not+in+和+not+exists的区别
时间: 2023-11-16 17:04:38 浏览: 39
not in和not exists都是用于条件判断的关键字,但是它们的使用场景和含义略有不同。
not in用于判断某个值是否不在一个序列中,例如:
```
a = [1, 2, 3]
if 4 not in a:
print("4不在a中")
```
not exists用于判断一个子查询是否为空,例如:
```
SELECT *
FROM table1
WHERE NOT EXISTS (SELECT * FROM table2 WHERE table1.id = table2.id);
```
这个查询语句的意思是:从table1中选择所有行,其中id不在table2中出现过的行。
因此,not in和not exists的区别在于它们所作用的对象不同。not in作用于序列,而not exists作用于子查询。
相关问题
not+exists替代
以下是使用not exists替代not in的示例代码:
```sql
-- 插入实验数据
insert into TMP_B values (1, 'user1', 'info1');
insert into TMP_B values (2, 'user2', 'info2');
insert into TMP_B values (3, 'user3', 'info3');
-- 使用not exists替代not in
merge into B b
using TMP_B tb
on (tb.userid = b.userid)
when not matched then
insert (b.id, b.userid, b.info)
values (tb.id, tb.userid, tb.info)
where not exists (
select 1 from B where B.userid = tb.userid
);
```
The+chosen+package+location+already+exists+but+was+not+previously+created+using+this+Movelt!+Setup+A
The error message "The chosen package location already exists but was not previously created using this Movelt! Setup A" typically occurs when you are trying to install a package using the Movelt! Setup A tool, but the package location already exists and was not created using this tool.
To resolve this issue, you have a few options:
1. Delete the existing package location: You can manually delete the existing package location and then try installing the package again using Movelt! Setup A. Make sure to back up any important files or data in the package location before deleting it.
2. Choose a different package location: If you don't want to delete the existing package location, you can choose a different location for installing the package. During the installation process, specify a new directory or folder where you want the package to be installed.
3. Use a different installation method: If you are encountering difficulties with Movelt! Setup A, you can try using a different installation method or tool. Check if there are alternative installation options available for the package you are trying to install.