oracle中with的用法

with 子句在 oracle 中创建临时表或视图，用于创建复杂的临时表或视图，重命名查询结果并提高查询性能：创建临时表：with clause_name as (subquery)重命名查询结果：with clause_name as (subquery)提高查询性能：将子查询存储在临时表中提升性能

WITH 子句在 Oracle 中的用法

什么是 WITH 子句？

WITH 子句在 Oracle 中用于创建临时表或视图，这些表或视图仅在当前会话中可见。

语法

WITH clause_name AS (subquery)
SELECT ...
FROM ...

• clause_name：临时表或视图的名称。
• subquery：查询语句，用于创建临时表或视图。

用法

WITH 子句通常用于以下场景：

• 创建复杂的临时表或视图，用于查询中。
• 将复杂查询的结果重命名为更简单的名称，便于后续引用。
• 提高查询性能，通过将子查询的结果存储在临时表中。

示例

创建临时表

WITH EmployeeTemp AS (
  SELECT employee_id, salary, department_id
  FROM Employees
  WHERE salary > 10000
)
SELECT * FROM EmployeeTemp;

重命名查询结果

WITH EmployeeSalaries AS (
  SELECT employee_id, salary
  FROM Employees
)
SELECT employee_id, salary AS emp_salary
FROM EmployeeSalaries;

提高查询性能

WITH EmployeeAvgSalary AS (
  SELECT department_id, AVG(salary) AS avg_salary
  FROM Employees
  GROUP BY department_id
)
SELECT * FROM EmployeeAvgSalary
WHERE avg_salary > 50000;

以上就是oracle中with的用法的详细内容，更多请关注编程网其它相关文章！