Learning PostgreSQL 11 - Third Edition

Conditional statements

PostgreSQL supports the IF and CASE statements, which allow for execution based on a certain condition. PostgreSQL supports the IF statement construct, as follows:

• IF ... THEN ... END IF
• IF ... THEN ... ELSE ... END IF
• IF ... THEN ... ELSIF ... THEN ... ELSE ... END IF

The CASE statement comes in two forms, as follows:

• CASE ... WHEN ... THEN ... ELSE ... END CASE
• CASE WHEN ... THEN ... ELSE ... END CASE

To understand the IF statement, let's suppose that we would like to convert the advertisement rank in to text, as follows:

CREATE OR REPLACE FUNCTION cast_rank_to_text (rank int) RETURNS TEXT AS $$DECLARE  rank ALIAS FOR $1;  rank_result TEXT;BEGIN  IF rank = 5 THEN rank_result = 'Excellent'; ELSIF rank = 4 THEN rank_result ...