How to use if in postgres?

Question

PostgreSQL

SELECT "F_TagName_ID",
          "F_Date",
          "F_ConvertedValue",
          IF (8 < to_char("F_Date", 'H24')::int
   AND to_char("F_Date", 'H24')::int < 20) THEN RETURN  2 AS smena ; ELSE  RETURN  1 AS smena;
   END IF;
   FROM "SC_Tag"."T_TagData"

how to use if-else

Answer 1

Use CASE
Something like this:

SELECT "F_TagName_ID",
          "F_Date",
          "F_ConvertedValue",
          CASE WHEN (8 < to_char("F_Date", 'H24')::int
   AND to_char("F_Date", 'H24')::int < 20) THEN  2  ELSE 1 END AS smena
   FROM "SC_Tag"."T_TagData"