如何在 MySQL 中使用“ WITH”子句？

我正在将所有的 SQLServer 查询转换为 MySQL，并且在其中包含 WITH的查询都失败了。这里有一个例子:

WITH t1 AS
(
SELECT article.*, userinfo.*, category.*
FROM question
INNER JOIN userinfo ON userinfo.user_userid = article.article_ownerid
INNER JOIN category ON article.article_categoryid = category.catid
WHERE article.article_isdeleted = 0
)
SELECT t1.*
FROM t1
ORDER BY t1.article_date DESC
LIMIT 1, 3
304142 次浏览
小开

在 Sql 中，with 语句指定一个临时命名的结果集，称为公共表表达式(CTE)。它可以用于递归查询，但在本例中，它指定为子集。如果 mysql 允许子选项，我会尝试

select t1.*
from  (
SELECT  article.*,
userinfo.*,
category.*
FROM    question INNER JOIN
userinfo ON userinfo.user_userid=article.article_ownerid INNER JOIN category ON article.article_categoryid=category.catid
WHERE   article.article_isdeleted = 0
) t1
ORDER BY t1.article_date DESC Limit 1, 3
小开

该特性称为公共表表达式 Http://msdn.microsoft.com/en-us/library/ms190766.aspx

你不能在 mySQL 中做同样的事情，最简单的方法可能是创建一个反映 CTE 的视图，然后从视图中进行选择。您可以使用子查询来完成这项工作，但是它的性能会非常糟糕。如果遇到任何执行递归的 CTE，我不知道如何在不使用存储过程的情况下重新创建它。

编辑: 正如我在评论中所说，您发布的示例不需要 CTE，因此您必须简化它，因为它可以写成

SELECT article.*, userinfo.*, category.* FROM question
INNER JOIN userinfo ON userinfo.user_userid=article.article_ownerid
INNER JOIN category ON article.article_categoryid=category.catid
WHERE article.article_isdeleted = 0
ORDER BY article_date DESC Limit 1, 3
小开
最佳答案

8.0版本之前的 MySQL 不支持 WITH子句 (SQL Server 术语中的 CTE; Oracle 中的子查询因子分解) ，因此您只能使用:

  • 临时表
  • 派生表
  • 内联视图(有效地表示 WITH子句——它们是可互换的)

这个专题的要求可以追溯到2006年。

如前所述，您提供了一个糟糕的示例——如果不以任何方式改变列的输出，就不需要执行子选择:

  SELECT *
FROM ARTICLE t
JOIN USERINFO ui ON ui.user_userid = t.article_ownerid
JOIN CATEGORY c ON c.catid =  t.article_categoryid
WHERE t.published_ind = 0
ORDER BY t.article_date DESC
LIMIT 1, 3

这里有一个更好的例子:

SELECT t.name,
t.num
FROM TABLE t
JOIN (SELECT c.id
COUNT(*) 'num'
FROM TABLE c
WHERE c.column = 'a'
GROUP BY c.id) ta ON ta.id = t.id
小开

“公共表表达式”功能在 MySQL 中不可用，所以必须创建一个视图或临时表来解决，这里我使用了一个临时表。

这里提到的存储过程将解决您的需要。如果要获取所有团队成员及其关联成员，此存储过程将有所帮助:

----------------------------------
user_id   |   team_id
----------------------------------
admin     |   NULL
ramu      |   admin
suresh    |   admin
kumar     |   ramu
mahesh    |   ramu
randiv    |   suresh
-----------------------------------

密码:

DROP PROCEDURE `user_hier`//
CREATE DEFINER=`root`@`localhost` PROCEDURE `user_hier`(in team_id varchar(50))
BEGIN
declare count int;
declare tmp_team_id varchar(50);
CREATE TEMPORARY TABLE res_hier(user_id varchar(50),team_id varchar(50))engine=memory;
CREATE TEMPORARY TABLE tmp_hier(user_id varchar(50),team_id varchar(50))engine=memory;
set tmp_team_id = team_id;
SELECT COUNT(*) INTO count FROM user_table WHERE user_table.team_id=tmp_team_id;
WHILE count>0 DO
insert into res_hier select user_table.user_id,user_table.team_id from user_table where user_table.team_id=tmp_team_id;
insert into tmp_hier select user_table.user_id,user_table.team_id from user_table where user_table.team_id=tmp_team_id;
select user_id into tmp_team_id from tmp_hier limit 0,1;
select count(*) into count from tmp_hier;
delete from tmp_hier where user_id=tmp_team_id;
end while;
select * from res_hier;
drop temporary table if exists res_hier;
drop temporary table if exists tmp_hier;
end

这可以被称为:

mysql>call user_hier ('admin')//
小开

Mysql 开发者团队宣布8.0版本将会有 MySQL 中的公共表表达式(CTE)，因此可以编写这样的查询:


用递归方法
(
选择1作为 n
工会
从 my _ cte 中选择1 + n，其中 n < 10
)
选择 * FROM my _ cte;
+------+
我不知道
+------+
我不知道
我不知道
我不知道
我不知道
我不知道
我不知道
我不知道
我不知道
我不知道
10分钟
+------+
设置10行(0,00秒)

小开

我点击了 Lisachenko 分享的链接，找到了这个博客的另一个链接: Http://guilhembichot.blogspot.co.uk/2013/11/with-recursive-and-mysql.html

本文介绍了模拟 SQLWITH2种用法的方法。很好地解释了这些工具如何执行与 SQLWith 类似的查询。

1)使用 WITH，这样您就不必多次执行相同的子查询

CREATE VIEW D AS (SELECT YEAR, SUM(SALES) AS S FROM T1 GROUP BY YEAR);
SELECT D1.YEAR, (CASE WHEN D1.S>D2.S THEN 'INCREASE' ELSE 'DECREASE' END) AS TREND
FROM
D AS D1,
D AS D2
WHERE D1.YEAR = D2.YEAR-1;
DROP VIEW D;

2)递归查询可以通过一个存储过程来完成，该存储过程使得调用类似于带查询的递归调用。

CALL WITH_EMULATOR(
"EMPLOYEES_EXTENDED",
"
SELECT ID, NAME, MANAGER_ID, 0 AS REPORTS
FROM EMPLOYEES
WHERE ID NOT IN (SELECT MANAGER_ID FROM EMPLOYEES WHERE MANAGER_ID IS NOT NULL)
",
"
SELECT M.ID, M.NAME, M.MANAGER_ID, SUM(1+E.REPORTS) AS REPORTS
FROM EMPLOYEES M JOIN EMPLOYEES_EXTENDED E ON M.ID=E.MANAGER_ID
GROUP BY M.ID, M.NAME, M.MANAGER_ID
",
"SELECT * FROM EMPLOYEES_EXTENDED",
0,
""
);

这是代码或存储过程

# Usage: the standard syntax:
#   WITH RECURSIVE recursive_table AS
#    (initial_SELECT
#     UNION ALL
#     recursive_SELECT)
#   final_SELECT;
# should be translated by you to
# CALL WITH_EMULATOR(recursive_table, initial_SELECT, recursive_SELECT,
#                    final_SELECT, 0, "").


# ALGORITHM:
# 1) we have an initial table T0 (actual name is an argument
# "recursive_table"), we fill it with result of initial_SELECT.
# 2) We have a union table U, initially empty.
# 3) Loop:
#   add rows of T0 to U,
#   run recursive_SELECT based on T0 and put result into table T1,
#   if T1 is empty
#      then leave loop,
#      else swap T0 and T1 (renaming) and empty T1
# 4) Drop T0, T1
# 5) Rename U to T0
# 6) run final select, send relult to client


# This is for *one* recursive table.
# It would be possible to write a SP creating multiple recursive tables.


delimiter |


CREATE PROCEDURE WITH_EMULATOR(
recursive_table varchar(100), # name of recursive table
initial_SELECT varchar(65530), # seed a.k.a. anchor
recursive_SELECT varchar(65530), # recursive member
final_SELECT varchar(65530), # final SELECT on UNION result
max_recursion int unsigned, # safety against infinite loop, use 0 for default
create_table_options varchar(65530) # you can add CREATE-TABLE-time options
# to your recursive_table, to speed up initial/recursive/final SELECTs; example:
# "(KEY(some_column)) ENGINE=MEMORY"
)


BEGIN
declare new_rows int unsigned;
declare show_progress int default 0; # set to 1 to trace/debug execution
declare recursive_table_next varchar(120);
declare recursive_table_union varchar(120);
declare recursive_table_tmp varchar(120);
set recursive_table_next  = concat(recursive_table, "_next");
set recursive_table_union = concat(recursive_table, "_union");
set recursive_table_tmp   = concat(recursive_table, "_tmp");
# Cleanup any previous failed runs
SET @str =
CONCAT("DROP TEMPORARY TABLE IF EXISTS ", recursive_table, ",",
recursive_table_next, ",", recursive_table_union,
",", recursive_table_tmp);
PREPARE stmt FROM @str;
EXECUTE stmt;
# If you need to reference recursive_table more than
# once in recursive_SELECT, remove the TEMPORARY word.
SET @str = # create and fill T0
CONCAT("CREATE TEMPORARY TABLE ", recursive_table, " ",
create_table_options, " AS ", initial_SELECT);
PREPARE stmt FROM @str;
EXECUTE stmt;
SET @str = # create U
CONCAT("CREATE TEMPORARY TABLE ", recursive_table_union, " LIKE ", recursive_table);
PREPARE stmt FROM @str;
EXECUTE stmt;
SET @str = # create T1
CONCAT("CREATE TEMPORARY TABLE ", recursive_table_next, " LIKE ", recursive_table);
PREPARE stmt FROM @str;
EXECUTE stmt;
if max_recursion = 0 then
set max_recursion = 100; # a default to protect the innocent
end if;
recursion: repeat
# add T0 to U (this is always UNION ALL)
SET @str =
CONCAT("INSERT INTO ", recursive_table_union, " SELECT * FROM ", recursive_table);
PREPARE stmt FROM @str;
EXECUTE stmt;
# we are done if max depth reached
set max_recursion = max_recursion - 1;
if not max_recursion then
if show_progress then
select concat("max recursion exceeded");
end if;
leave recursion;
end if;
# fill T1 by applying the recursive SELECT on T0
SET @str =
CONCAT("INSERT INTO ", recursive_table_next, " ", recursive_SELECT);
PREPARE stmt FROM @str;
EXECUTE stmt;
# we are done if no rows in T1
select row_count() into new_rows;
if show_progress then
select concat(new_rows, " new rows found");
end if;
if not new_rows then
leave recursion;
end if;
# Prepare next iteration:
# T1 becomes T0, to be the source of next run of recursive_SELECT,
# T0 is recycled to be T1.
SET @str =
CONCAT("ALTER TABLE ", recursive_table, " RENAME ", recursive_table_tmp);
PREPARE stmt FROM @str;
EXECUTE stmt;
# we use ALTER TABLE RENAME because RENAME TABLE does not support temp tables
SET @str =
CONCAT("ALTER TABLE ", recursive_table_next, " RENAME ", recursive_table);
PREPARE stmt FROM @str;
EXECUTE stmt;
SET @str =
CONCAT("ALTER TABLE ", recursive_table_tmp, " RENAME ", recursive_table_next);
PREPARE stmt FROM @str;
EXECUTE stmt;
# empty T1
SET @str =
CONCAT("TRUNCATE TABLE ", recursive_table_next);
PREPARE stmt FROM @str;
EXECUTE stmt;
until 0 end repeat;
# eliminate T0 and T1
SET @str =
CONCAT("DROP TEMPORARY TABLE ", recursive_table_next, ", ", recursive_table);
PREPARE stmt FROM @str;
EXECUTE stmt;
# Final (output) SELECT uses recursive_table name
SET @str =
CONCAT("ALTER TABLE ", recursive_table_union, " RENAME ", recursive_table);
PREPARE stmt FROM @str;
EXECUTE stmt;
# Run final SELECT on UNION
SET @str = final_SELECT;
PREPARE stmt FROM @str;
EXECUTE stmt;
# No temporary tables may survive:
SET @str =
CONCAT("DROP TEMPORARY TABLE ", recursive_table);
PREPARE stmt FROM @str;
EXECUTE stmt;
# We are done :-)
END|


delimiter ;
小开

我喜欢这个 线中@Brad 的回答，但是想要一种方法来保存结果以便进一步处理(MySql 8) :

-- May need to adjust the recursion depth first
SET @@cte_max_recursion_depth = 10000 ; -- permit deeper recursion


-- Some boundaries
set @startDate = '2015-01-01'
, @endDate = '2020-12-31' ;


-- Save it to a table for later use
drop table if exists tmpDates ;
create temporary table tmpDates as      -- this has to go _before_ the "with", Duh-oh!
WITH RECURSIVE t as (
select @startDate as dt
UNION
SELECT DATE_ADD(t.dt, INTERVAL 1 DAY) FROM t WHERE DATE_ADD(t.dt, INTERVAL 1 DAY) <= @endDate
)
select * FROM t     -- need this to get the "with"'s results as a "result set", into the "create"
;


-- Exists?
select * from tmpDates ;

结果是:

dt        |
----------|
2015-01-01|
2015-01-02|
2015-01-03|
2015-01-04|
2015-01-05|
2015-01-06|

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