Postgresql inner join
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The USING clause is a shorthand that allows you to take advantage of the specific situation where both sides of the join use the same name for the joining column(s). A pair of rows from T1 and T2 match if the ON expression evaluates to true. The ON clause is the most general kind of join condition: it takes a Boolean value expression of the same kind as is used in a WHERE clause. Also, for each row of T2 that does not satisfy the join condition with any row in T1, a joined row with null values in the columns of T1 is added. Then, for each row in T1 that does not satisfy the join condition with any row in T2, a joined row is added with null values in columns of T2.
#Postgresql inner join full#
FULL OUTER JOINįirst, an inner join is performed. This is the converse of a left join: the result table will always have a row for each row in T2. Then, for each row in T2 that does not satisfy the join condition with any row in T1, a joined row is added with null values in columns of T1. RIGHT OUTER JOINįirst, an inner join is performed. Thus, the joined table always has at least one row for each row in T1.
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LEFT OUTER JOINįirst, an inner join is performed. However, it is supported for compatibility with older releases.įor each row R1 of T1, the joined table has a row for each row in T2 that satisfies the join condition with R1. There is no real reason to use this syntax any more, because searching descendant tables is now always the default behavior. Instead of writing ONLY before the table name, you can write * after the table name to explicitly specify that descendant tables are included. However, the reference produces only the columns that appear in the named table - any columns added in subtables are ignored. When a table reference names a table that is the parent of a table inheritance hierarchy, the table reference produces rows of not only that table but all of its descendant tables, unless the key word ONLY precedes the table name. The result of the FROM list is an intermediate virtual table that can then be subject to transformations by the WHERE, GROUP BY, and HAVING clauses and is finally the result of the overall table expression. If more than one table reference is listed in the FROM clause, the tables are cross-joined (that is, the Cartesian product of their rows is formed see below). The FROM clause derives a table from one or more other tables given in a comma-separated table reference list.įROM table_reference ]Ī table reference can be a table name (possibly schema-qualified), or a derived table such as a subquery, a JOIN construct, or complex combinations of these.