The isnull problem in SQL.

Today when writing SQL code to write a ISNULL (variable 1, variable 2), the return of the result is actually "*", the asterisk, depressed for a long time.

The code has the following effect:

Declare @str1 varchar (1) Declare @str2 int Set @str2 = 222 Select ISNULL (@str1,@str2)

Return the result: "*", this depressed ah.

Modify the following code:

Declare @str1 varchar (4) Declare @str2 int Set @str2 = 222 Select ISNULL (@str1,@str2)

Returns the result: "222".

Modify the code again:

Declare @str1 varchar (4) Declare @str2 varchar (8) Set @str2 = ' 2222222 ' Select ISNULL (@str1,@str2)

Returns the result: "2222".

After these three test results: guessing the type of result returned by IsNull is closely related to the first variable, even depending on the type of the first variable.

Official explanation:

Syntax

(Check_,)

Arguments

Check_expression

Is the expression to being checked for NULL. check_expression can is of any type.

Replacement_value

is, the expression to being returned if check_expression is NULL. Replacement_value must be of a type, that's implicitly convertible to the type of check_expresssion.

Return Types

Returns the same type as check_expression.

Remarks

The value of check_expression is returned if it was not NULL; Otherwise, Replacement_value was returned after it was implicitly converted to the type of check_expression , if the types is different.

The return value is the second argument, which turns to the type of the first argument, the conversion fails, the exception is reported, or the preceding "*", the asterisk, appears.

The isnull problem in SQL.