IF-THEN-ELSE statements in postgresql

Question

I\'m looking to write a postgresql query to do the following :

if(field1 > 0,  field2 / field1 , 0)

I\'ve tried this query, but it\'s no

Answer 1

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)

Answer 2

case when field1>0 then field2/field1 else 0 end as field3

Answer 3

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>0 THEN field2/field1
    ELSE 0
  END 
  AS field3
FROM test