mysql开发常用的几条sql查询语句

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 ;