MySQL: How to add a column if it doesn't already exist?

Question

I want to add a column to a table, but I don't want it to fail if it has already been added to the table. How can I achieve this?

# Add column fails if it already exists 
ALTER TABLE `TableName` ADD `ColumnName` int(1) NOT NULL default '0';

Answer 1

Use the following in a stored procedure:

IF EXISTS( SELECT NULL
            FROM INFORMATION_SCHEMA.COLUMNS
           WHERE table_name = 'tablename'
             AND table_schema = 'db_name'
             AND column_name != 'columnname')  THEN

  ALTER TABLE `TableName` ADD `ColumnName` int(1) NOT NULL default '0';

END IF;

Reference:

• The INFORMATION_SCHEMA COLUMNS Table

Answer 2

http://www.cryer.co.uk/brian/mysql/howto_add_column_unless_exists.htm