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MySQL union 语句，中文查不到数据

问题描述

MySQL 8.0.32 union 语句，中文查不到数据

解决问题思路

1、Create a table `test` with two fields, such as id and name

mysql>create table test ( id int unsigned auto_increment key, name varchar(50))ENGINE=INNODB;

2、Insert data into the table. The name field is Chinese characters, such as "姜志福"

mysql>insert into test(id,name) values(1,'姜志福');

3、Use the union statement to query, such as：

select * from (

select * from test

union all

select * from test

)a where id = 1 and name = '姜志福'

最终排查为这是MySQL BUG

https://bugs.mysql.com/bug.php?id=110005

临时解决可以关闭 derived_condition_pushdown 特性

set optimizer_switch='derived_condition_pushdown=off';

https://dev.mysql.com/doc/relnotes/mysql/8.0/en/news-8-0-32.html

A condition pushdown into a UNION of queries having LIKE clauses did not preserve the correct character set, leading to an (erroneous) empty result.

We solve this problem in two parts:

By refactoring resolution of LIKE expressions, in which character set determination and propagation were previously performed in two separate blocks of the code that were not always consistent with one another.

By adding, in the internal parse_expression() function, a character set prefix to any literal character string that is cloned.

(Bug #107787, Bug #34359297, Bug #34589153)

https://dev.mysql.com/doc/relnotes/mysql/8.0/en/news-8-0-33.html

When cloning a condition to push down to a derived table, characters in strings representing conditions were converted to utfmb4 correctly only for values less than 128 (the ASCII subset), and code points outside the ASCII subset were converted to invalid characters, causing the resulting character strings to become invalid. For derived tables without UNION, this led to problems when a column name from the derived table used characters outside the ASCII subset, and was used in the WHERE condition. For derived tables with UNION, it created problems when a character outside the ASCII subset was present in a WHERE condition.

We fix these issues by initializing the string used for representing the condition in such cases to the connection character set. (Bug #109699, Bug #34996488)

问题总结

MySQL 8.0.32 存在UNION语句 中文查不到数据的BUG

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