IF-THEN-ELSE statements in postgresql

Question

I m looking to write a postgresql query to do the following    if field1  gt  0   field2   field1   0    I ve tried this query  but it s not working  if  field1  gt  0  then return field2   field1 as field3 else return 0 as field3   thank youu

User · Answer

case when field1 gt 0 then field2 field1 else 0 end as field3

User · Answer

As stated in PostgreSQL docs here      The SQL CASE expression is a generic conditional expression  similar to if else statements in other programming languages    Code snippet specifically answering your question   SELECT field1  field2    CASE     WHEN field1 gt 0 THEN field2 field1     ELSE 0   END    AS field3 FROM test

User · Answer

In general  an alternative to case when     is coalesce nullif x bad value  y   that cannot be used in OP s case   For example   select coalesce nullif y     x   coalesce nullif x     y     from        select  abc  as x     as y   union all  select  def  as x   ghi  as y   union all  select    as x   jkl  as y   union all  select null as x   mno  as y   union all  select  pqr  as x  null as y    q   gives    coalesce   coalesce    x     y   ---------- ---------- ----- -----  abc        abc        abc     ghi        def        def   ghi  jkl        jkl              jkl  mno        mno              mno  pqr        pqr        pqr     5 rows

[sql] IF-THEN-ELSE statements in postgresql

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