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

SQL - GROUP BY and HAVING

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

ASELECT col, COUNT(*) FROM table GROUP BY col WHERE col IS NOT NULL;

BSELECT col, COUNT(*) FROM table GROUP BY col;

CSELECT col, COUNT(*) FROM table WHERE col IS NOT NULL GROUP BY col;

DSELECT col, COUNT(*) FROM table GROUP BY col HAVING col IS NOT NULL;

Step-by-Step Solution

Solution:

Step 1: Review GROUP BY syntax with NULLs
GROUP BY can include NULL values; no special syntax needed to group NULLs.
Step 2: Check each option for correctness
SELECT col, COUNT(*) FROM table GROUP BY col; is correct syntax and groups NULLs as one group. Options B and D misuse WHERE/HAVING clauses. SELECT col, COUNT(*) FROM table WHERE col IS NOT NULL GROUP BY col; filters out NULLs before grouping.
Final Answer:
SELECT col, COUNT(*) FROM table GROUP BY col; -> Option B
Quick Check:
GROUP BY includes NULLs without extra filters [OK]

Quick Trick: GROUP BY works with NULLs without filters [OK]

Common Mistakes:

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