Create rule to restrict special characters in table in sql server

Question

I want to create a rule to restrict special characters to be entered into a column. I have tried the following. But it didnt work.

CREATE RULE rule_spchar
AS
@ma         


        

Answer 1

It's important to remember Microsoft's plans for the features you're using or intending to use. CREATE RULE is a deprecated feature that won't be around for long. Consider using CHECK CONSTRAINT instead.

Also, since the character exclusion class doesn't actually operate like a RegEx, trying to exclude brackets [] is impossible this way without multiple calls to LIKE. So collating to an accent-insensitive collation and using an alphanumeric inclusive filter will be more successful. More work required for non-latin alphabets.

M.Ali's NOT LIKE '%[^A-Z0-9 ]%' Should serve well.

Answer 2

Your can create a Check Constraint on this column and only allow Numbersand Alphabets to be inserted in this column, see below:

Check Constraint to only Allow Numbers & Alphabets

ALTER TABLE Table_Name 
ADD CONSTRAINT ck_No_Special_Characters 
       CHECK (Column_Name NOT LIKE '%[^A-Z0-9]%') 

Check Constraint to only Allow Numbers

ALTER TABLE Table_Name 
ADD CONSTRAINT ck_Only_Numbers 
       CHECK (Column_Name NOT LIKE '%[^0-9]%') 

Check Constraint to only Allow Alphabets

ALTER TABLE Table_Name 
ADD CONSTRAINT ck_Only_Alphabets 
       CHECK (Column_Name NOT LIKE '%[^A-Z]%') 

Answer 3

M.Ali's answer represents the best practice for the solution you describe. That being said, I read your question differently(i.e What is wrong with they way you're implementing the like comparison.)

1. You are not properly escaping wildcard characters.
2. The expression 'AB' LIKE '%[AB]% is true. The expression 'ZB' LIKE '%[^AB]%' is also true, since that statement is the equivalent of 'Z' LIKE '[^AB]' OR 'A' LIKE '[^AB]' Instead, you should use 'YZ' NOT LIKE '%[^AB]%' which is the equivalent of 'Y' NOT LIKE '%[^AB]%' AND 'Z' NOT LIKE '%[^AB]%'
3. You didn't escape the single quote or invisible characters. Take a look at the the ASCII characters. You would be better served implementing a solution like M.Ali's and adding any characters you do not wish to exclude.

The following script demonstrates the formation of a complex wildcard statement that consists of special characters.

-- Create sample data
-- Experiment testing various characters
DECLARE @temp TABLE (id INT NOT NULL, string1 varchar(10) NOT NULL)

INSERT INTO @temp
        (id,string1)
SELECT 1, '12]34'
UNION 
SELECT 2, '12[34'
UNION 
SELECT 3, '12_34'
UNION 
SELECT 4, '12%34'
UNION 
SELECT 5, '12]34'

SET NOCOUNT ON
DECLARE @SQL_Wildcard_Characters VARCHAR(512),
@Count_SQL_Wildcard_Characters INT,
@Other_Special_Characters VARCHAR(255),
@Character_Position INT,
@Escape_Character CHAR(1),
@Complete_Wildcard_Expression VARCHAR(1024)
SET @Character_Position = 1

-- Note these need to be escaped: 
SET @SQL_Wildcard_Characters = '[]^%_'
-- Choose an escape character.  
SET @Escape_Character = '~'
-- I added the single quote (') ASCII 39 and the space ( ) ASCII 32.  
-- You could also add the actual characters, but this approach may make it easier to read.
SET @Other_Special_Characters = '*|\":<>{}`\();@&$' + CHAR(39) + CHAR(32)

-- Quick loop to escape the @SQL_Wildcard_Characters
SET @Count_SQL_Wildcard_Characters = LEN(@SQL_Wildcard_Characters)
WHILE @Character_Position < 2*@Count_SQL_Wildcard_Characters
BEGIN
    SET @SQL_Wildcard_Characters = STUFF(@SQL_Wildcard_Characters,@Character_Position,0,@Escape_Character)
    SET @Character_Position = @Character_Position + 2
END
-- Concatenate the respective strings
SET @Complete_Wildcard_Expression = @SQL_Wildcard_Characters+@Other_Special_Characters

-- Shows how the statment works for match
SELECT ID, string1, @Complete_Wildcard_Expression AS [expression]
FROM @temp
WHERE string1 LIKE '%['+@Complete_Wildcard_Expression+']%' ESCAPE @Escape_Character

-- Show how the statement works fo non-match
SELECT ID, string1, @Complete_Wildcard_Expression AS [expression]
FROM @temp
WHERE string1 NOT LIKE '%[^'+@Complete_Wildcard_Expression+']%' ESCAPE @Escape_Character