作者：杨涛涛
资深数据库专家，专研 MySQL 十余年。擅长 MySQL、PostgreSQL、MongoDB 等开源数据库相关的备份恢复、SQL 调优、监控运维、高可用架构设计等。目前任职于爱可生，为各大运营商及银行金融企业提供 MySQL 相关技术支持、MySQL 相关课程培训等工作。
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MySQL 8.0 发布已经好几年了，之前介绍过 WITH 语句（通用表达式）的简单用途以及使用场景，类似如下的语句：

with tmp(a) as (select 1 union all select 2) select * from tmp;

正巧之前客户就咨询我，WITH 有没有可能和 UPDATE、DELETE 等语句一起来用？或者说有没有可以简化日常 SQL 的其他用法，有点迷惑，能否写几个例子简单说明下？

其实 WITH 表达式除了和 SELECT 一起用， 还可以有下面的组合：

insert with 、with update、with delete、with with、with recursive(可以模拟数字、日期等序列)、WITH 可以定义多张表

我们来一个一个看看：

1. 用 WITH 表达式来造数据

用 WITH 表达式来造数据，非常简单，比如下面例子：给表 y1 添加100条记录，日期字段要随机。

localhost:ytt>create table y1 (id serial primary key, r1 int,log_date date); Query OK, 0 rows affected (0.09 sec) localhost:ytt>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 100) TABLE tmp; Query OK, 100 rows affected (0.03 sec) Records: 100 Duplicates: 0 Warnings: 0 localhost:ytt>table y1 limit 10; +----+------+------------+ | id | r1 | log_date | +----+------+------------+ | 1 | 1 | 2021-04-20 | | 2 | 8 | 2020-04-02 | | 3 | 5 | 2019-05-26 | | 4 | 1 | 2018-01-21 | | 5 | 2 | 2016-09-08 | | 6 | 9 | 2016-06-14 | | 7 | 7 | 2016-02-06 | | 8 | 6 | 2014-03-18 | | 9 | 6 | 2011-08-25 | | 10 | 9 | 2010-02-02 | +----+------+------------+ 10 rows in set (0.00 sec)

2. 用 WITH 表达式来更新表数据

WITH 表达式可以与 UPDATE 语句一起，来执行要更新的表记录：

localhost:ytt>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 < 100) -> UPDATE -> tmp AS a, -> y1 AS b -> SET -> b.r1 = a.b -> WHERE a.a = b.id; Query OK, 49 rows affected (0.02 sec) Rows matched: 50 Changed: 49 Warnings: 0 localhost:ytt>table y1 limit 10; +----+------+------------+ | id | r1 | log_date | +----+------+------------+ | 1 | 1 | 2021-04-20 | | 2 | 8 | 2019-12-26 | | 3 | 100 | 2018-06-12 | | 4 | 8 | 2017-07-11 | | 5 | 100 | 2016-08-10 | | 6 | 9 | 2015-09-14 | | 7 | 100 | 2014-12-19 | | 8 | 2 | 2014-08-13 | | 9 | 100 | 2014-08-05 | | 10 | 8 | 2011-11-12 | +----+------+------------+ 10 rows in set (0.00 sec)

3. 用 WITH 表达式来删除表数据

比如删除 ID 为奇数的行，可以用 WITH DELETE 形式的删除语句：

localhost:ytt>WITH recursive tmp (a) AS -> (SELECT -> 1 -> UNION -> ALL -> SELECT -> a + 2 -> FROM -> tmp -> WHERE a < 100) -> DELETE FROM y1 WHERE id IN (TABLE tmp); Query OK, 50 rows affected (0.02 sec) localhost:ytt>table y1 limit 10; +----+------+------------+ | id | r1 | log_date | +----+------+------------+ | 2 | 6 | 2019-05-16 | | 4 | 8 | 2015-12-07 | | 6 | 2 | 2014-05-14 | | 8 | 7 | 2010-05-07 | | 10 | 3 | 2007-03-27 | | 12 | 6 | 2006-12-14 | | 14 | 3 | 2004-04-22 | | 16 | 7 | 2001-09-16 | | 18 | 7 | 2001-01-04 | | 20 | 7 | 2000-02-12 | +----+------+------------+ 10 rows in set (0.00 sec)

与 DELETE 一起使用，要注意一点：WITH 表达式本身数据为只读，所以多表 DELETE 中不能包含 WITH 表达式。比如把上面的语句改成多表删除形式会直接报 WITH 表达式不可更新的错误。

localhost:ytt>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 1288 (HY000): The target table b of the DELETE is not updatable

4. WITH 和 WITH 一起用

前提条件：WITH 表达式不能在同一个层级，一个层级只允许一个 WITH 表达式

localhost:ytt>SELECT * FROM -> ( -> WITH tmp1 (a, b, c) AS -> ( -> VALUES -> ROW (1, 2, 3), -> ROW (3, 4, 5), -> ROW (6, 7, 8) -> ) SELECT * FROM -> ( -> WITH tmp2 (d, e, f) AS ( -> VALUES -> ROW (100, 200, 300), -> ROW (400, 500, 600) -> ) TABLE tmp2 -> ) X -> JOIN tmp1 Y -> ) Z ORDER BY a; +-----+-----+-----+---+---+---+ | d | e | f | a | b | c | +-----+-----+-----+---+---+---+ | 400 | 500 | 600 | 1 | 2 | 3 | | 100 | 200 | 300 | 1 | 2 | 3 | | 400 | 500 | 600 | 3 | 4 | 5 | | 100 | 200 | 300 | 3 | 4 | 5 | | 400 | 500 | 600 | 6 | 7 | 8 | | 100 | 200 | 300 | 6 | 7 | 8 | +-----+-----+-----+---+---+---+ 6 rows in set (0.01 sec)

5. WITH 多个表达式来 JOIN

用上面的例子，改写多个 WITH 为一个 WITH：

localhost:ytt>WITH -> tmp1 (a, b, c) AS -> ( -> VALUES -> ROW (1, 2, 3), -> ROW (3, 4, 5), -> ROW (6, 7, 8) -> ), -> tmp2 (d, e, f) AS ( -> VALUES -> ROW (100, 200, 300), -> ROW (400, 500, 600) -> ) -> SELECT * FROM tmp2,tmp1 ORDER BY a; +-----+-----+-----+---+---+---+ | d | e | f | a | b | c | +-----+-----+-----+---+---+---+ | 400 | 500 | 600 | 1 | 2 | 3 | | 100 | 200 | 300 | 1 | 2 | 3 | | 400 | 500 | 600 | 3 | 4 | 5 | | 100 | 200 | 300 | 3 | 4 | 5 | | 400 | 500 | 600 | 6 | 7 | 8 | | 100 | 200 | 300 | 6 | 7 | 8 | +-----+-----+-----+---+---+---+ 6 rows in set (0.00 sec)

6. with 生成日期序列

用 WITH 表达式生成日期序列，类似于 POSTGRESQL 的 generate_series 表函数，比如，从 ‘2020-01-01’ 开始，生成一个月的日期序列：

localhost:ytt>WITH recursive seq_date (log_date) AS -> (SELECT -> '2020-01-01' -> UNION -> ALL -> SELECT -> log_date + INTERVAL 1 DAY -> FROM -> seq_date -> WHERE log_date + INTERVAL 1 DAY < '2020-02-01') -> SELECT -> log_date -> FROM -> seq_date; +------------+ | log_date | +------------+ | 2020-01-01 | | 2020-01-02 | | 2020-01-03 | | 2020-01-04 | | 2020-01-05 | | 2020-01-06 | | 2020-01-07 | | 2020-01-08 | | 2020-01-09 | | 2020-01-10 | | 2020-01-11 | | 2020-01-12 | | 2020-01-13 | | 2020-01-14 | | 2020-01-15 | | 2020-01-16 | | 2020-01-17 | | 2020-01-18 | | 2020-01-19 | | 2020-01-20 | | 2020-01-21 | | 2020-01-22 | | 2020-01-23 | | 2020-01-24 | | 2020-01-25 | | 2020-01-26 | | 2020-01-27 | | 2020-01-28 | | 2020-01-29 | | 2020-01-30 | | 2020-01-31 | +------------+ 31 rows in set (0.00 sec)

7. with 表达式做派生表

使用刚才那个日期列表，

localhost:ytt>SELECT -> * -> FROM -> ( -> WITH recursive seq_date (log_date) AS -> (SELECT -> '2020-01-01' -> UNION -> ALL -> SELECT -> log_date + INTERVAL 1 DAY -> FROM -> seq_date -> WHERE log_date+ interval 1 day < '2020-02-01') -> select * -> FROM -> seq_date -> ) X -> LIMIT 10; +------------+ | log_date | +------------+ | 2020-01-01 | | 2020-01-02 | | 2020-01-03 | | 2020-01-04 | | 2020-01-05 | | 2020-01-06 | | 2020-01-07 | | 2020-01-08 | | 2020-01-09 | | 2020-01-10 | +------------+ 10 rows in set (0.00 sec)

WITH 表达式使用非常灵活，不同的场景可以有不同的写法，的确可以简化日常 SQL 的编写。