SQL for update

1 select * from TTable1 for update 锁定表的所有行，只能读不能写 

2 select * from TTable1 where pkid = 1 for update 只锁定pkid=1的行 

3 select * from Table1 a join Table2 b on a.pkid=b.pkid for update 锁定两个表的所有记录 

4 select * from Table1 a join Table2 b on a.pkid=b.pkid where a.pkid = 10 for update 锁定两个表的中满足条件的行 

5. select * from Table1 a join Table2 b on a.pkid=b.pkid where a.pkid = 10 for update of a.pkid 只锁定Table1中满足条件的行