How to change the timstamp type to string with the below condition . Please refer full description

[#1]

How to change the timstamp type to string with the condition of

my query has CASE condition like. " WHEN a1.Col1 = '1' THEN "b1.col2" Else "" END as Col3"

here Col1 is timestamp and Col3 is String, So when i run the query, got this error .. ""Argument type mismatch '""': The expressions after THEN should have the same type: "timestamp" is expected but "string" is found"". I expect to here, if the condition failed i need to store "" (empty) value. Please help on this. Thanks in advance.

[#2 · Accepted solution]

Here is the solution for that

WHEN a1.Col1 = '1' THEN "b1.col2" Else CAST ('' as timestamp) END as Col3 . It will work