Specific usage of MySQLGROUP_CONCAT

In the following article, the Han nationality wants to talk about the specific use scheme of MySQLGROUP_CONCAT. In order to describe the specific operation steps of MySQLGROUP_CONCAT in more detail, we also give an example to better explain it, the following describes the specific solution.

 
 

  
  
sql: case when, distinct, group by, group_concat  
 
 

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For more information, we recommend that GROUP_CONCAT accumulate the values of a field based on the specified characters. The default Delimiter is comma, and the length of characters that can be accumulated is 1024 bytes. You can modify these parameters.

1. A simple example

 
 

  
  
select group_concat(f_a) from t_one group by f_b; 
 
 

Query by group by f_ B and accumulate f_a in each group.

2. Modify the default delimiter

 
 

  
  
select group_concat(f_a separator '_') from t_one group by f_b; 
 
 

Separator is a keyword followed by the characters to be separated

3. Sorting

 
 

  
  
select group_concat(f_a order by f_a separator '_') from t_one group by f_b; 
 
 

4. Modify the default character size

1) Add the following in the MySQL configuration file:

Group_concat_max_len = 102400 # maximum length you want

2). You can simply execute the statement and set the scope of the action.

 
 

  
  
SET GLOBAL group_concat_max_len=102400;  
  
  
SET SESSION group_concat_max_len=102400; 
 
 

5. Use with concat

Group_concat by default, a large BLOB Object is returned. You can use concat to return a string. You can also add other data in the returned content.

The above content is the description of MySQLGROUP_CONCAT, and I hope it will help you in this regard.