reuse of subqueries with different WHERE clause - sql

Question

I have a query which I looks schematically like this
WITH sub_base AS (
SELECT type,
CASE WHEN a < 10 THEN 'GOOD'
WHEN a BETWEEN 10 AND 100 THEN 'OK'
ELSE 'BAD'
END AS a_q,
...
CASE WHEN z < 5 THEN 'GOOD'
WHEN z BETWEEN 5 AND 50 THEN 'OK'
ELSE 'BAD'
END AS z_q
FROM tbl
),
SELECT sub_one AS (
SELECT 'one' AS type,
COUNT(CASE WHEN a_q = 'GOOD' THEN 1) a_good,
COUNT(CASE WHEN a_q = 'OK' THEN 1) a_ok,
COUNT(CASE WHEN a_q = 'BAD' THEN 1) a_bad,
...
COUNT(CASE WHEN z_q = 'GOOD' THEN 1) z_good,
COUNT(CASE WHEN z_q = 'OK' THEN 1) z_ok,
COUNT(CASE WHEN z_q = 'BAD' THEN 1) z_bad,
FROM sub_base
WHERE type = 'one'
),
SELECT sub_two AS (
SELECT 'two' AS type,
COUNT(CASE WHEN a_q = 'GOOD' THEN 1) a_good,
COUNT(CASE WHEN a_q = 'OK' THEN 1) a_ok,
COUNT(CASE WHEN a_q = 'BAD' THEN 1) a_bad,
...
COUNT(CASE WHEN z_q = 'GOOD' THEN 1) z_good,
COUNT(CASE WHEN z_q = 'OK' THEN 1) z_ok,
COUNT(CASE WHEN z_q = 'BAD' THEN 1) z_bad,
FROM sub_base
WHERE type = 'two'
),
SELECT sub_all AS (
SELECT 'all' AS type,
COUNT(CASE WHEN a_q = 'GOOD' THEN 1) a_good,
COUNT(CASE WHEN a_q = 'OK' THEN 1) a_ok,
COUNT(CASE WHEN a_q = 'BAD' THEN 1) a_bad,
...
COUNT(CASE WHEN z_q = 'GOOD' THEN 1) z_good,
COUNT(CASE WHEN z_q = 'OK' THEN 1) z_ok,
COUNT(CASE WHEN z_q = 'BAD' THEN 1) z_bad,
FROM sub_base
)
SELECT * FROM sub_one
UNION
SELECT * FROM sub_two
UNION
SELECT * FROM sub_all
I want to reuse the subqueries in sub_one, sub_two, sub_all because they are almost identical with the exception of type in SELECT and the WHERE condition.
How can I avoid copy-pasting these subqueries?

Answer 1

Use GROUP BY:
SELECT type,
COUNT(CASE WHEN a_q = 'GOOD' THEN 1) as a_good,
COUNT(CASE WHEN a_q = 'OK' THEN 1) as a_ok,
COUNT(CASE WHEN a_q = 'BAD' THEN 1) as a_bad,
...
COUNT(CASE WHEN z_q = 'GOOD' THEN 1) as z_good,
COUNT(CASE WHEN z_q = 'OK' THEN 1) as z_ok,
COUNT(CASE WHEN z_q = 'BAD' THEN 1) as z_bad,
FROM sub_base
WHERE type IN ('one', 'two', 'three') -- may not be needed
GROUP BY type;
In Postgres, I would further simplify this. You could use FILTER or summing binary values:
SELECT type,
SUM( (a_q = 'GOOD')::int ) as a_good,
SUM( (a_q = 'OK')::int ) as a_ok,
SUM( (a_q = 'BAD')::int ) as a_bad,
...
SUM( (z_q = 'GOOD')::int ) as z_good,
SUM( (z_q = 'OK')::int ) as z_ok,
SUM( (z_q = 'BAD')::int ) as z_bad,
FROM sub_base
WHERE type IN ('one', 'two', 'three') -- may not be needed
GROUP BY type;
I would also dispense with the CTE and just put the logic in the outer query directly, but that is more a matter of style.
EDIT:
You can use another CTE:
WITH . . . ,
t as (
SELECT type,
SUM( (a_q = 'GOOD')::int ) as a_good,
SUM( (a_q = 'OK')::int ) as a_ok,
SUM( (a_q = 'BAD')::int ) as a_bad,
...
SUM( (z_q = 'GOOD')::int ) as z_good,
SUM( (z_q = 'OK')::int ) as z_ok,
SUM( (z_q = 'BAD')::int ) as z_bad,
FROM sub_base
WHERE type IN ('one', 'two', 'three') -- may not be needed
GROUP BY type
)
SELECT t.*
FROM t
UNION ALL
SELECT 'Total', SUM(a_good), SUM(a_ok), SUM(a_bad), . . .
FROM t;

Answer 2

Why not using a second CTE?
WITH sub_base AS (
...
),
second_cte AS (
SELECT
type,
COUNT(CASE WHEN a_q = 'GOOD' THEN 1) a_good,
COUNT(CASE WHEN a_q = 'OK' THEN 1) a_ok,
COUNT(CASE WHEN a_q = 'BAD' THEN 1) a_bad,
...
COUNT(CASE WHEN z_q = 'GOOD' THEN 1) z_good,
COUNT(CASE WHEN z_q = 'OK' THEN 1) z_ok,
COUNT(CASE WHEN z_q = 'BAD' THEN 1) z_bad
FROM sub_base
)
SELECT
*
FROM second_cte
WHERE type = 'one'
UNION
SELECT
*
FROM second_cte
WHERE type = 'two'
UNION
SELECT
*
FROM second_cte
WHERE type = 'all'
You don't even need two CTE's in your case, because you don't reuse the first one. So you can put it into a subquery:
WITH cte AS (
SELECT
type,
COUNT(CASE WHEN a_q = 'GOOD' THEN 1) a_good,
COUNT(CASE WHEN a_q = 'OK' THEN 1) a_ok,
COUNT(CASE WHEN a_q = 'BAD' THEN 1) a_bad,
...
COUNT(CASE WHEN z_q = 'GOOD' THEN 1) z_good,
COUNT(CASE WHEN z_q = 'OK' THEN 1) z_ok,
COUNT(CASE WHEN z_q = 'BAD' THEN 1) z_bad
FROM (
SELECT
<your sub_base query here>
) s
)
SELECT
*
FROM second_cte
WHERE type = 'one'
UNION
SELECT
*
FROM second_cte
WHERE type = 'two'
UNION
SELECT
*
FROM second_cte
WHERE type = 'all'