Set a variable inside case statement in mysql - mysql

Question

I have the following scenario
SELECT
...
...
(
#var1 = MAX(IF(table1.name='Mod', table1.value, NULL))
#var2 = MAX(IF(table1.name='Man', table1.value, NULL))
CASE
WHEN #var1 IS NOT NULL && #var2 IS NOT NULL THEN #var1+"/"+#var2
WHEN #var1 IS NULL && #var2 IS NOT NULL THEN #var2
WHEN #var1 IS NOT NULL && #var2 IS NULL THEN #var1
ELSE NULL
END) AS "col44",
This is throwing me an exception in the mysql console.
Can't we do a variable assignment in the general mysql select query?

Answer 1

What about this?
SELECT ...
, #var1 = MAX(IF(table1.name='Mod', table1.value, NULL))
, #var2 = MAX(IF(table1.name='Man', table1.value, NULL))
, CASE
WHEN #var1 IS NOT NULL && #var2 IS NOT NULL THEN #var1+"/"+#var2
WHEN #var1 IS NULL && #var2 IS NOT NULL THEN #var2
WHEN #var1 IS NOT NULL && #var2 IS NULL THEN #var1
ELSE NULL
END AS "col44"
Note the addition of commas, and removal of parenthesis.
Alternatively, you could just use a subquery. (In my experience, variables in queries can become unpredictable when used in conjunction with aggregation; this avoids the variables altogether).
SELECT ...
, CASE
WHEN modMax IS NOT NULL && manMax IS NOT NULL THEN modMax+"/"+manMax
WHEN modMax IS NULL && manMax IS NOT NULL THEN manMax
WHEN modMax IS NOT NULL && manMax IS NULL THEN modMax
ELSE NULL
END AS "col44"
FROM (
SELECT ...
, MAX(IF(table1.name='Mod', table1.value, NULL)) AS modMax
, MAX(IF(table1.name='Man', table1.value, NULL)) AS manMax
...
) AS subQ
Additional note: Watch out for modMax+"/"+manMax; it may end up giving you an integer calculated from modMax+0+manMax, instead of a string.