WITH 子句在Oracle 中建立臨時表或視圖，用於建立複雜的臨時表或視圖，重新命名查詢結果並提高查詢效能：建立臨時表：WITH clause_name AS (subquery)重命名查詢結果：WITH clause_name AS (subquery)提高查詢效能：將子查詢儲存在臨時表中提升效能
WITH 子句在Oracle 中的用法
什麼是WITH 子句？
WITH 子句在 Oracle 中用於建立臨時表或視圖，這些表或視圖僅在目前會話中可見。
語法
<code>WITH clause_name AS (subquery) SELECT ... FROM ...</code>
clause_name：暫存資料表或檢視的名稱。 subquery：查詢語句，用於建立臨時表或檢視。 用法
WITH 子句通常用於以下場景：
範例
建立臨時表
<code>WITH EmployeeTemp AS ( SELECT employee_id, salary, department_id FROM Employees WHERE salary > 10000 ) SELECT * FROM EmployeeTemp;</code>
重命名查詢結果
<code>WITH EmployeeSalaries AS ( SELECT employee_id, salary FROM Employees ) SELECT employee_id, salary AS emp_salary FROM EmployeeSalaries;</code>
提高查詢效能
<code>WITH EmployeeAvgSalary AS ( SELECT department_id, AVG(salary) AS avg_salary FROM Employees GROUP BY department_id ) SELECT * FROM EmployeeAvgSalary WHERE avg_salary > 50000;</code>
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