Given the Friends table:

ID   | NAME      | AGE
-------------------------
01   | Frank     | 18
02   | Sharon    | NULL
03   | John      | 20
04   | Jennifer  | NULL

How many records will the following query delete:

DELETE FROM Friends WHERE AGE = NULL;

Explanation

It is not possible to test for NULL values with comparison operators, such as =, <, or <>.
IS NULL and IS NOT NULL operators are used instead.

logical-operators

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