How do you strip a character out of a column in SQL Server?

The devil is in the details

The REPLACE function tends to be suitable for most scenarios. However, SQL has its intricacies, especially when handling NULL values or wildcard pattern characters.

NULL is not null

A NULL value in SQL signifies absence of data, and REPLACE does not affect NULL data. Therefore:

UPDATE TableName
SET ColumnName = REPLACE(ColumnName, '*', '')
WHERE ColumnName IS NOT NULL;


Wild, wild cards

To filter wildcard characters (%, _, [, ], and ^), escape with square brackets:

UPDATE TableName
SET ColumnName = REPLACE(ColumnName, '[%]', '');


Safely preview before you dive

Large data sets make efficiency vital. To gauge the impact, preview results with a SELECT statement:

SELECT REPLACE(ColumnName, '*', '') AS PreviewColumn
FROM TableName;


This offers a safety net, ensuring the desired effect before committing the changes.

The 'SELECT' in disguise

The SELECT statement, paired with REPLACE, facilitates temporary character removal for data analysts needing clean data for reports.

Announcing your presence

Generate clean data for analysis or reporting without original data modification:

SELECT REPLACE(ColumnName, '*', '') AS CleanColumn
FROM TableName;


A sneak peek into updates

Verify update effects by simulating their impact:

SELECT ColumnName, REPLACE(ColumnName, '*', '') AS SimulatedColumn
FROM TableName;


Keeping an UPDATE on your data integrity

While UPDATE operations are great, be careful not to unintentionally sabotage your data integrity. Test the changes thoroughly before going live.

A step-by-step tutorial...sort of

Turn your update routines transactional to review changes before finalizing them:

BEGIN TRANSACTION;
UPDATE TableName
SET ColumnName = REPLACE(ColumnName, '*', '');
-- It's like proofreading your thesis...then COMMENCE the party!
-- COMMIT;
-- SELECT 'Rollback, rollback, rollback!' FROM TableName WHERE PlansGoneWrong = 1;
-- ROLLBACK;


No, seriously. Back it up.

You've got precious data. So, back it up!

BACKUP DATABASE YourDatabaseName TO DISK = 'C:\Backups\YourDatabaseName.bak';


Larger-than-life datasets

Stripping characters from huge databases can be tasking. Let's keep it lean and mean.

Little drops of water...

Take it piece by piece. If your tables are large, implement the replacement in partitions:

WHILE (1 = 1)
BEGIN
    UPDATE TOP (1000) TableName
    SET ColumnName = REPLACE(ColumnName, '*', '')
    WHERE CHARINDEX('*', ColumnName) > 0;
    IF @@ROWCOUNT = 0 BREAK;
	-- BREAKing news: all asterisks expelled from Kingdom SQL!
END


Faster than a speeding query

Column lookups should be swift. Indexing can ensure speed, particularly for frequently accessed columns:

CREATE INDEX IX_TableName_ColumnName ON TableName(ColumnName);
-- Fast and Furious: SQL Drift
