六条比较有用的MySQL数据库操作的SQL语句小结

复制代码 代码如下:

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

复制代码 代码如下:

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

复制代码 代码如下:

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'

复制代码 代码如下:

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 ;