sql中with as用法以及with-as性能调优/with用法举例

WITH cte_name1[(column_name_list)] AS (inner_query_definition_1)
   [,cte_name2[(column_name_list)] AS (inner_query_definition_2)]
[,...]
outer_query_definition

示例：
-- 单个子查询
with tmp as(select username,userage from user)
select username from tmp

-- 多个子查询  多个CTE 之间加，分割
with tmp1 as (select * from father),
     tmp2 as (select * from child)
select * from temp1,temp2 on tmp1.id = tmp2.parentId

CREATE TABLE user(
    id INT NOT NULL PRIMARY KEY,
    sex CHAR(3),NAME CHAR(20)
);

INSERT INTO user VALUES 
(1,'nan','陈一'),
(2,'nv','珠二'),
(3,'nv','张三'),
(4,'nan','李四'),
(5,'nv','王五'),
(6,'nan','赵六');
  
# 定义CTE，顺便为每列重新命名，且使用ORDER BY子句
WITH nv_user(myid,mysex,myname) AS (
    SELECT * FROM user WHERE sex='nv' ORDER BY id DESC
)
# 使用CTE
SELECT * FROM nv_user;
+------+-------+-------------+
| myid | mysex | myname      |
+------+-------+-------------+
|    5 | nv    | 王五        |
|    3 | nv    | 张三        |
|    2 | nv    | 珠二        |
+------+-------+-------------+

# 多次引用，避免重复书写
WITH nv_t(myid,mysex,myname) AS (
    SELECT * FROM user WHERE sex='nv'
)
SELECT t1.*,t2.*
FROM nv_t t1 JOIN nv_t t2
WHERE t1.myid = t2.myid+1;
  
# 多次定义，避免派生表嵌套
WITH
nv_t1 AS (          /* 第一个CTE */
    SELECT * FROM user WHERE sex='nv'
),
nv_t2 AS (          /* 第二个CTE */
    SELECT * FROM nv_t1 WHERE id>3
)
SELECT * FROM nv_t2;

SELECT * FROM
(SELECT * FROM
(SELECT * FROM user WHERE sex='nv') AS nv_t1) AS nv_t2;

with
sql1 as (select  s_name from test_tempa),  
sql2 as (select  s_name from test_tempb where not exists (select s_name from sql1 where rownum=1))  

select * from sql1
union all
select * from sql2
union all
select ‘no records' from dual
where not exists (select s_name from sql1 where rownum=1)  
and not exists (select s_name from sql2 where rownum=1); 

-- 分类表
CREATE TABLE category ( cid VARCHAR ( 32 ) PRIMARY KEY, cname VARCHAR ( 50 ) );

-- 商品表
CREATE TABLE products (
	pid VARCHAR ( 32 ) PRIMARY KEY,
	pname VARCHAR ( 50 ),
	price INT,
	category_id VARCHAR ( 32 ),
	FOREIGN KEY ( category_id ) REFERENCES category ( cid ) 
);
-- 分类数据
INSERT INTO category(cid,cname) VALUES('c001','家电');
INSERT INTO category(cid,cname) VALUES('c002','鞋服');
INSERT INTO category(cid,cname) VALUES('c003','化妆品');
INSERT INTO category(cid,cname) VALUES('c004','汽车');

-- 商品数据
INSERT INTO products(pid, pname,price,category_id) VALUES('p001','小米电视机',5000,'c001');
INSERT INTO products(pid, pname,price,category_id) VALUES('p002','格力空调',3000,'c001');
INSERT INTO products(pid, pname,price,category_id) VALUES('p003','美的冰箱',4500,'c001');
INSERT INTO products (pid, pname,price,category_id) VALUES('p004','篮球鞋',800,'c002');
INSERT INTO products (pid, pname,price,category_id) VALUES('p005','运动裤',200,'c002');
INSERT INTO products (pid, pname,price,category_id) VALUES('p006','T恤',300,'c002');
INSERT INTO products (pid, pname,price,category_id) VALUES('p007','冲锋衣',2000,'c002');
INSERT INTO products (pid, pname,price,category_id) VALUES('p008','神仙水',800,'c003');
INSERT INTO products (pid, pname,price,category_id) VALUES('p009','大宝',200,'c003');

select * from category c
left join products p on c.cid = p.category_id
where c.cname = '家电' and p.pname in ('格力空调','美的冰箱');

with c as (select * from category where cname = '家电'),
     p as (select * from products where pname in ('格力空调','美的冰箱'))
select * from c,p where c.cid = p.category_id;

with tem as (select avg(price) as houseElecAvg from products p
			left join category c on c.cid = p.category_id
			where c.cname = '家电'),
	tem1 as (select max(p1.price),min(p1.price) from products p1)
select * from tem,tem1;

insert into table2
with
    s1 as (select rownum c1 from dual connect by rownum <= 10),
    s2 as (select rownum c2 from dual connect by rownum <= 10)
select a.c1, b.c2 from s1 a, s2 b where...;

with recursive cte_name as (
    select_statement_1       /* 该cte_body称为定位点成员 */
  union [all]
    cte_usage_statement      /* 此处引用cte自身，称为递归成员 */
)
outer_definition_statement    /* 对递归CTE的查询，称为递归查询 */

# n迭代次数
with RECURSIVE c(n) as
 (select 1   union all select n + 1 from c where n < 10)
select n from c;

+------+
| 	 n |
+------+
|    1 |
|    2 |
|    3 |
|    4 |
|    5 |
|    6 |
|    7 |
|    8 |
|    9 |
|   10 |
+------+
10 rows in set (0.00 sec)

-- 创建测试表
create table y1 (id serial primary key, r1 int,log_date date);

-- 插入数据
INSERT y1 (r1,log_date)
   WITH recursive tmp (a, b) AS
   (SELECT
     1,
     '2021-04-20'
   UNION
   ALL
   SELECT
     ROUND(RAND() * 10),
     b - INTERVAL ROUND(RAND() * 1000) DAY
   FROM
     tmp
   LIMIT 10)
select * from  tmp;

WITH recursive tmp (a, b, c) AS
    (SELECT
      1,
      1,
      '2021-04-20'
    UNION ALL
    SELECT
      a + 2,
      100,
      DATE_SUB(
        CURRENT_DATE(),
        INTERVAL ROUND(RAND() * 1000, 0) DAY
      )
    FROM
      tmp
    WHERE a < 10)
UPDATE
     tmp AS a,
     y1 AS b
   SET
     b.r1 = a.b
   WHERE a.a = b.id;

WITH recursive tmp (a) AS
    (SELECT
      1
    UNION
    ALL
    SELECT
      a + 2
    FROM
      tmp
    WHERE a < 10)
    DELETE FROM y1 WHERE id IN (select * from tmp);

WITH recursive tmp (a) AS
     (SELECT
       1
     UNION
     ALL
     SELECT
       a + 2
     FROM
       tmp
     WHERE a < 100)
     delete a,b from y1 a join tmp b where a.id = b.a;

error: [HY000][1288] The target table b of the DELETE is not updatable

WITH recursive seq_date (log_date) AS
      (SELECT
        '2023-07-09'
      UNION
      ALL
      SELECT
        log_date + INTERVAL 1 DAY
      FROM
        seq_date
      WHERE log_date + INTERVAL 1 DAY < '2023-07-20')
      SELECT
        log_date
      FROM
        seq_date;

+-----------+
|   log_date| 
+-----------+
| 2023-07-09|
| 2023-07-10| 
| 2023-07-11| 
| 2023-07-12| 
| 2023-07-13| 
| 2023-07-14| 
| 2023-07-15| 
| 2023-07-16| 
| 2023-07-17| 
| 2023-07-18| 
| 2023-07-19| 
+------+