COUNT(*) vs. COUNT(column-name): When Should I Use Which?

Distinguishing Count(*) from Count(column-name): Making the Right Choice

In SQL, the count function is utilized to determine the number of rows in a table or a specific column. However, the choice between count(*) and count(column-name) can raise uncertainties.

Count(*):

Count(*) counts all rows within the specified range, regardless of whether or not they contain null values. It functions as a more comprehensive count, encompassing both non-null and null entries.

Count(column-name):

Count(column-name), on the other hand, counts only non-null values within the specified column. Null values are excluded from the count. This option provides a more precise count of actual data entries.

Implications for Usage:

The decision between count() and count(column-name) hinges on the intended outcome. If the count should include both null and non-null values, count() should be used. If null values should be excluded, count(column-name) is recommended.

Equivalent Functionalities:

Count(1) is identical in functionality to count(*) since 1 is always evaluated as non-null.

Choosing the Appropriate Function:

The choice between count() and count(column-name) depends on the specific requirements of the query. Count() provides a more comprehensive count, while count(column-name) filters out null values for a more accurate tally. The desired output should dictate which function to employ.

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