Postgresql Syntax error at or near " THEN "

Question

I'm trying to create a view in Postgresql , but when I run this code appears this error:

syntax error at or near " THEN "

CREATE OR REPLACE VIEW VW_MONITOR_DEVICE AS
    SELECT
        P.POSIZIONE_DEVICE_ID AS MONITOR_DEVICE_ID,
        P.VALID AS VALID,
         [...]
        IF (VALID == FALSE THEN 'Valid' ELSE P.REASON_FOR_INVALID) AS DESCRIPTION,
         [...]
    FROM public.TA_POSIZIONI_DEVICE P
    JOIN ...

TA_POSIZIONI_DEVICE

• VALID (Boolean not null)

Answer 1

You should use CASE

The SQL CASE expression is a generic conditional expression, similar to if/else statements in other programming languages

CASE WHEN condition THEN result
     [WHEN ...]
     [ELSE result]
END

So,

CREATE OR REPLACE VIEW VW_MONITOR_DEVICE AS
    SELECT
        P.POSIZIONE_DEVICE_ID AS MONITOR_DEVICE_ID,
        P.VALID AS VALID,
         [...]
           CASE WHEN VALID = false THEN 'Valid'
                ELSE P.REASON_FOR_INVALID
           END AS DESCRIPTION,

         [...]
    FROM public.TA_POSIZIONI_DEVICE P
    JOIN ...