SQL query to return a grouped result as a single row

Question

If I have a jobs table like:

|id|created_at  |status    |
----------------------------
|1 |01-01-2015  |error     |
|2 |01-01-2015  |complete  |
|3 |01-01-2015           


        

Answer 1

An actual crosstab query would look like this:

SELECT * FROM crosstab(
   $$SELECT created_at, status, count(*) AS ct
     FROM   jobs 
     GROUP  BY 1, 2
     ORDER  BY 1, 2$$

  ,$$SELECT unnest('{error,complete,"on hold"}'::text[])$$)
AS ct (date date, errors int, completed int, on_hold int);

Should perform very well.

Basics:

• PostgreSQL Crosstab Query

The above does not yet include the total per date.
Postgres 9.5 introduces the ROLLUP clause, which is perfect for the case:

SELECT * FROM crosstab(
 $$SELECT created_at, COALESCE(status, 'total'), ct
   FROM  (
      SELECT created_at, status, count(*) AS ct
      FROM   jobs 
      GROUP  BY created_at, ROLLUP(status)
      ) sub
   ORDER  BY 1, 2$$

  ,$$SELECT unnest('{total,error,complete,"on hold"}'::text[])$$)
AS ct (date date, total int, errors int, completed int, on_hold int);

Up to Postgres 9.4, use this query instead:

WITH cte AS (
    SELECT created_at, status, count(*) AS ct
    FROM   jobs 
    GROUP  BY 1, 2
    )
TABLE  cte
UNION  ALL
SELECT created_at, 'total', sum(ct)
FROM   cte 
GROUP  BY 1
ORDER  BY 1

Related:

• Grouping() equivalent in PostgreSQL?

---

If you want to stick to a simple query, this is a bit shorter:

SELECT created_at
     , count(*) AS total
     , count(status = 'error' OR NULL)    AS errors
     , count(status = 'complete' OR NULL) AS completed
     , count(status = 'on hold' OR NULL)  AS on_hold
FROM   jobs 
GROUP  BY 1;

count(status) for the total per date is error-prone, because it would not count rows with NULL values in status. Use count(*) instead, which is also shorter and a bit faster.

Here is a list of techniques:

• For absolute performance, is SUM faster or COUNT?

In Postgres 9.4+ use the new aggregate FILTER clause, like @a_horse mentioned:

SELECT created_at
     , count(*) AS total
     , count(*) FILTER (WHERE status = 'error')    AS errors
     , count(*) FILTER (WHERE status = 'complete') AS completed
     , count(*) FILTER (WHERE status = 'on hold')  AS on_hold
FROM   jobs 
GROUP  BY 1;

Details:

• How can I simplify this game statistics query?