PostgreSQL-WITH AS短語

WITH提供了一種方式來書寫在一個大型查詢中使用的輔助語句。這些語句通常被稱為公共表表達式或CTE，
它們可以被看成是定義只在一個查詢中存在的臨時表。在WITH子句中的每一個輔助語句可以是一個SELECT、INSERT、UPDATE或DELETE，
並且WITH子句本身也可以被附加到一個主語句，主語句也可以是SELECT、INSERT、UPDATE或DELETE。

WITH regional_sales AS (
    SELECT region, SUM(amount) AS total_sales
    FROM orders
    GROUP BY region
), top_regions AS (
    SELECT region
    FROM regional_sales
    WHERE total_sales > (SELECT SUM(total_sales)/10 FROM regional_sales)
)
SELECT region,
       product,
       SUM(quantity) AS product_units,
       SUM(amount) AS product_sales
FROM orders
WHERE region IN (SELECT region FROM top_regions)
GROUP BY region, product;

 

 

with語句與全連接

WITH RECURSIVE included_parts(sub_part, part, quantity) AS (
    SELECT sub_part, part, quantity FROM parts WHERE part = 'our_product'
  UNION ALL
    SELECT p.sub_part, p.part, p.quantity
    FROM included_parts pr, parts p
    WHERE p.part = pr.sub_part
)
SELECT sub_part, SUM(quantity) as total_quantity
FROM included_parts
GROUP BY sub_part

 

 創建表、插入數據

--DROP TABLE COMPANY;
CREATE TABLE COMPANY(
   ID INT PRIMARY KEY     NOT NULL,
   NAME           TEXT    NOT NULL,
   AGE            INT     NOT NULL,
   ADDRESS        CHAR(50),
   SALARY         REAL
);
INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (1, 'Paul', 32, 'California', 20000.00 );

INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (2, 'Allen', 25, 'Texas', 15000.00 );

INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (3, 'Teddy', 23, 'Norway', 20000.00 );

INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (4, 'Mark', 25, 'Rich-Mond ', 65000.00 );

INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (5, 'David', 27, 'Texas', 85000.00 );

INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (6, 'Kim', 22, 'South-Hall', 45000.00 );

INSERT INTO COMPANY VALUES (7, 'James', 24, 'Houston', 10000.00 );

 

接下來讓我們使用 RECURSIVE 關鍵字和 WITH 子句編寫一個查詢，查找 SALARY(工資) 字段小於 20000 的數據並計算它們的和：

WITH RECURSIVE t(n) AS ( VALUES (0) UNION ALL SELECT SALARY FROM COMPANY WHERE SALARY < 20000 ) SELECT sum(n) FROM t;

 

建立一張和 COMPANY 表相似的 COMPANY1 表，使用 DELETE 語句和 WITH 子句刪除 COMPANY 表中 SALARY(工資) 字段大於等於 30000 的數據，並將刪除的數據插入 COMPANY1 表，實現將 COMPANY 表數據轉移到 COMPANY1 表中：

CREATE TABLE COMPANY1(
   ID INT PRIMARY KEY     NOT NULL,
   NAME           TEXT    NOT NULL,
   AGE            INT     NOT NULL,
   ADDRESS        CHAR(50),
   SALARY         REAL
);

--刪除 COMPANY 表中 SALARY(工資) 字段大於等於 30000 的數據，

WITH moved_rows AS ( DELETE FROM COMPANY WHERE SALARY >= 30000 RETURNING * )

--並將刪除的數據插入 COMPANY1 表
INSERT INTO COMPANY1 (SELECT * FROM moved_rows);

 

 

 

本文參考：https://blog.csdn.net/freshman2020/article/details/110551342?utm_medium=distribute.pc_relevant.none-task-blog-baidujs_title-0&spm=1001.2101.3001.4242