We can use it pretty much anywhere a valid expression can be used.įor example, we can use the CASE operator as part of an UPDATE statement when updating data in a database. The CASE operator isn’t limited to just SELECT statements. Using the CASE Operator in Other Contexts That’s because I set up psql to return that string for NULL values. In my case, NULL values are represented by the string. Let’s omit the ELSE clause from the first example: SELECT If we omit the ELSE clause, and none of the conditions are met, the result is NULL. The above examples use the ELSE clause to determine what happens if none of the conditions are met, however, the ELSE clause is optional. Since CASE is an expression, you can use it in any places where an expression can be used e.g., SELECT, WHERE, GROUP BY, and HAVING clause. In Postgresql, we can return nothing or null when using the if-else statement, which means when the expression will true, then it returns the value otherwise returns nothing.
It allows you to add if-else logic to the query to form a powerful query.
Its good for displaying a value in the SELECT query based on logic that. If a true expression is not found, will return the ELSE statement, if present. The PostgreSQL CASE expression is the same as IF/ELSE statement in other programming languages. The CASE statement allows you to perform an IF-THEN-ELSE check within an SQL statement. We could rewrite this to a searched CASE expression if we wanted. Evaluates a list of conditions and returns the first resulting true expression. Here’s an example to demonstrate the simple CASE expression: SELECT If the condition evaluates to false, the expression after ELSE is returned, or NULL. The searched CASE expression evaluates a set of Boolean expressions to determine the result. If the condition evaluates to true, the expression after THEN is returned. The other option is the searched CASE expression: CASE The simple CASE expression compares an expression to a set of simple expressions to determine the result. One form is the simple CASE expression: CASE value The basic syntax for the CASE expression goes like this: CASE WHEN condition THEN resultĪctually, there are two forms of CASE expression. The CASE expression is included in the SQL standard (ISO/IEC 9075), and most major RDBMSs support it. To be absolutely sure, write-lock the table in the same transaction before proceeding as demonstrated.In PostgreSQL, the CASE expression compares a list of conditions and returns one of multiple possible result expressions. Though unlikely, concurrent transactions writing to the same table may interfere. This is equivalent and much faster, though: IF EXISTS (SELECT FROM orders).
Or: IF (SELECT count(*) > 0 FROM orders). If statements are not actually part of the SQL Spec (The supported version of PostgreSQL 9.5 onwards supports most of the 2011 spec), and so in order to. The IF statement is part of the default procedural language PL/pgSQL. You need END IF at the end of the IF statement.Ī sub-select must be surrounded by parentheses: IF (SELECT count(*) FROM orders) > 0. 4 Answers Sorted by: 210 DO do BEGIN IF EXISTS (SELECT FROM orders) THEN DELETE FROM orders ELSE INSERT INTO orders VALUES (1,2,3) END IF END do There are no procedural elements in standard SQL. You need a semicolon ( ) at the end of each statement in plpgsql ( except for the final END). You need to create a function or execute an ad-hoc statement with the DO command. There are no procedural elements in standard SQL.
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