MySQL common function group_concat

Detailed explanation of group_concat function of mysql

group_concat( [DISTINCT] Field to be connected [Order BY sort field ASC/DESC] [Separator 'Separator'])

The following example illustrates:

select * from goods; 

+------+-- ----+
| id| price|
+------+------+
|1 | 10|
|1 | 20|
|1 | 20|
|2 | 20|
|3 | 200 |
|3 | 500 |
+------+------+
6 rows in set (0.00 sec)

Group by id, print the value of the price field in the same row, separated by commas (default)

select id , group_concat(price) from goods group by id; 

+------+--------------------------------+
| id| group_concat(price) |
+- -----+--------------------------------+
|1 | 10,20,20|
|2 | 20 |
|3 | 200,500|
+------+--------------------------------+
3 rows in set (0.00 sec)

group by id and print the value of the price field on one line , semicolon separated

select id,group_concat(price separator ';') from goods group by id; 
+------+--------------------------------- -------------+
| id| group_concat(price separator ';') |
+------+---------------- ------------------+
|1 | 10;20;20 |
|2 | 20|
|3 | 200;500 |
+------+-- --------------------------------+
3 rows in set (0.00 sec)

are grouped by id to remove duplicate redundancy The value of the price field is printed on one line, comma separated
select id,group_concat(distinct price) from goods group by id; 

+------+----------------- ------------+
| id| group_concat(distinct price) |
+------+-------------------- ---------+
|1 | 10,20|
|2 | 20 |
|3 | 200,500 |
+------+-----------------------------+
3 rows in set (0.00 sec)

以id分组，把price字段的值打印在一行，逗号分隔，按照price倒序排列
select id,group_concat(price order by price desc) from goods group by id; 

+------+---------------------------------------+
| id| group_concat(price order by price desc) |
+------+---------------------------------------+
|1 | 20,20,10 |
|2 | 20|
|3 | 500,200|
+------+---------------------------------------+
3 rows in set (0.00 sec)