Unexpected result of case expression

Question

The following case expression results in a,

select case 0 when true  then 'c' when 'true1222' then 'a' else 'b' end;  

Anyone knows why? How could 0 be equal to true1222?

Answer 1

the problem is - use 0 as CASE, 0 == false so query compare:

• TRUE - not, go forward
• 'true1222' - FALSE == 0, OK

try to change query:

SELECT
    CASE 3
WHEN TRUE THEN
    'c'
WHEN 'true1222' THEN
    'a'
ELSE
    'b'
END;

and it return expected - 'b'