delete from student where T_name = "张三"; 1. (5)delete 操作以后,使用optimize table table_name;会立刻释放磁盘空间,不管是 innodb 还是 myisam; 实例,删除学生表中姓名为 "张三" 的数据: delete from student where T_name = "张三"; optimize table student; 1. 2. delete from 表以后虽然未释放...
delete a from #T a where exists(select 1 from #T where Name=a.Name and ID<a.ID) 方法2: delete a from #T a left join (select min(ID)ID,Name from #T group by Name) b on a.Name=b.Name and a.ID=b.ID where b.Id is null 方法3: delete a from #T a where ID not in (...
FROM pg_class a LEFT OUTERJOIN pg_description bON b.objsubid=0AND a.oid = b.objoid WHERE a.relnamespace = (SELECT oidFROM pg_namespaceWHERE nspname='public')--用户表一般存储在public模式下 AND a.relkind='r' ORDERBY a.relname 使用表名查询表字段的定义 SELECT a.attnum, a.attnameAS...
postgres@[local:/tmp]:1999=#54672 delete from tab where id <= 800000;DELETE800000 postgres@[local:/tmp]:1999=#54672 SELECT pg_size_pretty(pg_relation_size('tab')) as table_size, pg_size_pretty(pg_relation_size('tab_pkey')) as index_size_pk, pg_size_pretty(pg_relation_size('idx...
A. not in、not exists 子查询可以改用 right join 代替 B. 查询嵌套层次越多,效率越高,因此应当多使用嵌套子查询 C. in、exists 子查询可以用 inner join 代替 D. 不要用含有 count(*) 的子查询判断是否存在记录,最好使用 left join 或 exists 查看完整题目与答案 下列SQL语句优化描述正...
run("DELETE FROM book WHERE title = :title", title="Phineas Finn") >>> con.run("ROLLBACK") >>> for row in con.run("SELECT * FROM book"): ... print(row) [1, "Ender's Game"] [2, 'The Magus'] [3, 'Phineas Finn'] >>> >>> con.close()...
One of nil, :delete, :destroy. Set nil when no deletion should occur. :delete to delete associated record in SQL, :destroy to call #destroy on the associated object. nil has_one Declares a has one relationship. This will add the following methods: association returns the associated object ...
update poi_hn_edit_0826 asetdel_flag=1,del_reason=3fromhn_normal_repair_fail bwherea.hn_id=b.hn_id;deletefromt1 ausingt2 bwherea.id=b.id;deletefromt1whereexists(selectidfromt2wheret1.id=t2.id); with with sub1as(selecthn_id,road_idfrompoi_hn_road),sub2as(selectdistinct hn_id...
49 -- delete row from table DELETE FROM warehouse where warehouse_id = 3; -- update a row of table UPDATE warehouse set warehouse_name = 'UPS_NEW' where warehouse_id = 1; -- explain a table EXPLAIN SELECT warehouse_id, warehouse_name FROM warehouse WHERE warehouse_name LIKE 'TV' ...
bool hasReturning; /* is it insert|update|delete RETURNING? */ bool hasModifyingCTE; /* has insert|update|delete in WITH? */ bool canSetTag; /* do I set the command result tag? */ bool transientPlan; /* redo plan when TransactionXmin changes? */ ...