mysql中union和union or

UNION 和 UNION ALL 是 MySQL 中用于合并多个 SELECT 查询结果的操作符。

UNION 会合并多个 SELECT 查询的结果集，并去除重复的行。它的语法如下：

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

UNION ALL 同样合并多个 SELECT 查询的结果集，但不去除重复的行。它的语法如下：

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

而 "UNION OR" 并不是 MySQL 中的有效操作符。也就是说，在 MySQL 中没有 "UNION OR" 这个语法。或许您对 "UNION OR" 的意图是使用 UNION 和 OR 运算符来进行复杂的查询操作，但这种语法是不支持的。如果您有更具体的需求，可以提供详细信息，我将尽力帮助您解决问题。

相关问题

mysql中or 和union的区别

MySQL中的OR和UNION是两个不同的操作符。

OR是逻辑运算符，用于连接两个或多个条件，只要其中一个条件成立，整个条件就成立。例如：

SELECT * FROM table WHERE column1 = 'value1' OR column2 = 'value2';

这个查询会返回所有满足column1等于'value1'或column2等于'value2'的行。

UNION是用于合并两个或多个SELECT语句的操作符。它会将两个SELECT语句的结果集合并成一个结果集。例如：

SELECT column1 FROM table1
UNION
SELECT column2 FROM table2;

这个查询会返回table1中column1列的所有值和table2中column2列的所有值的并集。

总之，OR是用于连接条件的逻辑运算符，而UNION是用于合并结果集的操作符。

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 using UNION is as follows:

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

The two SELECT statements must have the same number of columns, and the data types of the corresponding columns must be compatible. The resulting columns in the output will have the same name as the corresponding columns in the first SELECT statement.

UNION eliminates duplicate rows from the result set. If you want to include duplicate rows, you can use the UNION ALL operator instead.

Example:

Suppose we have two tables "employees" and "customers" with the following data:

employees table:

| emp_id | emp_name | emp_salary |
|--------|-----------|------------|
| 1 | John | 50000 |
| 2 | Jane | 60000 |
| 3 | Bob | 45000 |

customers table:

| cust_id | cust_name | cust_city |
|--------|-----------|-----------|
| 1 | Mary | New York |
| 2 | Tom | Chicago |
| 3 | Sarah | Boston |

Now, if we want to combine the data from both tables, we can use UNION as follows:

SELECT emp_name, emp_salary FROM employees
UNION
SELECT cust_name, NULL FROM customers;

This will give us the following result set:

| emp_name | emp_salary |
|-----------|------------|
| John | 50000 |
| Jane | 60000 |
| Bob | 45000 |
| Mary | NULL |
| Tom | NULL |
| Sarah | NULL |

Note that we have used NULL in the SELECT statement for the second table to match the number of columns in the first table.