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Simple IF evaluation mistake in SQL Azure statement

Posted on 2016-09-27
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Last Modified: 2016-09-27
I'm doing something stupid and not evaluating a stored procedure parameter properly in an IF block.    (SQL Azure DB)

Here is the SP ....

ALTER PROCEDURE [dbo].[sp_ControlVariableCC]
      @Enable bit = NULL
AS
BEGIN
        DECLARE @Enable_Msg varchar(max) = 'error message text';

        IF (@Enable <> 0 AND @Enable <> 1) OR @Enable IS NULL
      BEGIN
            THROW 90002, @Enable_Msg, 1
      END;

This is just fluff SQL to ensure that the user doesn't enter something other than what they're supposed to and to provide a more detailed error message to the user than the system would generate.    If I don't enter in the parameter when calling the SP, it throws properly.   However, if I enter 2 for the parameter, it does not throw as expected.   I know I'm doing something extremely stupid here w/ the comparison logic.   Any help is very much appreciated!
0
Comment
Question by:trs28
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10 Comments
 
LVL 27

Accepted Solution

by:
Shaun Kline earned 1000 total points
ID: 41818269
It may not be an issue with the comparison logic. A bit variable can only have a value of 0, 1, or NULL. Your calling code may be treating the 2 as one of those values...most likely 1.
0
 
LVL 30

Expert Comment

by:Pawan Kumar
ID: 41818272
Try this..This will work.

ALTER PROCEDURE [dbo].[sp_ControlVariableCC]
      @Enable bit = NULL
AS 
BEGIN
        DECLARE @Enable_Msg VARCHAR(100) = 'error message text'

        IF (@Enable <> 0 AND @Enable <> 1) OR @Enable IS NULL      
            THROW 90002, @Enable_Msg, 1
      
END

Open in new window

0
 
LVL 22

Expert Comment

by:Kelvin Sparks
ID: 41818274
@Enable is a bit datatype. Valid options are 0 and 1. What tends to happen when passing integers is that 0 is treated as 0 and any other value becomes 1 (or true). The more correct way to evaluate but datatypes would be ID @Enable or NOT @Enable (i.e. IF (NOT @Enable AND @Enable )  but I suspect the same occurs.

I think that sort of checking needs to happen prior to passing the value to the SP.


Kelvin
0
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LVL 30

Expert Comment

by:Pawan Kumar
ID: 41818281
may be

ALTER PROCEDURE [dbo].[sp_ControlVariableCC]
      @Enable bit = NULL
AS 
BEGIN
        DECLARE @Enable_Msg VARCHAR(100) = 'error message text'

            IF @Enable IS NULL      
            THROW 90002, @Enable_Msg, 1
		ELSE IF @Enable != 1
			THROW 90002, @Enable_Msg, 1
		ELSE IF @Enable != 0
			THROW 90002, @Enable_Msg, 1
END

Open in new window

0
 
LVL 30

Expert Comment

by:Pawan Kumar
ID: 41818283
got it AND is the issue. try this

ALTER PROCEDURE [dbo].[sp_ControlVariableCC]
      @Enable bit = NULL
AS 
BEGIN
        DECLARE @Enable_Msg VARCHAR(100) = 'error message text'

        IF @Enable <> 0 OR @Enable <> 1 OR @Enable IS NULL      
            THROW 90002, @Enable_Msg, 1
      
END

Open in new window

0
 
LVL 30

Expert Comment

by:Pawan Kumar
ID: 41818299
tested one...

ALTER PROCEDURE [dbo].[sp_ControlVariableCC]
      @Enable bit = NULL
AS 
BEGIN
        DECLARE @Enable_Msg VARCHAR(100) = 'error message text'

            IF @Enable IS NULL      
            THROW 90002, @Enable_Msg, 1
		ELSE IF @Enable != 1
			THROW 90002, @Enable_Msg, 1
		ELSE IF @Enable != 0
			THROW 90002, @Enable_Msg, 1
END

Open in new window

0
 
LVL 30

Expert Comment

by:Pawan Kumar
ID: 41818308
Pls wait.
0
 
LVL 30

Assisted Solution

by:Pawan Kumar
Pawan Kumar earned 1000 total points
ID: 41818357
Okay I got why it is not working.

The problem in when you are passing 2 or any number greater than 1 Bit field will contain 1 only. That's why that error is not coming..

Script to test the above case

CREATE TABLE Bits
(
	ID BIT
)
GO

INSERT INTO Bits VALUES (100)

INSERT INTO Bits VALUES (0)

INSERT INTO Bits VALUES (1)

SELECT * FROM Bits

Open in new window


Now change the bit field to tinyint, updated code for you !!

ALTER PROCEDURE [dbo].[sp_ControlVariableCC]
      @Enable TINYINT = NULL
AS 
BEGIN
        DECLARE @Enable_Msg VARCHAR(100) = 'error message text'

        IF @Enable <> 0 OR @Enable <> 1 OR @Enable IS NULL      
            THROW 90002, @Enable_Msg, 1
      
END

Open in new window


Enjoy !! Good learning..
0
 

Author Comment

by:trs28
ID: 41818464
Thanks everyone for the assistance!   I knew I was doing something stupid and staring me right in the face the whole time!
0
 

Author Closing Comment

by:trs28
ID: 41818467
Pawan Kumar Khowal put in a little bit of time and effort into working this out.  Even though Shaun Kline was first and completely accurate, I had to reward the effort even after it was already figured out.
0

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