CODEWITHSUNDEEP
sqlpostgresqlgroup-bystring-comparison
user3557405
user3557405

Reputation: 626

consolidate column values only if same

I have a table with the following structure:

category | col_a | col_b
---------+-------+------
cat_1    |   1.0 | X
cat_1    |   0.0 | X
cat_1    |   1.0 | Y
cat_2    |   2.0 | Z
cat_2    |   1.0 | Z

Values in col_a (float values) need to be simply summed - no issues here. However, I want to consolidate all col_b (strings) values only if all values are the same per category, otherwise return null. So final output should be like below:

category | sum_a | same_or_none_b
---------+-------+---------------
cat_1    |   2.0 | null
cat_2    |   3.0 | Z

Can someone kindly help or direct me towards a solution? Thank you.

Upvotes: 0

Views: 33

Answers (1)

Laurenz Albe
Laurenz Albe

Reputation: 246523

You could use a CASE expression to distinguish the two cases:

SELECT category,
       sum(col_a) AS sum_a,
       CASE WHEN count(DISTINCT col_b) = 1
            THEN min(col_b)
       END AS same_or_none_b
FROM tab
GROUP BY category;

Upvotes: 3

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