Question

I want to rename columns in database programmatically and MySQL enforces me to specify column definition in CHANGE statement.

ALTER TABLE table_name CHANGE old_name new_name column_definition 

So, I want to build column definition from INFORMATION_SCHEMA.COLUMNS table. I’ve read answers which adjust me to parse output of SHOW CREATE TABLE table_name, but I do not want to do that in some reasons.

I want to get column definition as result of single SQL script if it is possible.

Answer 1

Try this:

select COLUMN_TYPE from INFORMATION_SCHEMA.COLUMNS WHERE TABLE_SCHEMA = '{database name}' AND TABLE_NAME = '{table name}' AND COLUMN_NAME = '{column name}';

You’ll need to fill in the right values, but it should give you the precise string you’ll need to fill into the ALTER statement. You will need to do some additional work to deal with default statements and NULL settings.

The complete sample:

SELECT CONCAT(
      CAST(COLUMN_NAME AS CHAR),
      ' ',
      CAST(COLUMN_TYPE AS CHAR),
      IF(ISNULL(CHARACTER_SET_NAME),
         '',
         CONCAT(' CHARACTER SET ', CHARACTER_SET_NAME)),
      IF(ISNULL(COLLATION_NAME), '', CONCAT(' COLLATE ', COLLATION_NAME)),
      ' ',
      IF(IS_NULLABLE = 'NO', 'NOT NULL ', ''),
      IF(IS_NULLABLE = 'NO' AND ISNULL(COLUMN_DEFAULT),
         '',
         CONCAT('DEFAULT ', QUOTE(COLUMN_DEFAULT), ' ')),
      UPPER(extra))
      AS column_definition
 FROM INFORMATION_SCHEMA.COLUMNS
WHERE  TABLE_SCHEMA = 'table_schema'
   AND TABLE_NAME = 'table_name'
   AND COLUMN_NAME = 'column_name';

EDIT Added quoting of default value, collation and charset.