Compare two MySQL DB Schemas

mysql_db_compare.sql

SET @source_db = 'db1';
SET @target_db = 'db2';

SELECT 
  'Only in source' exist_type,
  c1.table_schema, c1.table_name, c1.column_name, c1.ordinal_position, c1.column_default, c1.is_nullable, c1.numeric_precision, c1.numeric_scale, c1.character_set_name, c1.collation_name, c1.column_type, c1.column_key, c1.extra, c1.column_comment
FROM
  (SELECT * FROM information_schema.columns WHERE TABLE_SCHEMA = @source_db) c1
  LEFT JOIN (SELECT * FROM information_schema.columns WHERE TABLE_SCHEMA = @target_db) c2
    ON c1.TABLE_name = c2.TABLE_name AND c1.column_name = c2.column_name
WHERE c2.column_name is null

UNION ALL

SELECT
  'Only in target' exist_type,
  c2.table_schema, c2.table_name, c2.column_name, c2.ordinal_position, c2.column_default, c2.is_nullable, c2.numeric_precision, c2.numeric_scale, c2.character_set_name, c2.collation_name, c2.column_type, c2.column_key, c2.extra, c2.column_comment
FROM
  (SELECT * FROM information_schema.columns WHERE TABLE_SCHEMA = @source_db) c1
  RIGHT JOIN (SELECT * FROM information_schema.columns WHERE TABLE_SCHEMA = @target_db) c2
    ON c1.TABLE_name = c2.TABLE_name AND c1.column_name = c2.column_name
WHERE c1.column_name is null

UNION ALL

SELECT 
  'In both schemas' exist_type,
  CONCAT(c1.table_schema, '/', c2.table_schema),
  c1.table_name, c1.column_name,
  IF(c1.ordinal_position = c2.ordinal_position OR c1.ordinal_position IS NULL AND c2.ordinal_position IS NULL, NULL, CONCAT_WS('/', IFNULL(c1.ordinal_position, ''), IFNULL(c2.ordinal_position, ''))),
  IF(c1.column_default = c2.column_default OR c1.column_default IS NULL AND c2.column_default IS NULL, NULL, CONCAT_WS('/', IFNULL(c1.column_default, ''), IFNULL(c2.column_default, ''))),
  IF(c1.is_nullable = c2.is_nullable OR c1.is_nullable IS NULL AND c2.is_nullable IS NULL, NULL, CONCAT_WS('/', IFNULL(c1.is_nullable, ''), IFNULL(c2.is_nullable, ''))),
  IF(c1.numeric_precision = c2.numeric_precision OR c1.numeric_precision IS NULL AND c2.numeric_precision IS NULL, NULL, CONCAT_WS('/', IFNULL(c1.numeric_precision, ''), IFNULL(c2.numeric_precision, ''))),
  IF(c1.numeric_scale = c2.numeric_scale OR c1.numeric_scale IS NULL AND c2.numeric_scale IS NULL, NULL, CONCAT_WS('/', IFNULL(c1.numeric_scale, ''), IFNULL(c2.numeric_scale, ''))),
  IF(c1.character_set_name = c2.character_set_name OR c1.character_set_name IS NULL AND c2.character_set_name IS NULL, NULL, CONCAT_WS('/', IFNULL(c1.character_set_name, ''), IFNULL(c2.character_set_name, ''))),
  IF(c1.collation_name = c2.collation_name OR c1.collation_name IS NULL AND c2.collation_name IS NULL, NULL, CONCAT_WS('/', IFNULL(c1.collation_name, ''), IFNULL(c2.collation_name, ''))),
  IF(c1.column_type = c2.column_type OR c1.column_type IS NULL AND c2.column_type IS NULL, NULL, CONCAT_WS('/', IFNULL(c1.column_type, ''), IFNULL(c2.column_type, ''))),
  IF(c1.column_key = c2.column_key OR c1.column_key IS NULL AND c2.column_key IS NULL, NULL, CONCAT_WS('/', IFNULL(c1.column_key, ''), IFNULL(c2.column_key, ''))),
  IF(c1.extra = c2.extra OR c1.extra IS NULL AND c2.extra IS NULL, NULL, CONCAT_WS('/', IFNULL(c1.extra, ''), IFNULL(c2.extra, ''))),
  IF(c1.column_comment = c2.column_comment OR c1.column_comment IS NULL AND c2.column_comment IS NULL, NULL, CONCAT_WS('/', IFNULL(c1.column_comment, ''), IFNULL(c2.column_comment, '')))
FROM
  (SELECT * FROM information_schema.columns WHERE TABLE_SCHEMA = @source_db) c1
  JOIN (SELECT * FROM information_schema.columns WHERE TABLE_SCHEMA = @target_db) c2
    ON c1.TABLE_name = c2.TABLE_name AND c1.column_name = c2.column_name;

Compares DB1 against DB2