Question

i have a details table with columns:

• user_id int
• code int
• value int

And i want to build a summary table that looks like:

• user_id int
• valueA int
• valueB int

In the details table, valueA would correspond to say, code 5, and valueB would correspond to say, code 6, so i’m looking for something like:

insert into summary (user_id,valueA,valueB) VALUES ( SELECT ??? from details );

The problem of course is that i’m looking at multiple rows from the “details” table to populate one row in the “summary” table.

Eg, if i had the following rows in details:

1  5  100
1  6  200
2  5  1000
2  6  2000

I want to end up with the following in the summary table:

1  100   200
2  1000  2000

Any ideas?

Answer 1

MySQL doesn’t have PIVOT/UNPIVOT syntax, which leaves you to use a combination of GROUP BY and CASE expressions:

INSERT INTO SUMMARY
  (user_id,valueA,valueB) 
  SELECT d.user_id,
         MAX(CASE WHEN d.code = 5 THEN d.value ELSE NULL END),
         MAX(CASE WHEN d.code = 6 THEN d.value ELSE NULL END),
    FROM DETAILS d
GROUP BY d.user_id