %bar%', :all_patterns=>true)
# SELECT * FROM a WHERE (((a LIKE '%foo%') OR (b LIKE '%foo%')) AND ((a LIKE '%bar%') OR (b LIKE '%bar%')))

dataset.grep([:a, :b], %w'%foo% %bar%', :all_columns=>true)
# SELECT * FROM a WHERE (((a LIKE '%foo%') OR (a LIKE '%bar%')) AND ((b LIKE '%foo%') OR (b LIKE '%bar%')))

dataset.grep([:a, :b], %w'%foo% %bar%', :all_patterns=>true, :all_columns=>true)
# SELECT * FROM a WHERE ((a LIKE '%foo%') AND (b LIKE '%foo%') AND (a LIKE '%bar%') AND (b LIKE '%bar%'))

Returns a copy of the dataset with the results grouped by the value of the given columns. If a block is given, it is treated as a virtual row block, similar to filter.

DB[:items].group(:id) # SELECT * FROM items GROUP BY id
DB[:items].group(:id, :name) # SELECT * FROM items GROUP BY id, name
DB[:items].group{[a, sum(b)]} # SELECT * FROM items GROUP BY a, sum(b)

Returns a dataset grouped by the given column with count by group. Column aliases may be supplied, and will be included in the select clause. If a block is given, it is treated as a virtual row block, similar to filter.

Examples:

DB[:items].group_and_count(:name).all
# SELECT name, count(*) AS count FROM items GROUP BY name 
# => [{:name=>'a', :count=>1}, ...]
DB[:items].group_and_count(:first_name, :last_name).all
# SELECT first_name, last_name, count(*) AS count FROM items GROUP BY first_name, last_name
# => [{:first_name=>'a', :last_name=>'b', :count=>1}, ...]

DB[:items].group_and_count(:first_name___name).all
# SELECT first_name AS name, count(*) AS count FROM items GROUP BY first_name
# => [{:name=>'a', :count=>1}, ...]

DB[:items].group_and_count{substr(first_name, 1, 1).as(initial)}.all
# SELECT substr(first_name, 1, 1) AS initial, count(*) AS count FROM items GROUP BY substr(first_name, 1, 1)
# => [{:initial=>'a', :count=>1}, ...]

Alias of group

Adds the appropriate CUBE syntax to GROUP BY.

Adds the appropriate ROLLUP syntax to GROUP BY.

Returns a copy of the dataset with the HAVING conditions changed. See filter for argument types.

DB[:items].group(:sum).having(:sum=>10)
# SELECT * FROM items GROUP BY sum HAVING (sum = 10)

Adds an INTERSECT clause using a second dataset object. An INTERSECT compound dataset returns all rows in both the current dataset and the given dataset. Raises an InvalidOperation if the operation is not supported. Options:

DB[:items].intersect(DB[:other_items])
# SELECT * FROM (SELECT * FROM items INTERSECT SELECT * FROM other_items) AS t1
DB[:items].intersect(DB[:other_items], :all=>true, :from_self=>false)
# SELECT * FROM items INTERSECT ALL SELECT * FROM other_items

DB[:items].intersect(DB[:other_items], :alias=>:i)
# SELECT * FROM (SELECT * FROM items INTERSECT SELECT * FROM other_items) AS i

Inverts the current filter.

DB[:items].filter(:category => 'software').invert
# SELECT * FROM items WHERE (category != 'software')
DB[:items].filter(:category => 'software', :id=>3).invert
# SELECT * FROM items WHERE ((category != 'software') OR (id != 3))

Alias of inner_join

Returns a joined dataset. Not usually called directly, users should use the appropriate join method (e.g. join, left_join, natural_join, cross_join) which fills in the type argument.

Takes the following arguments:

• type - The type of join to do (e.g. :inner)

• table - Depends on type:

  • Dataset - a subselect is performed with an alias of tN for some value of N

  • Model (or anything responding to :table_name) - table.table_name

  • String, Symbol: table

• expr - specifies conditions, depends on type:

  • Hash, Array of two element arrays - Assumes key (1st arg) is column of joined table (unless already qualified), and value (2nd arg) is column of the last joined or primary table (or the :implicit_qualifier option). To specify multiple conditions on a single joined table column, you must use an array. Uses a JOIN with an ON clause.

  • Array - If all members of the array are symbols, considers them as columns and uses a JOIN with a USING clause. Most databases will remove duplicate columns from the result set if this is used.

  • nil - If a block is not given, doesn't use ON or USING, so the JOIN should be a NATURAL or CROSS join. If a block is given, uses an ON clause based on the block, see below.

  • Everything else - pretty much the same as a using the argument in a call to filter, so strings are considered literal, symbols specify boolean columns, and Sequel expressions can be used. Uses a JOIN with an ON clause.

• options - a hash of options, with any of the following keys:

  • :table_alias - the name of the table's alias when joining, necessary for joining to the same table more than once. No alias is used by default.

  • :implicit_qualifier - The name to use for qualifying implicit conditions. By default, the last joined or primary table is used.

• block - The block argument should only be given if a JOIN with an ON clause is used, in which case it yields the table alias/name for the table currently being joined, the table alias/name for the last joined (or first table), and an array of previous SQL::JoinClause. Unlike filter, this block is not treated as a virtual row block.

Examples:

DB[:a].join_table(:cross, :b)
# SELECT * FROM a CROSS JOIN b
DB[:a].join_table(:inner, DB[:b], :c=>d)
# SELECT * FROM a INNER JOIN (SELECT * FROM b) AS t1 ON (t1.c = a.d)

DB[:a].join_table(:left, :b___c, [:d])
# SELECT * FROM a LEFT JOIN b AS c USING (d)

DB[:a].natural_join(:b).join_table(:inner, :c) do |ta, jta, js|
  (:d.qualify(ta) > :e.qualify(jta)) & {:f.qualify(ta)=>DB.from(js.first.table).select(:g)}
end
# SELECT * FROM a NATURAL JOIN b INNER JOIN c
#   ON ((c.d > b.e) AND (c.f IN (SELECT g FROM b)))

If given an integer, the dataset will contain only the first l results. If given a range, it will contain only those at offsets within that range. If a second argument is given, it is used as an offset. To use an offset without a limit, pass nil as the first argument.

DB[:items].limit(10) # SELECT * FROM items LIMIT 10
DB[:items].limit(10, 20) # SELECT * FROM items LIMIT 10 OFFSET 20
DB[:items].limit(10...20) # SELECT * FROM items LIMIT 10 OFFSET 10
DB[:items].limit(10..20) # SELECT * FROM items LIMIT 11 OFFSET 10
DB[:items].limit(nil, 20) # SELECT * FROM items OFFSET 20

Returns a cloned dataset with the given lock style. If style is a string, it will be used directly. Otherwise, a symbol may be used for database independent locking. Currently :update is respected by most databases, and :share is supported by some.

DB[:items].lock_style('FOR SHARE') # SELECT * FROM items FOR SHARE

Returns a cloned dataset without a row_proc.

ds = DB[:items]
ds.row_proc = proc{|r| r.invert}
ds.all # => [{2=>:id}]
ds.naked.all # => [{:id=>2}]

Adds an alternate filter to an existing filter using OR. If no filter exists an Error is raised.

DB[:items].filter(:a).or(:b) # SELECT * FROM items WHERE a OR b

Returns a copy of the dataset with the order changed. If the dataset has an existing order, it is ignored and overwritten with this order. If a nil is given the returned dataset has no order. This can accept multiple arguments of varying kinds, such as SQL functions. If a block is given, it is treated as a virtual row block, similar to filter.

DB[:items].order(:name) # SELECT * FROM items ORDER BY name
DB[:items].order(:a, :b) # SELECT * FROM items ORDER BY a, b
DB[:items].order('a + b'.lit) # SELECT * FROM items ORDER BY a + b
DB[:items].order(:a + :b) # SELECT * FROM items ORDER BY (a + b)
DB[:items].order(:name.desc) # SELECT * FROM items ORDER BY name DESC
DB[:items].order(:name.asc(:nulls=>:last)) # SELECT * FROM items ORDER BY name ASC NULLS LAST
DB[:items].order{sum(name).desc} # SELECT * FROM items ORDER BY sum(name) DESC
DB[:items].order(nil) # SELECT * FROM items

Alias of order_more, for naming consistency with order_prepend.

Alias of order

Returns a copy of the dataset with the order columns added to the end of the existing order.

DB[:items].order(:a).order(:b) # SELECT * FROM items ORDER BY b
DB[:items].order(:a).order_more(:b) # SELECT * FROM items ORDER BY a, b

Returns a copy of the dataset with the order columns added to the beginning of the existing order.

DB[:items].order(:a).order(:b) # SELECT * FROM items ORDER BY b
DB[:items].order(:a).order_prepend(:b) # SELECT * FROM items ORDER BY b, a

Qualify to the given table, or first source if no table is given.

DB[:items].filter(:id=>1).qualify
# SELECT items.* FROM items WHERE (items.id = 1)
DB[:items].filter(:id=>1).qualify(:i)
# SELECT i.* FROM items WHERE (i.id = 1)

Return a copy of the dataset with unqualified identifiers in the SELECT, WHERE, GROUP, HAVING, and ORDER clauses qualified by the given table. If no columns are currently selected, select all columns of the given table.

DB[:items].filter(:id=>1).qualify_to(:i)
# SELECT i.* FROM items WHERE (i.id = 1)

Qualify the dataset to its current first source. This is useful if you have unqualified identifiers in the query that all refer to the first source, and you want to join to another table which has columns with the same name as columns in the current dataset. See qualify_to.

DB[:items].filter(:id=>1).qualify_to_first_source
# SELECT items.* FROM items WHERE (items.id = 1)

Modify the RETURNING clause, only supported on a few databases. If returning is used, instead of insert returning the autogenerated primary key or update/delete returning the number of modified rows, results are returned using fetch_rows.

DB[:items].returning # RETURNING *
DB[:items].returning(nil) # RETURNING NULL
DB[:items].returning(:id, :name) # RETURNING id, name

Returns a copy of the dataset with the order reversed. If no order is given, the existing order is inverted.

DB[:items].reverse(:id) # SELECT * FROM items ORDER BY id DESC
DB[:items].order(:id).reverse # SELECT * FROM items ORDER BY id DESC
DB[:items].order(:id).reverse(:name.asc) # SELECT * FROM items ORDER BY name ASC

Alias of reverse

Returns a copy of the dataset with the columns selected changed to the given columns. This also takes a virtual row block, similar to filter.

DB[:items].select(:a) # SELECT a FROM items
DB[:items].select(:a, :b) # SELECT a, b FROM items
DB[:items].select{[a, sum(b)]} # SELECT a, sum(b) FROM items

Returns a copy of the dataset selecting the wildcard if no arguments are given. If arguments are given, treat them as tables and select all columns (using the wildcard) from each table.

DB[:items].select(:a).select_all # SELECT * FROM items
DB[:items].select_all(:items) # SELECT items.* FROM items
DB[:items].select_all(:items, :foo) # SELECT items.*, foo.* FROM items

Returns a copy of the dataset with the given columns added to the existing selected columns. If no columns are currently selected, it will select the columns given in addition to *.

DB[:items].select(:a).select(:b) # SELECT b FROM items
DB[:items].select(:a).select_append(:b) # SELECT a, b FROM items
DB[:items].select_append(:b) # SELECT *, b FROM items

Set both the select and group clauses with the given columns. Column aliases may be supplied, and will be included in the select clause. This also takes a virtual row block similar to filter.

DB[:items].select_group(:a, :b)
# SELECT a, b FROM items GROUP BY a, b
DB[:items].select_group(:c___a){f(c2)}
# SELECT c AS a, f(c2) FROM items GROUP BY c, f(c2)

Returns a copy of the dataset with the given columns added to the existing selected columns. If no columns are currently selected it will just select the columns given.

DB[:items].select(:a).select(:b) # SELECT b FROM items
DB[:items].select(:a).select_more(:b) # SELECT a, b FROM items
DB[:items].select_more(:b) # SELECT b FROM items

Set the server for this dataset to use. Used to pick a specific database shard to run a query against, or to override the default (where SELECT uses :read_only database and all other queries use the :default database). This method is always available but is only useful when database sharding is being used.

DB[:items].all # Uses the :read_only or :default server 
DB[:items].delete # Uses the :default server
DB[:items].server(:blah).delete # Uses the :blah server

Set the default values for insert and update statements. The values hash passed to insert or update are merged into this hash, so any values in the hash passed to insert or update will override values passed to this method.

DB[:items].set_defaults(:a=>'a', :c=>'c').insert(:a=>'d', :b=>'b')
# INSERT INTO items (a, c, b) VALUES ('d', 'c', 'b')

Set values that override hash arguments given to insert and update statements. This hash is merged into the hash provided to insert or update, so values will override any values given in the insert/update hashes.

DB[:items].set_overrides(:a=>'a', :c=>'c').insert(:a=>'d', :b=>'b')
# INSERT INTO items (a, c, b) VALUES ('a', 'c', 'b')

Unbind bound variables from this dataset's filter and return an array of two objects. The first object is a modified dataset where the filter has been replaced with one that uses bound variable placeholders. The second object is the hash of unbound variables. You can then prepare and execute (or just call) the dataset with the bound variables to get results.

ds, bv = DB[:items].filter(:a=>1).unbind
ds # SELECT * FROM items WHERE (a = $a)
bv #  {:a => 1}
ds.call(:select, bv)

Returns a copy of the dataset with no filters (HAVING or WHERE clause) applied.

DB[:items].group(:a).having(:a=>1).where(:b).unfiltered
# SELECT * FROM items GROUP BY a

Returns a copy of the dataset with no grouping (GROUP or HAVING clause) applied.

DB[:items].group(:a).having(:a=>1).where(:b).ungrouped
# SELECT * FROM items WHERE b

Adds a UNION clause using a second dataset object. A UNION compound dataset returns all rows in either the current dataset or the given dataset. Options:

DB[:items].union(DB[:other_items])
# SELECT * FROM (SELECT * FROM items UNION SELECT * FROM other_items) AS t1
DB[:items].union(DB[:other_items], :all=>true, :from_self=>false)
# SELECT * FROM items UNION ALL SELECT * FROM other_items

DB[:items].union(DB[:other_items], :alias=>:i)
# SELECT * FROM (SELECT * FROM items UNION SELECT * FROM other_items) AS i

Returns a copy of the dataset with no limit or offset.

DB[:items].limit(10, 20).unlimited # SELECT * FROM items

Returns a copy of the dataset with no order.

DB[:items].order(:a).unordered # SELECT * FROM items

Add a condition to the WHERE clause. See filter for argument types.

DB[:items].group(:a).having(:a).filter(:b)
# SELECT * FROM items GROUP BY a HAVING a AND b
DB[:items].group(:a).having(:a).where(:b)
# SELECT * FROM items WHERE b GROUP BY a HAVING a

Add a common table expression (CTE) with the given name and a dataset that defines the CTE. A common table expression acts as an inline view for the query. Options:

DB[:items].with(:items, DB[:syx].filter(:name.like('A%')))
# WITH items AS (SELECT * FROM syx WHERE (name LIKE 'A%')) SELECT * FROM items

Add a recursive common table expression (CTE) with the given name, a dataset that defines the nonrecursive part of the CTE, and a dataset that defines the recursive part of the CTE. Options:

DB[:t].select(:i___id, :pi___parent_id).
 with_recursive(:t,
                DB[:i1].filter(:parent_id=>nil),
                DB[:t].join(:t, :i=>:parent_id).select(:i1__id, :i1__parent_id),
                :args=>[:i, :pi])
# WITH RECURSIVE t(i, pi) AS (
#   SELECT * FROM i1 WHERE (parent_id IS NULL)
#   UNION ALL
#   SELECT i1.id, i1.parent_id FROM t INNER JOIN t ON (t.i = t.parent_id)
# )
# SELECT i AS id, pi AS parent_id FROM t

Returns a copy of the dataset with the static SQL used. This is useful if you want to keep the same row_proc/graph, but change the SQL used to custom SQL.

DB[:items].with_sql('SELECT * FROM foo') # SELECT * FROM foo

You can use placeholders in your SQL and provide arguments for those placeholders:

DB[:items].with_sql('SELECT ? FROM foo', 1) # SELECT 1 FROM foo

You can also provide a method name and arguments to call to get the SQL:

DB[:items].with_sql(:insert_sql, :b=>1) # INSERT INTO items (b) VALUES (1)

Inserts the given argument into the database. Returns self so it can be used safely when chaining:

DB[:items] << {:id=>0, :name=>'Zero'} << DB[:old_items].select(:id, name)

Returns the first record matching the conditions. Examples:

DB[:table][:id=>1] # SELECT * FROM table WHERE (id = 1) LIMIT 1
# => {:id=1}

Update all records matching the conditions with the values specified. Returns the number of rows affected.

DB[:table][:id=>1] = {:id=>2} # UPDATE table SET id = 2 WHERE id = 1
# => 1 # number of rows affected

Returns an array with all records in the dataset. If a block is given, the array is iterated over after all items have been loaded.

DB[:table].all # SELECT * FROM table
# => [{:id=>1, ...}, {:id=>2, ...}, ...]
# Iterate over all rows in the table
DB[:table].all{|row| p row}

Returns the average value for the given column.

DB[:table].avg(:number) # SELECT avg(number) FROM table LIMIT 1
# => 3

Returns the columns in the result set in order as an array of symbols. If the columns are currently cached, returns the cached value. Otherwise, a SELECT query is performed to retrieve a single row in order to get the columns.

If you are looking for all columns for a single table and maybe some information about each column (e.g. database type), see Database#schema.

DB[:table].columns
# => [:id, :name]

Ignore any cached column information and perform a query to retrieve a row in order to get the columns.

DB[:table].columns!
# => [:id, :name]

Returns the number of records in the dataset.

DB[:table].count # SELECT COUNT(*) AS count FROM table LIMIT 1
# => 3

Deletes the records in the dataset. The returned value should be number of records deleted, but that is adapter dependent.

DB[:table].delete # DELETE * FROM table
# => 3

Iterates over the records in the dataset as they are yielded from the database adapter, and returns self.

DB[:table].each{|row| p row} # SELECT * FROM table

Note that this method is not safe to use on many adapters if you are running additional queries inside the provided block. If you are running queries inside the block, you should use all instead of each for the outer queries, or use a separate thread or shard inside each:

Returns true if no records exist in the dataset, false otherwise

DB[:table].empty? # SELECT 1 AS one FROM table LIMIT 1
# => false

Executes a select query and fetches records, yielding each record to the supplied block. The yielded records should be hashes with symbol keys. This method should probably should not be called by user code, use each instead.

If a integer argument is given, it is interpreted as a limit, and then returns all matching records up to that limit. If no argument is passed, it returns the first matching record. If any other type of argument(s) is passed, it is given to filter and the first matching record is returned. If a block is given, it is used to filter the dataset before returning anything. Examples:

DB[:table].first # SELECT * FROM table LIMIT 1
# => {:id=>7}
DB[:table].first(2) # SELECT * FROM table LIMIT 2
# => [{:id=>6}, {:id=>4}]

DB[:table].first(:id=>2) # SELECT * FROM table WHERE (id = 2) LIMIT 1
# => {:id=>2}

DB[:table].first("id = 3") # SELECT * FROM table WHERE (id = 3) LIMIT 1
# => {:id=>3}

DB[:table].first("id = ?", 4) # SELECT * FROM table WHERE (id = 4) LIMIT 1
# => {:id=>4}

DB[:table].first{id > 2} # SELECT * FROM table WHERE (id > 2) LIMIT 1
# => {:id=>5}

DB[:table].first("id > ?", 4){id < 6} # SELECT * FROM table WHERE ((id > 4) AND (id < 6)) LIMIT 1
# => {:id=>5}

DB[:table].first(2){id < 2} # SELECT * FROM table WHERE (id < 2) LIMIT 2
# => [{:id=>1}]

Return the column value for the first matching record in the dataset. Raises an error if both an argument and block is given.

DB[:table].get(:id) # SELECT id FROM table LIMIT 1
# => 3
ds.get{sum(id)} # SELECT sum(id) FROM table LIMIT 1
# => 6

Inserts multiple records into the associated table. This method can be used to efficiently insert a large number of records into a table in a single query if the database supports it. Inserts are automatically wrapped in a transaction.

This method is called with a columns array and an array of value arrays:

DB[:table].import([:x, :y], [[1, 2], [3, 4]])
# INSERT INTO table (x, y) VALUES (1, 2) 
# INSERT INTO table (x, y) VALUES (3, 4)

This method also accepts a dataset instead of an array of value arrays:

DB[:table].import([:x, :y], DB[:table2].select(:a, :b))
# INSERT INTO table (x, y) SELECT a, b FROM table2

Options:

Inserts values into the associated table. The returned value is generally the value of the primary key for the inserted row, but that is adapter dependent.

insert handles a number of different argument formats:

Examples:

DB[:items].insert
# INSERT INTO items DEFAULT VALUES
DB[:items].insert({})
# INSERT INTO items DEFAULT VALUES

DB[:items].insert([1,2,3])
# INSERT INTO items VALUES (1, 2, 3)

DB[:items].insert([:a, :b], [1,2])
# INSERT INTO items (a, b) VALUES (1, 2)

DB[:items].insert(:a => 1, :b => 2)
# INSERT INTO items (a, b) VALUES (1, 2)

DB[:items].insert(DB[:old_items])
# INSERT INTO items SELECT * FROM old_items

DB[:items].insert([:a, :b], DB[:old_items])
# INSERT INTO items (a, b) SELECT * FROM old_items

Inserts multiple values. If a block is given it is invoked for each item in the given array before inserting it. See multi_insert as a possibly faster version that may be able to insert multiple records in one SQL statement (if supported by the database). Returns an array of primary keys of inserted rows.

DB[:table].insert_multiple([{:x=>1}, {:x=>2}])
# => [4, 5]
# INSERT INTO table (x) VALUES (1)
# INSERT INTO table (x) VALUES (2)
DB[:table].insert_multiple([{:x=>1}, {:x=>2}]){|row| row[:y] = row[:x] * 2}
# => [6, 7]
# INSERT INTO table (x, y) VALUES (1, 2)
# INSERT INTO table (x, y) VALUES (2, 4)

Returns the interval between minimum and maximum values for the given column.

DB[:table].interval(:id) # SELECT (max(id) - min(id)) FROM table LIMIT 1
# => 6

Reverses the order and then runs first with the given arguments and block. Note that this will not necessarily give you the last record in the dataset, unless you have an unambiguous order. If there is not currently an order for this dataset, raises an Error.

DB[:table].order(:id).last # SELECT * FROM table ORDER BY id DESC LIMIT 1
# => {:id=>10}
DB[:table].order(:id.desc).last(2) # SELECT * FROM table ORDER BY id ASC LIMIT 2
# => [{:id=>1}, {:id=>2}]

Maps column values for each record in the dataset (if a column name is given), or performs the stock mapping functionality of Enumerable otherwise. Raises an Error if both an argument and block are given.

DB[:table].map(:id) # SELECT * FROM table
# => [1, 2, 3, ...]
DB[:table].map{|r| r[:id] * 2} # SELECT * FROM table
# => [2, 4, 6, ...]

You can also provide an array of column names:

DB[:table].map([:id, :name]) # SELECT * FROM table
# => [[1, 'A'], [2, 'B'], [3, 'C'], ...]

Returns the maximum value for the given column.

DB[:table].max(:id) # SELECT max(id) FROM table LIMIT 1
# => 10

Returns the minimum value for the given column.

DB[:table].min(:id) # SELECT min(id) FROM table LIMIT 1
# => 1

This is a front end for import that allows you to submit an array of hashes instead of arrays of columns and values:

DB[:table].multi_insert([{:x => 1}, {:x => 2}])
# INSERT INTO table (x) VALUES (1)
# INSERT INTO table (x) VALUES (2)

Be aware that all hashes should have the same keys if you use this calling method, otherwise some columns could be missed or set to null instead of to default values.

This respects the same options as import.

Returns a Range instance made from the minimum and maximum values for the given column.

DB[:table].range(:id) # SELECT max(id) AS v1, min(id) AS v2 FROM table LIMIT 1
# => 1..10

Returns a hash with key_column values as keys and value_column values as values. Similar to to_hash, but only selects the columns given.

DB[:table].select_hash(:id, :name) # SELECT id, name FROM table
# => {1=>'a', 2=>'b', ...}

You can also provide an array of column names for either the key_column, the value column, or both:

DB[:table].select_hash([:id, :foo], [:name, :bar]) # SELECT * FROM table
# {[1, 3]=>['a', 'c'], [2, 4]=>['b', 'd'], ...}

When using this method, you must be sure that each expression has an alias that Sequel can determine. Usually you can do this by calling the as method on the expression and providing an alias.

Returns a hash with key_column values as keys and an array of value_column values. Similar to to_hash_groups, but only selects the columns given.

DB[:table].select_hash(:name, :id) # SELECT id, name FROM table
# => {'a'=>[1, 4, ...], 'b'=>[2, ...], ...}

You can also provide an array of column names for either the key_column, the value column, or both:

DB[:table].select_hash([:first, :middle], [:last, :id]) # SELECT * FROM table
# {['a', 'b']=>[['c', 1], ['d', 2], ...], ...}

When using this method, you must be sure that each expression has an alias that Sequel can determine. Usually you can do this by calling the as method on the expression and providing an alias.

Selects the column given (either as an argument or as a block), and returns an array of all values of that column in the dataset. If you give a block argument that returns an array with multiple entries, the contents of the resulting array are undefined. Raises an Error if called with both an argument and a block.

DB[:table].select_map(:id) # SELECT id FROM table
# => [3, 5, 8, 1, ...]
DB[:table].select_map{id * 2} # SELECT (id * 2) FROM table
# => [6, 10, 16, 2, ...]

You can also provide an array of column names:

DB[:table].select_map([:id, :name]) # SELECT id, name FROM table
# => [[1, 'A'], [2, 'B'], [3, 'C'], ...]

If you provide an array of expressions, you must be sure that each entry in the array has an alias that Sequel can determine. Usually you can do this by calling the as method on the expression and providing an alias.

The same as select_map, but in addition orders the array by the column.

DB[:table].select_order_map(:id) # SELECT id FROM table ORDER BY id
# => [1, 2, 3, 4, ...]
DB[:table].select_order_map{id * 2} # SELECT (id * 2) FROM table ORDER BY (id * 2)
# => [2, 4, 6, 8, ...]

You can also provide an array of column names:

DB[:table].select_order_map([:id, :name]) # SELECT id, name FROM table ORDER BY id, name
# => [[1, 'A'], [2, 'B'], [3, 'C'], ...]

If you provide an array of expressions, you must be sure that each entry in the array has an alias that Sequel can determine. Usually you can do this by calling the as method on the expression and providing an alias.

Alias for update, but not aliased directly so subclasses don't have to override both methods.

Returns the first record in the dataset, or nil if the dataset has no records. Users should probably use first instead of this method.

Returns the first value of the first record in the dataset. Returns nil if dataset is empty. Users should generally use get instead of this method.

Returns the sum for the given column.

DB[:table].sum(:id) # SELECT sum(id) FROM table LIMIT 1
# => 55

Returns a string in CSV format containing the dataset records. By default the CSV representation includes the column titles in the first line. You can turn that off by passing false as the include_column_titles argument.

This does not use a CSV library or handle quoting of values in any way. If any values in any of the rows could include commas or line endings, you shouldn't use this.

puts DB[:table].to_csv # SELECT * FROM table
# id,name
# 1,Jim
# 2,Bob

Returns a hash with one column used as key and another used as value. If rows have duplicate values for the key column, the latter row(s) will overwrite the value of the previous row(s). If the value_column is not given or nil, uses the entire hash as the value.

DB[:table].to_hash(:id, :name) # SELECT * FROM table
# {1=>'Jim', 2=>'Bob', ...}
DB[:table].to_hash(:id) # SELECT * FROM table
# {1=>{:id=>1, :name=>'Jim'}, 2=>{:id=>2, :name=>'Bob'}, ...}

You can also provide an array of column names for either the key_column, the value column, or both:

DB[:table].to_hash([:id, :foo], [:name, :bar]) # SELECT * FROM table
# {[1, 3]=>['Jim', 'bo'], [2, 4]=>['Bob', 'be'], ...}
DB[:table].to_hash([:id, :name]) # SELECT * FROM table
# {[1, 'Jim']=>{:id=>1, :name=>'Jim'}, [2, 'Bob'=>{:id=>2, :name=>'Bob'}, ...}

Returns a hash with one column used as key and the values being an array of column values. If the value_column is not given or nil, uses the entire hash as the value.

DB[:table].to_hash(:name, :id) # SELECT * FROM table
# {'Jim'=>[1, 4, 16, ...], 'Bob'=>[2], ...}
DB[:table].to_hash(:name) # SELECT * FROM table
# {'Jim'=>[{:id=>1, :name=>'Jim'}, {:id=>4, :name=>'Jim'}, ...], 'Bob'=>[{:id=>2, :name=>'Bob'}], ...}

You can also provide an array of column names for either the key_column, the value column, or both:

DB[:table].to_hash([:first, :middle], [:last, :id]) # SELECT * FROM table
# {['Jim', 'Bob']=>[['Smith', 1], ['Jackson', 4], ...], ...}
DB[:table].to_hash([:first, :middle]) # SELECT * FROM table
# {['Jim', 'Bob']=>[{:id=>1, :first=>'Jim', :middle=>'Bob', :last=>'Smith'}, ...], ...}

Truncates the dataset. Returns nil.

DB[:table].truncate # TRUNCATE table
# => nil

Updates values for the dataset. The returned value is generally the number of rows updated, but that is adapter dependent. values should a hash where the keys are columns to set and values are the values to which to set the columns.

DB[:table].update(:x=>nil) # UPDATE table SET x = NULL
# => 10
DB[:table].update(:x=>:x+1, :y=>0) # UPDATE table SET x = (x + 1), y = 0
# => 10

Execute the given SQL and return the number of rows deleted. This exists solely as an optimization, replacing with_sql(sql).delete. It's significantly faster as it does not require cloning the current dataset.

Returns a DELETE SQL query string. See delete.

dataset.filter{|o| o.price >= 100}.delete_sql
# => "DELETE FROM items WHERE (price >= 100)"

Returns an EXISTS clause for the dataset as a LiteralString.

DB.select(1).where(DB[:items].exists)
# SELECT 1 WHERE (EXISTS (SELECT * FROM items))

Returns an INSERT SQL query string. See insert.

DB[:items].insert_sql(:a=>1)
# => "INSERT INTO items (a) VALUES (1)"

Returns a literal representation of a value to be used as part of an SQL expression.

DB[:items].literal("abc'def\\") #=> "'abc''def\\\\'"
DB[:items].literal(:items__id) #=> "items.id"
DB[:items].literal([1, 2, 3]) => "(1, 2, 3)"
DB[:items].literal(DB[:items]) => "(SELECT * FROM items)"
DB[:items].literal(:x + 1 > :y) => "((x + 1) > y)"

If an unsupported object is given, an Error is raised.

Returns an array of insert statements for inserting multiple records. This method is used by multi_insert to format insert statements and expects a keys array and and an array of value arrays.

This method should be overridden by descendants if the support inserting multiple records in a single SQL statement.

Returns a SELECT SQL query string.

dataset.select_sql # => "SELECT * FROM items"

Same as select_sql, not aliased directly to make subclassing simpler.

Returns a TRUNCATE SQL query string. See truncate

DB[:items].truncate_sql # => 'TRUNCATE items'

Formats an UPDATE statement using the given values. See update.

DB[:items].update_sql(:price => 100, :category => 'software')
# => "UPDATE items SET price = 100, category = 'software'

Raises an Error if the dataset is grouped or includes more than one table.

Whether this dataset will provide accurate number of rows matched for delete and update statements. Accurate in this case is the number of rows matched by the dataset's filter.

Whether this dataset quotes identifiers.

Whether you must use a column alias list for recursive CTEs (false by default).

Whether type specifiers are required for prepared statement/bound variable argument placeholders (i.e. :bv__integer)

Whether the dataset requires SQL standard datetimes (false by default, as most allow strings with ISO 8601 format).

Whether the dataset supports common table expressions (the WITH clause). If given, type can be :select, :insert, :update, or :delete, in which case it determines whether WITH is supported for the respective statement type.

Whether the dataset supports common table expressions (the WITH clause) in subqueries. If false, applies the WITH clause to the main query, which can cause issues if multiple WITH clauses use the same name.

Whether the dataset supports or can emulate the DISTINCT ON clause, false by default.

Whether the dataset supports CUBE with GROUP BY.

Whether the dataset supports ROLLUP with GROUP BY.

Whether this dataset supports the insert_select method for returning all columns values directly from an insert query.

Whether the dataset supports the INTERSECT and EXCEPT compound operations, true by default.

Whether the dataset supports the INTERSECT ALL and EXCEPT ALL compound operations, true by default.

Whether the dataset supports the IS TRUE syntax.

Whether the dataset supports the JOIN table USING (column1, ...) syntax.

Whether modifying joined datasets is supported.

Whether the IN/NOT IN operators support multiple columns when an array of values is given.

Whether the dataset supports or can fully emulate the DISTINCT ON clause, including respecting the ORDER BY clause, false by default

Whether the RETURNING clause is supported for the given type of query. type can be :insert, :update, or :delete.

Whether the database supports SELECT *, column FROM table

Whether the dataset supports timezones in literal timestamps

Whether the dataset supports fractional seconds in literal timestamps

Whether the dataset supports WHERE TRUE (or WHERE 1 for databases that that use 1 for true).

Whether the dataset supports window functions.

Adds the given graph aliases to the list of graph aliases to use, unlike set_graph_aliases, which replaces the list (the equivalent of select_more when graphing). See set_graph_aliases.

DB[:table].add_graph_aliases(:some_alias=>[:table, :column])
# SELECT ..., table.column AS some_alias
# => {:table=>{:column=>some_alias_value, ...}, ...}

Allows you to join multiple datasets/tables and have the result set split into component tables.

This differs from the usual usage of join, which returns the result set as a single hash. For example:

# CREATE TABLE artists (id INTEGER, name TEXT);
# CREATE TABLE albums (id INTEGER, name TEXT, artist_id INTEGER);
DB[:artists].left_outer_join(:albums, :artist_id=>:id).first
#=> {:id=>albums.id, :name=>albums.name, :artist_id=>albums.artist_id}

DB[:artists].graph(:albums, :artist_id=>:id).first
#=> {:artists=>{:id=>artists.id, :name=>artists.name}, :albums=>{:id=>albums.id, :name=>albums.name, :artist_id=>albums.artist_id}}

Using a join such as left_outer_join, the attribute names that are shared between the tables are combined in the single return hash. You can get around that by using select with correct aliases for all of the columns, but it is simpler to use graph and have the result set split for you. In addition, graph respects any row_proc of the current dataset and the datasets you use with graph.

If you are graphing a table and all columns for that table are nil, this indicates that no matching rows existed in the table, so graph will return nil instead of a hash with all nil values:

# If the artist doesn't have any albums
DB[:artists].graph(:albums, :artist_id=>:id).first
=> {:artists=>{:id=>artists.id, :name=>artists.name}, :albums=>nil}

Arguments:

Options:

This allows you to manually specify the graph aliases to use when using graph. You can use it to only select certain columns, and have those columns mapped to specific aliases in the result set. This is the equivalent of select for a graphed dataset, and must be used instead of select whenever graphing is used.

DB[:artists].graph(:albums, :artist_id=>:id).
  set_graph_aliases(:name=>:artists,
                    :album_name=>[:albums, :name],
                    :forty_two=>[:albums, :fourtwo, 42]).first
# SELECT artists.name, albums.name AS album_name, 42 AS forty_two ...
# => {:artists=>{:name=>artists.name}, :albums=>{:name=>albums.name, :fourtwo=>42}}

Remove the splitting of results into subhashes, and all metadata related to the current graph (if any).

Define a hash value such that datasets with the same DB, opts, and SQL will be consider equal.

Yield a dataset for each server in the connection pool that is tied to that server. Intended for use in sharded environments where all servers need to be modified with the same data:

DB[:configs].where(:key=>'setting').each_server{|ds| ds.update(:value=>'new_value')}

Alias for ==

Alias of first_source_alias

The first source (primary table) for this dataset. If the dataset doesn't have a table, raises an Error. If the table is aliased, returns the aliased name.

DB[:table].first_source_alias
# => :table
DB[:table___t].first_source_alias
# => :t

The first source (primary table) for this dataset. If the dataset doesn't have a table, raises an error. If the table is aliased, returns the original table, not the alias

DB[:table].first_source_table
# => :table
DB[:table___t].first_source_table
# => :table

Define a hash value such that datasets with the same DB, opts, and SQL will have the same hash value

The String instance method to call on identifiers before sending them to the database.

The String instance method to call on identifiers before sending them to the database.

Returns a string representation of the dataset including the class name and the corresponding SQL select statement.

The alias to use for the row_number column, used when emulating OFFSET support and for eager limit strategies

Splits a possible implicit alias in c, handling both SQL::AliasedExpressions and Symbols. Returns an array of two elements, with the first being the main expression, and the second being the alias.

Creates a unique table alias that hasn't already been used in the dataset. table_alias can be any type of object accepted by alias_symbol. The symbol returned will be the implicit alias in the argument, possibly appended with "_N" if the implicit alias has already been used, where N is an integer starting at 0 and increasing until an unused one is found.

You can provide a second addition array argument containing symbols that should not be considered valid table aliases. The current aliases for the FROM and JOIN tables are automatically included in this array.

DB[:table].unused_table_alias(:t)
# => :t
DB[:table].unused_table_alias(:table)
# => :table_0

DB[:table, :table_0].unused_table_alias(:table)
# => :table_1

DB[:table, :table_0].unused_table_alias(:table, [:table_1, :table_2])
# => :table_3

Add a mutation method to this dataset instance.

Remove the row_proc from the current dataset.

Set the bind variables to use for the call. If bind variables have already been set for this dataset, they are updated with the contents of bind_vars.

DB[:table].filter(:id=>:$id).bind(:id=>1).call(:first)
# SELECT * FROM table WHERE id = ? LIMIT 1 -- (1)
# => {:id=>1}

For the given type (:select, :first, :insert, :insert_select, :update, or :delete), run the sql with the bind variables specified in the hash. values is a hash passed to insert or update (if one of those types is used), which may contain placeholders.

DB[:table].filter(:id=>:$id).call(:first, :id=>1)
# SELECT * FROM table WHERE id = ? LIMIT 1 -- (1)
# => {:id=>1}

Prepare an SQL statement for later execution. Takes a type similar to call, and the name symbol of the prepared statement. While name defaults to nil, it should always be provided as a symbol for the name of the prepared statement, as some databases require that prepared statements have names.

This returns a clone of the dataset extended with PreparedStatementMethods, which you can call with the hash of bind variables to use. The prepared statement is also stored in the associated database, where it can be called by name. The following usage is identical:

ps = DB[:table].filter(:name=>:$name).prepare(:first, :select_by_name)
ps.call(:name=>'Blah')
# SELECT * FROM table WHERE name = ? -- ('Blah')
# => {:id=>1, :name=>'Blah'}

DB.call(:select_by_name, :name=>'Blah') # Same thing

SQL fragment for AliasedExpression

SQL fragment for Array

SQL fragment for BooleanConstants

SQL fragment for CaseExpression

SQL fragment for the SQL CAST expression

SQL fragment for specifying all columns in a given table

SQL fragment for the complex expression.