group_concat(column_name

group_concat(column_name)函数用于将指定列的值连接成一个字符串，并可以通过指定分隔符来分隔每个值。下面是两个示例：

1. 使用逗号作为分隔符：

SELECT id, GROUP_CONCAT(name ORDER BY name DESC SEPARATOR ',') 
FROM aa 
GROUP BY id;

输出：

+------+--+
| id   | GROUP_CONCAT(name)          |
+------+--+
| 1    | 20,20,10                    |
| 2    | 20                          |
| 3    | 500,200                     |
+------+--+

2. 使用分号作为分隔符：

SELECT id, GROUP_CONCAT(name SEPARATOR ';') 
FROM aa 
GROUP BY id;

输出：

+------+--+
| id   | GROUP_CONCAT(name)          |
+------+--+
| 1    | 10;20;20                    |
| 2    | 20                          |
| 3    | 200;500                     |
+------+--+

相关问题

group_concat(table_name)

This is a MySQL function that concatenates into a single string all the values in a specified column of a table, separated by a delimiter. The GROUP_CONCAT function is often used with the GROUP BY clause to group the concatenated strings by a particular column.

For example, the following query would concatenate all the values in the "name" column of the "users" table, separated by a comma:

SELECT GROUP_CONCAT(name SEPARATOR ',') FROM users;

The result would be a single string containing all the names in the "users" table, separated by commas.

group_concat

GROUP_CONCAT is a MySQL function that concatenates rows into a single string. It is often used in conjunction with the GROUP BY clause to group multiple rows into a single string value. The syntax for the GROUP_CONCAT function is as follows:

GROUP_CONCAT([DISTINCT] expr [,expr ...]
             [ORDER BY {unsigned_integer | col_name | expr}
                 [ASC | DESC] [,col_name ...]]
             [SEPARATOR str_val])

The DISTINCT keyword is optional and allows for the removal of duplicate values. The expr parameter specifies the column or expression to concatenate. The ORDER BY clause is also optional and allows for the sorting of the concatenated values. The SEPARATOR parameter specifies the delimiter to use between the concatenated values.

Example:

Suppose we have a table called `employees` with the following data:

id   name     department
1    John     Sales
2    Jane     Marketing
3    Bob      Sales
4    Sue      Marketing

If we want to concatenate all the names of employees in each department, we can use the following query:

SELECT department, GROUP_CONCAT(name SEPARATOR ', ') 
FROM employees 
GROUP BY department;

The output would be:

department  GROUP_CONCAT(name SEPARATOR ', ')
Marketing   Jane, Sue
Sales       John, Bob

Note that the values in the GROUP_CONCAT column are separated by a comma and a space (', ').