对于上面这种情况,我们一般会先SELECT查出这条记录,然后根据查出记录的end_at再UPDATE start_at和end_at,伪代码如下(为uid是1001的会员续1个月): 复制代码代码如下: vipMember = SELECT * FROM vip_member WHERE uid=1001 LIMIT 1 # 查uid为1001的会员 if vipMember.end_at < NOW(): UPDATE vip_member S...
vipMember = SELECT * FROM vip_member WHERE uid=1001 LIMIT 1 FOR UPDATE # 查uid为1001的会员 if vipMember.end_at < NOW(): UPDATE vip_member SET start_at=NOW(), end_at=DATE_ADD(NOW(), INTERVAL 1 MONTH), active_status=1, updated_at=NOW() WHERE uid=1001 else: UPDATE vip_member ...
-- SELECT * FROM test.tb_student WHERE 1=1 and id='2' LIMIT 1 FOR UPDATE; -- 可以获取到 id = '2' 的锁-- 不论 会话窗口1 先开启的事务无论是否有 commit 或 rollback ,查询 id !='1' 的行数据时,因没有被加行锁,会立即返回数据SELECT*FROMtest.tb_studentWHERE1=1andid='1'LIMIT1...
我们可以使用 FOR UPDATE SKIP LOCKED 查询并锁定待处理的任务。此查询会锁定一行记录,如果该记录已被其他事务锁定,则跳过该记录,返回未被锁定的记录。 查询并锁定任务 START TRANSACTION; SELECT id, name FROM tasks WHERE status = 1 FOR UPDATE SKIP LOCKED LIMIT 1; 这个查询将: 锁定一个 status = 1(待处...
1. 可以优化为: select * from user where login_name=? limit 1 1. 自己明确知道只有一条结果,但数据库并不知道,明确告诉它,让它主动停止游标移动 17.SQL性能优化explain中的type:至少要达到 range 级别,要求是 ref 级别,如果可以是 consts 最好 ...
(1), (1); update t1 set a=3 where a = 1 limit 1; delete from t1 where a = 3 limit 1; --let $MYSQLD_DATADIR= `SELECT @@datadir` --exec $MYSQL_BINLOG -F -v $MYSQLD_DATADIR/master-bin.000001 === end test case === The output from mysqlbinlog for the update and dele...
SELECT rname FROM jbs WHERE stat = 'todo' LIMIT 1 FOR UPDATE; if there is a good index on stat, then only one row (and the 'gap' before it) becomes X-locked. Best regards, Heikki Oracle Corp./Innobase Oy InnoDB - transactions, row level locking, and foreign keys for MySQL ...
1.select * from table limit 1 for update; 本意是只想锁住(max-1,max](max,sumpernum],减少锁间隙 但是忘记主键索引默认正向有序,这样其实是锁住了(-supernum,1](1,2] 正确的写法是:select * from table order by desc limit 1 for update; ...
```sql UPDATE users SET email = 'john@example.com' WHERE id > 1 LIMIT 5;```这将更新 `...