[Solved] Which of the following SQL queries correctly groups rows by a column that may contain NULL values? — Ans: SELECT category, COUNT(*) FROM products GROUP BY category; | SQL

SQL - GROUP BY and HAVING

Which of the following SQL queries correctly groups rows by a column that may contain NULL values?

ASELECT category, COUNT(*) FROM products GROUP BY category;

BSELECT category, COUNT(*) FROM products GROUP BY category WHERE category IS NOT NULL;

CSELECT category, COUNT(*) FROM products WHERE category IS NOT NULL GROUP BY category;

DSELECT category, COUNT(*) FROM products GROUP BY category HAVING category IS NOT NULL;

Step-by-Step Solution

Solution:

Step 1: Check GROUP BY syntax with NULLs
SELECT category, COUNT(*) FROM products GROUP BY category; uses correct syntax: grouping by category including NULLs. GROUP BY works with NULL values without extra filters.
Step 2: Analyze other options
Options A and D misuse WHERE and HAVING clauses with GROUP BY. SELECT category, COUNT(*) FROM products WHERE category IS NOT NULL GROUP BY category; filters out NULLs before grouping, which is valid but excludes NULL groups.
Final Answer:
SELECT category, COUNT(*) FROM products GROUP BY category; -> Option A
Quick Check:
GROUP BY with NULLs needs no special filter [OK]

Quick Trick: GROUP BY works directly with NULLs, no WHERE needed [OK]

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Which of the following SQL queries correctly groups rows by a column that may contain NULL values?