SELECT
    concat(
        'alter table ',
        table_schema,
        '.',
        table_name,
        ' modify column ',
        column_name,
        ' ',
        column_type,
        ' ',
    IF
        ( is_nullable = 'YES', IF ( data_type IN ( 'timestamp' ), ' null ', ' ' ), 'not null ' ),
    IF
        (
            column_default IS NULL,
            '',
        IF
            (
                data_type IN ( 'char', 'varchar' ) 
                OR data_type IN ( 'date', 'datetime' ) 
                AND column_default != 'CURRENT_TIMESTAMP',
                concat( ' default ''', column_default, '''' ),
                concat( ' default ', IF ( column_default = '', '''''', column_default ) ) 
            ) 
        ),
    IF
        ( extra IS NULL OR extra = '', '', concat( ' ', extra ) ),
        ' comment ''',
        ''';' 
) s 
FROM
    information_schema.COLUMNS 
WHERE
    table_schema = '數(shù)據(jù)庫名稱';

SELECT
concat( 'alter table ', table_schema, '.', table_name, ' comment ''', ''';' ) s 
FROM
    information_schema.COLUMNS 
WHERE
    table_schema = '數(shù)據(jù)庫名稱' 
GROUP BY
    TABLE_NAME;