Using CASE as a join condition in Hive - sql

Question

I'm trying to run a query in Hive where I run a join based on a case statement. For some reason, I'm having problems on lines 7 and 8. I have not been able to resolve the error which is
line 7: Expected: AND, AS, BETWEEN, DIV, ILIKE, IN, IREGEXP, IS, LIKE, NOT, OR, REGEXP, RLIKE CAUSED BY: Exception: Syntax error
line 8: Encountered: AS Expected: AND, BETWEEN, DIV, ILIKE, IN, IREGEXP, IS, LIKE, NOT, OR, REGEXP, RLIKE CAUSED BY: Exception: Syntax error
select * from dra_record_set.mark_set inv
INNER JOIN innerdb.name_set roll_table
on inv.record_id = roll_table.ply_record_id AND
roll_table.date =
(CASE
WHEN inv.purchase_day>0 AND inv.purhcase_date BETWEEN roll_table.discount_start_dt AND roll_table.discount_end_dt) THEN inv.purchase_date
ELSE WHEN (CONCAT(inv.purchase_yr,inv.purchase_mo,(CAST("15")AS INT))) AS temp_var BETWEEN roll_table.discount_start_dt AND roll_table.discount_end_dt) THEN inv.purchase_date
END AS temp_pur_dt)
WHERE inv.inroll_discount_eligible_flag =1
limit 10

Answer 1

case is an expression. It returns a value. Your seems to be more like a macro substitution for SQL code.
Remove the case and just use boolean logic:
from dra_record_set.mark_set inv join
innerdb.name_set roll_table
on inv.record_id = roll_table.ply_record_id and
( (inv.purchase_day > 0 and
inv.purhcase_date between roll_table.discount_start_dt and roll_table.discount_end_dt
) or
(inv.purchase_day <= 0 and
CONCAT(inv.purchase_yr, inv.purchase_mo, 15) between roll_table.discount_start_dt AND roll_table.discount_end_dt
)
)