mysql union if

在MySQL中，UNION是用来合并两个或多个SELECT语句的结果集的操作符。UNION操作符会去除重复的行，而UNION ALL会保留所有的行。

关于你遇到的问题，Error Code: 1271是因为在UNION操作中使用了不同的字符排序规则（collation）。这意味着你的表中的某些字段的字符集和排序规则不一致，导致了非法混合的错误。

解决这个问题的方法是统一字符集和排序规则，可以通过使用COLLATE子句来指定特定的字符集和排序规则，或者在创建表时设置默认的字符集和排序规则。另外，你还可以使用CONVERT函数来显式地将字段转换为相同的字符集和排序规则。

在你提供的SQL语句中，如果将字符型字段全部去掉，可以正常执行，说明问题很可能是因为字符型字段的字符集和排序规则不一致所导致的。你可以尝试使用COLLATE子句或CONVERT函数来解决这个问题。

相关问题

mysql union

The UNION operator in MySQL is used to combine the results of two or more SELECT statements into a single result set. The syntax for the UNION operator is as follows:

SELECT column1, column2, ... FROM table1
UNION
SELECT column1, column2, ... FROM table2

The result of this query will be a combination of the results of the two SELECT statements. The columns in the result set will be the same as those in the first SELECT statement, with any additional columns from the second SELECT statement added to the end.

Note that the UNION operator automatically removes any duplicate rows from the result set. If you want to include duplicate rows, you can use the UNION ALL operator instead:

SELECT column1, column2, ... FROM table1
UNION ALL
SELECT column1, column2, ... FROM table2

This will include all rows from both tables, even if there are duplicates.

mysql UNION

The UNION operator is used in MySQL to combine the result set of two or more SELECT statements into a single result set. The syntax for using the UNION operator is as follows:

SELECT column1, column2, ... FROM table1
UNION
SELECT column1, column2, ... FROM table2
UNION
SELECT column1, column2, ... FROM table3
...

The SELECT statements within the UNION must have the same number of columns and compatible data types. The result set of the UNION operator will contain only distinct rows, meaning that any duplicate rows will be eliminated.

In addition to the standard UNION operator, MySQL also provides two other variations:

- UNION ALL: This operator works the same as UNION, but it does not eliminate duplicate rows. This can be useful if you want to include all rows from all SELECT statements, including duplicates.
- UNION DISTINCT: This operator is the same as UNION, but it explicitly specifies that the result set should only contain distinct rows. This can be useful if you want to ensure that there are no duplicates in the result set, even if the SELECT statements themselves may contain duplicates.