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There are two ways to assign values to defined variables in SQL Server, which are SET and SELECT.

The following is a comparison of the differences between the two assignment methods:

Setselect simultaneously assigns values to multiple variables does not support expression returning multiple values error assigns the last value returned to the variable expression does not return value variable is assigned null value variable keeps the original value

SQL Server recommends using SET instead of SELECT to assign values to variables.

The SET method is recommended when an expression returns a value and assigns a variable.

Note: SELECT can also assign the value of a scalar quantum query to a variable, and if the scalar quantum query does not return a value, the variable is set to a null value. This is exactly the same as using SET assignment

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