常用mysql几条sql语句

SELECT DATE_FORMAT(FROM_DAYS(TO_DAYS(now()) - TO_DAYS(@dateofbirth)), '%Y') + 0;

UNIX_TIMESTAMP( dt2 ) - UNIX_TIMESTAMP( dt1 )

SELECT id FROM tbl GROUP BY id HAVING COUNT(*) = N;

SELECT COUNT(*) FROM calendar WHERE d BETWEEN Start AND Stop AND DAYOFWEEK(d) NOT IN(1,7) AND holiday=0; 　　

SELECT k.column_name FROM information_schema.table_constraints t
　　　　JOIN information_schema.key_column_usage k USING (constraint_name,table_schema,table_name)   

　　　　　　WHERE t.constraint_type='PRIMARY KEY' AND t.table_schema='db' AND t.table_name=tbl'

SELECT   

　　table_schema AS 'Db Name',
　　Round( Sum( data_length + index_length ) / 1024 / 1024, 3 ) AS 'Db Size (MB)',
　　Round( Sum( data_free ) / 1024 / 1024, 3 ) AS 'Free Space (MB)'
FROM information_schema.tables GROUP BY table_schema ;