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mysql

dependent subquery 需要引起最大关注，可谓是性能杀手，无数开发着已经踩坑。

mysql 8 实现了 cte，并且实现了 with recursive ，很强大的功能。 with recursive tmp(n) as ( select 1 union all select n+1 from tmp where 1=1 and n<=10 ) select * from tmp ; +------+ | n | +------+ | 1 | | 2 | | 3 | | 4 | | 5 | | 6 | |

os: centos 7.4.1708 db: mysql 8.0.20 help explain mysql> help explain; Name: 'EXPLAIN' Description: Syntax: {EXPLAIN | DESCRIBE | DESC} tbl_name [col_name | wild] {EXPLAIN | DESCRIBE | DESC} [explain_type] {explainable_stmt | FOR CONNECTION

os: centos 7.4.1708 db: mysql 8.0.20 版本 # cat /etc/centos-release CentOS Linux release 7.4.1708 (Core) # # # yum list installed |grep -i mysql80 mysql-community-client.x86_64 8.0.20-1.el7 @mysql80-community mysql-community-co

https://developer.aliyun.com/article/768447?spm=a2c6h.12873581.0.0.3a8d51be8iN9Go&groupCode=database

mysql 的列转行想找个函数，但是没有找到 目前是通过有条件的笛卡尔积完成的。 DROP IF EXISTS TABLE pyb_tmp_160315_2 CREATE TABLE pyb_tmp_160315_2 ( id INT, NAME VARCHAR(200) ) ; INSERT INTO pyb_tmp_16

mysql 的行转列 主要是通过group_concat 来实现。 CREATE TABLE pyb_tmp_160315 ( id INT, NAME VARCHAR(200) ) ; INSERT INTO pyb_tmp_160315 VALUES(1,'a'),(1,'b'),(2,'a'),(2,'b'),(2,'c') ;

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