Why do the execution result to NULL?-CodePudding

WireType won a record in the field of value, the result is null, what reason is this?

 
Declare @ sqlTemp varchar (1000) 
Declare @ wireType varchar (32) 
The set @ sqlTemp='select' + @ wireType + '=wireType from wire_t where wireCode=010' 
The exec (@ sqlTemp) 
Select @ wireType

CodePudding user response:

 
- so sweet 
Declare @ wireType varchar (32) 
Select @ wireType=wireType from wire_t where wireCode=010 
Select @ wireType

CodePudding user response:

Thank you for your reply, you this way no problem, I want to know where is the way I wrote wrong?

CodePudding user response:

Don't @ wireType assignment, the default is null, the select @ wireType, of course, is the result of the null luo

 
Declare @ sqlTemp varchar (1000) 
Declare @ wireType varchar (32) 
The set @ wireType='XXXXXX' 
The set @ sqlTemp='select' + @ wireType + '=wireType from wire_t where wireCode=010' 
The EXEC (@ sqlTemp) 
Select @ wireType

CodePudding user response:

 declare @ sqlTemp varchar (1000) 
Declare @ wireType varchar (32) 
The SET @ wireType='1' 
The set @ sqlTemp='select' + @ wireType + '=wireType from wire_t where wireCode=010' 
PRINT @ sqlTemp 
The exec (@ sqlTemp) 
Select @ wireType

You'll know it in the code printed, the fifth line to add a PRINT, right on the second floor, @ wireType variable assignment, SQL query results

CodePudding user response:

Declare @ sqlTemp varchar (1000)
The set @ sqlTemp='declare @ wireType varchar (32);
Select @ wireType=wireType from wire_t where wireCode=010;
Select '@ wireType="' + @ wireType '
The exec (@ sqlTemp)

CodePudding user response:

Exec (@ sqlTemp) in the parentheses variables can only be defined within the exec string, your mistake is not understand the problem of the exec variable scope