SQL query case when without else or do nothing? - sql

Question

Supposed I have some sample data in table_name_a as below:
code val_a val_b remark date
------------------------------------------
1 00001 500 0.1 111 20191108
2 00001 1000 0.2 222 20191109
3 00002 200 0.1 111 20191110
4 00002 400 0.3 222 20191111
5 00001 200 0.2 333 20191112
6 00001 400 0.1 444 20191113
My expected output as below:
code 111_a 111_b 222_a 222_b 333_a ....
--------------------------------------------
1 00001 500 .. .. .. ..
And below SQL query will contain 0 value which covered the correct values, does it possible to query without Else or do nothing?
SELECT code, date,
CASE WHEN t.remark='111' THEN t.val_a ELSE 0 END 111_a,
CASE WHEN t.remark='111' THEN t.val_b ELSE 0 END 111_b,
CASE WHEN t.remark='222' THEN t.val_a ELSE 0 END 222_a,
CASE WHEN t.remark='222' THEN t.val_b ELSE 0 END 222_b,
CASE WHEN t.remark='333' THEN t.val_a ELSE 0 END 333_a,
CASE WHEN t.remark='333' THEN t.val_b ELSE 0 END 333_b,
CASE WHEN t.remark='444' THEN t.val_a ELSE 0 END 444_a,
CASE WHEN t.remark='444' THEN t.val_b ELSE 0 END 444_b,
FROM table_name_a t

Answer 1

You need to use MAX with pivoting logic here, though you are on the right track:
SELECT
code,
MAX(CASE WHEN remark = '111' THEN val_a END) 111_a,
MAX(CASE WHEN remark = '111' THEN val_b END) 111_b,
MAX(CASE WHEN remark = '222' THEN val_a END) 222_a,
MAX(CASE WHEN remark = '222' THEN val_b END) 222_b,
MAX(CASE WHEN remark = '333' THEN val_a END) 333_a,
MAX(CASE WHEN remark = '333' THEN val_b END) 333_b,
MAX(CASE WHEN remark = '444' THEN val_a END) 444_a,
MAX(CASE WHEN remark = '444' THEN val_b END) 444_b
FROM table_name_a
GROUP BY
code;
The logic here works because for each group of records belonging to a single code, we take the maximum value only under certain conditions, in this case for certain values of remark. Should the condition be false, then the CASE expressions would return NULL, which would then be ignored by MAX.