How to Avoid Naming Conflicts in SQL's GROUP BY and ORDER BY Clauses?

Column names in SQL GROUP BY and ORDER BY clauses

Question:

When grouping data in SQL, you must specify the correct column names in the GROUP BY and ORDER BY clauses. If there is a naming conflict between the input and output columns, the results may be incorrect.

Solution:

GROUP BY Clause

• Avoid using source column names: Do not use source column names (e.g. attempt.result) directly for grouping. Grouping should be done using a CASE expression that determines the desired result. This ensures you are grouping by the correct values.

    GROUP BY model.name, attempt.type, CASE WHEN attempt.result = 0 THEN 0 ELSE 1 END

• Use column aliases: If you prefer to use the original column names, provide a different alias in the SELECT list. This prevents the output columns from interfering with the grouping.

    SELECT ... , CASE WHEN attempt.result = 0 THEN 0 ELSE 1 END AS result1
    GROUP BY model.name, attempt.type, result1

ORDER BY Clause

• Use positional references: Instead of quoting the output column names directly, use positional references (ordinal numbers) in the ORDER BY clause. This avoids any potential naming conflicts.

    ORDER BY 1, 2, 3

Example:

Rewrite the query using correct JOIN syntax, positional references and resolving naming conflicts:

SELECT m.name,
       a.type,
       CASE WHEN a.result = 0 THEN 0 ELSE 1 END AS result,
       CURRENT_DATE - 1 AS day,
       count(*) AS ct
FROM   attempt a
JOIN   prod_hw_id p USING (hard_id)
JOIN   model m USING (model_id)
WHERE  ts >= '2013-11-06 00:00:00'
AND    ts <  '2013-11-07 00:00:00'
GROUP  BY 1, 2, 3
ORDER  BY 1, 2, 3;

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