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How to execute a subquery in PostgreSQL?
PostgreSQL executes the query that contains a subquery in the following sequence: 1 First, executes the subquery. 2 Second, gets the result and passes it to the outer query. 3 Third, executes the outer query. More
Which is the outer query in PostgreSQL?
The query that contains the subquery is known as an outer query. PostgreSQL executes the query that contains a subquery in the following sequence: First, executes the subquery. Second, gets the result and passes it to the outer query.
When to use the exists operator in PostgreSQL?
If the subquery returns any row, the EXISTS operator returns true. If the subquery returns no row, the result of EXISTS operator is false. The EXISTS operator only cares about the number of rows returned from the subquery, not the content of the rows, therefore, the common coding convention of EXISTS operator is as follows:
When to use subquery in the where clause?
A subquery can return zero or more rows. To use this subquery, you use the IN operator in the WHERE clause. For example, to get films that have the returned date between 2005-05-29 and 2005-05-30, you use the following query: It returns multiple rows so we can use this query as a subquery in the WHERE clause of a query as follows:
How is a SELECT query processed in PostgreSQL?
The general processing of SELECT is as follows: All queries in the WITH list are computed. These effectively serve as temporary tables that can be referenced in the FROM list. A WITH query that is referenced more than once in FROM is computed only once. (See WITH Clause below.) All elements in the FROM list are computed.
How are column names specified in PostgreSQL select?
A name (without schema qualification) must be specified for each WITH query. Optionally, a list of column names can be specified; if this is omitted, the column names are inferred from the subquery. If RECURSIVE is specified, it allows a SELECT subquery to reference itself by name.