SELECT *,CONCAT(
'ALTER TABLE ', tableName,
' MODIFY ', columnName, ' VARCHAR(', columnLength, ') CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci ',
' DEFAULT ', IFNULL(QUOTE(columnDefault), "''"),
' COMMENT ', IFNULL(QUOTE(columnComment), "''"), ';'
) FROM (
SELECT table_name AS tableName, column_name AS columnName, character_maximum_length AS columnLength, column_default AS columnDefault, column_comment AS columnComment
FROM information_schema.columns
WHERE table_schema = 'db_performance_plus'
AND data_type = 'varchar'
AND character_set_name = 'utf8'
)T;