#POSTGRES IF IN SELECT UPDATE#
When writing a data-modifying statement ( INSERT, UPDATE or DELETE) in WITH, it is usual to include a RETURNING clause. Each subquery can be a SELECT, TABLE, VALUES, INSERT, UPDATE or DELETE statement. The subqueries effectively act as temporary tables or views for the duration of the primary query. The WITH clause allows you to specify one or more subqueries that can be referenced by name in the primary query. The use of FOR NO KEY UPDATE, FOR UPDATE, FOR SHARE or FOR KEY SHARE requires UPDATE privilege as well (for at least one column of each table so selected). You must have SELECT privilege on each column used in a SELECT command. If FOR UPDATE, FOR NO KEY UPDATE, FOR SHARE or FOR KEY SHARE is specified, the SELECT statement locks the selected rows against concurrent updates. If the LIMIT (or FETCH FIRST) or OFFSET clause is specified, the SELECT statement only returns a subset of the result rows. If ORDER BY is not given, the rows are returned in whatever order the system finds fastest to produce. If the ORDER BY clause is specified, the returned rows are sorted in the specified order. (See UNION Clause, INTERSECT Clause, and EXCEPT Clause below.) Notice that DISTINCT is the default behavior here, even though ALL is the default for SELECT itself. The noise word DISTINCT can be added to explicitly specify eliminating duplicate rows. In all three cases, duplicate rows are eliminated unless ALL is specified. The EXCEPT operator returns the rows that are in the first result set but not in the second.
The INTERSECT operator returns all rows that are strictly in both result sets. The UNION operator returns all rows that are in one or both of the result sets. Using the operators UNION, INTERSECT, and EXCEPT, the output of more than one SELECT statement can be combined to form a single result set. SELECT ALL (the default) will return all candidate rows, including duplicates.
SELECT DISTINCT ON eliminates rows that match on all the specified expressions. SELECT DISTINCT eliminates duplicate rows from the result. The actual output rows are computed using the SELECT output expressions for each selected row or row group. (See GROUP BY Clause and HAVING Clause below.) If the HAVING clause is present, it eliminates groups that do not satisfy the given condition. If the GROUP BY clause is specified, or if there are aggregate function calls, the output is combined into groups of rows that match on one or more values, and the results of aggregate functions are computed. If the WHERE clause is specified, all rows that do not satisfy the condition are eliminated from the output. (Each element in the FROM list is a real or virtual table.) If more than one element is specified in the FROM list, they are cross-joined together. (See WITH Clause below.)Īll elements in the FROM list are computed. A WITH query that is referenced more than once in FROM is computed only once, unless specified otherwise with NOT MATERIALIZED. These effectively serve as temporary tables that can be referenced in the FROM list. SET cycle_mark_col_name USING cycle_path_col_name ]Īll queries in the WITH list are computed. WHERE CASE WHEN x 0 THEN y/x > 1.With_query ]
For example, this is a possible way of avoiding a division-by-zero failure: The example above can be written using the simple CASE syntax:Ī CASE expression does not evaluate any subexpressions that are not needed to determine the result. This is similar to the switch statement in C. If no match is found, the result of the ELSE clause (or a null value) is returned. The first expression is computed, then compared to each of the value expressions in the WHEN clauses until one is found that is equal to it. There is a “ simple” form of CASE expression that is a variant of the general form above: The data types of all the result expressions must be convertible to a single output type. If the ELSE clause is omitted and no condition is true, the result is null. If no WHEN condition yields true, the value of the CASE expression is the result of the ELSE clause. If the condition's result is not true, any subsequent WHEN clauses are examined in the same manner. If the condition's result is true, the value of the CASE expression is the result that follows the condition, and the remainder of the CASE expression is not processed. Each condition is an expression that returns a boolean result. The SQL CASE expression is a generic conditional expression, similar to if/else statements in other programming languages:ĬASE clauses can be used wherever an expression is valid.
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