Detailed explanation of sql isnull usage

ISNULL

Replace NULL with the specified replacement value.

Syntax

：ISNULL (check_expression, replacement_value)

Parameters

check_expression The expression that will be checked to see if it is NULL. If it is not NULL, this value is returned directly, which is the expression check_expression . If it is empty, this will directly return the content of replacement_value. check_expression can be of any type.

replacement_value The expression that will be returned when check_expression is NULL. replacement_value must be of the same type as check_expresssion .

Return type

Returns the same type as check_expression.

Notes

If check_expression is not NULL, then return the value of the expression; otherwise, return replacement_value.

Example

1 Sample data

The table tb_Student and its sample data are shown in the figure below.

2. Query requirements

Query the student information whose score is less than or equal to 60 and save it to the table variable @tempTable , when the student's score is empty, the score is recorded as 0.

declare @tempTable table(
    stuname nchar(10),
    stuage int,
     stuscore float);
insert into @tempTable
select name,age,ISNULL(score,0) from tb_Student
where  ISNULL(score,0)<=60
select * from @tempTable

3 Execution results

Recommended tutorial: "sql tutorial"

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