oracle not in 和 not exist区别
时间: 2023-08-29 10:07:28 浏览: 57
Oracle中的NOT IN和NOT EXISTS都是用于查询语句中的条件筛选。它们之间的主要区别如下:
1. NOT IN需要一个完整的列表,而NOT EXISTS只需要一个子查询。
2. NOT IN比NOT EXISTS更适合用于处理简单的查询,而NOT EXISTS对于处理复杂的查询更加有效。
3. NOT IN在使用时应该小心,因为它可能会返回错误的结果,特别是在使用空值时。而NOT EXISTS不会受到空值的影响。
4. NOT EXISTS通常比NOT IN更快,因为它能够使用更优秀的查询优化技术。
总之,NOT EXISTS通常比NOT IN更加灵活和高效,但是在某些情况下,NOT IN也可以起到很好的作用。具体使用哪个取决于查询的复杂程度和实际需求。
相关问题
oracle not exist
在Oracle中,NOT EXISTS是一种用于查询的条件语句。它用于检查子查询的结果集是否为空,如果为空,则返回True,否则返回False。\[1\] NOT EXISTS的执行方式是,首先执行子查询,并将获取的结果存在一个有索引的临时表中。在执行子查询之前,主查询处于挂起状态,直到子查询执行完毕并将结果存放在临时表中后,主查询才会执行。\[2\] NOT EXISTS通常用于在查询中排除满足某个条件的记录。例如,如果要查询所有部门信息中平均工资不小于1500的部门,可以使用NOT EXISTS语句。\[3\]
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oracle schema does not exist
This error message indicates that the schema you are trying to access does not exist in the Oracle database.
You can check if the schema exists by querying the ALL_USERS view:
```
SELECT * FROM ALL_USERS WHERE USERNAME='<schema_name>';
```
If the schema does not exist, you will need to create it. To create a schema in Oracle, you can use the CREATE USER statement:
```
CREATE USER <schema_name> IDENTIFIED BY <password>;
```
Note that you will need appropriate privileges to create a user/schema.
If the schema does exist and you are still receiving this error, make sure that you are connecting to the correct database and that the schema is not locked or inaccessible. You can also check the spelling and case of the schema name to ensure that it matches exactly.