If a table has a column with some NULL values and you run SELECT col, COUNT(*) FROM table GROUP BY col;, how many groups will the NULL values form?

easy📝 Conceptual Q2 of 15

SQL - GROUP BY and HAVING

If a table has a column with some NULL values and you run SELECT col, COUNT(*) FROM table GROUP BY col;, how many groups will the NULL values form?

ANo group, NULLs are excluded

BOne group containing all NULL values

CMultiple groups, one for each NULL

DTwo groups, one for NULL and one for non-NULL

Step-by-Step Solution

Solution:

Step 1: Analyze GROUP BY with COUNT and NULL
COUNT(*) counts all rows, and GROUP BY treats all NULLs as one group.
Step 2: Determine number of groups for NULL
All NULL values in the column form a single group in the result.
Final Answer:
One group containing all NULL values -> Option B
Quick Check:
GROUP BY NULL forms one group [OK]

Quick Trick: COUNT(*) counts all rows including NULL groups [OK]

Common Mistakes:

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