求一个sql 语句

Question

mysql> select * from tasks;
+--------+--------+------+--------+
| taskid | comnum | sum  | status |
+--------+--------+------+--------+
| aaaa   |      1 |   30 |      0 |
| aaaa   |      1 |   30 |      0 |
| aaaa   |      1 |   30 |      0 |
| aaaa   |      1 |   30 |      0 |
| AARP   |      9 |   30 |      0 |
+--------+--------+------+--------+mysql> select * from user_task
    -> ;
+------------------------+--------+
| userid                 | taskid |
+------------------------+--------+
| aaaa                   | AARP   |
| aaaa                   | AARP   |
| aaaa                   | AARP   |
| aaaa                   | AARP   |
| aaaa                   | AARP   |
| aaaa                   | AARP   |
| LKjtPf8JE43U46ctqMLa1A | aaaa   |
+------------------------+--------+user_task 表为userid 已完成的tasked 列表，
我想从tasks 里，把userid ＝ LKjtPf8JE43U46ctqMLa1A 没有完成的纪录选出来，也就是 | AARP   |      9 |   30 |      0 |sql 语句改怎么写啊

Answer 1

效率不高、记得简历索引select * from tasks where taskid not  in(select taskid from user_task where userid = 'LKjtPf8JE43U46ctqMLa1A ');

Answer 2

select * from tasks where not exists (select 1 from user_task where taskid=tasks.taskid and userid = 'LKjtPf8JE43U46ctqMLa1A')