Sarthaks Test
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Anjali writes the following commands with respect to a table employee having fields, empno, name, department, commission.

Command1 : Select count(*) from employee;

Command2: Select count(commission) from employee;

She gets the output as 4 for the first command but gets an output 3 for the second command. Explain the output with justification.

1 Answer

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Best answer

This is because the column commission contains a NULL value and the aggregate functions do not take into account NULL values. Thus Command1 returns the total number of records in the table whereas Command2 returns the total number of non NULL values in the column commission.

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