MySQL: How to create Column if not exists?

Actually exists now for Maria DB 10.219

ALTER TABLE test ADD COLUMN IF NOT EXISTS column_a VARCHAR(255);

Bonus, it works for MODIFY as well

ALTER TABLE test MODIFY IF EXISTS column_a VARCHAR(255);

MySQL ALTER TABLE does not have IF EXISTS specification.

You can do the following through using a stored proc or a programming language if this is something that you'll need to do on a regular basis:

Pseudocode:

• Find if the column exists using the SQL below:

  SELECT column_name FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_SCHEMA=[Database Name] AND TABLE_NAME=[Table Name];

• If the above query returns a result then it means the column exists, otherwise you can go ahead and create the column.

You can use this solution, already mentioned on another StackOverFlow post: (Ref.: https://stackoverflow.com/a/31989541/)

MySQL - ALTER TABLE to add a column if it does not exist:

SET @dbname = DATABASE();
SET @tablename = "tableName";
SET @columnname = "colName";
SET @preparedStatement = (SELECT IF(
  (
    SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS
    WHERE
      (table_name = @tablename)
      AND (table_schema = @dbname)
      AND (column_name = @columnname)
  ) > 0,
  "SELECT 1",
  CONCAT("ALTER TABLE ", @tablename, " ADD ", @columnname, " INT(11);")
));
PREPARE alterIfNotExists FROM @preparedStatement;
EXECUTE alterIfNotExists;
DEALLOCATE PREPARE alterIfNotExists;