How to correctly connect a MySQL string to a function

The following articles mainly introduce the specific operation scheme of MySQL string connection functions. We will take the concat function in MySQL database as an example to describe in detail, the following describes the specific operations of MySQL string connection functions.

Usage:

CONCAT (str1, str2 ,...)

The MySQL string generated by the connection parameter is returned. If any parameter is NULL, the return value is NULL.

Note:

If all parameters are non-binary strings, the result is a non-binary string.

If the independent variable contains any binary string, the result is a binary string.

A numeric parameter is converted to an equivalent binary string format. To avoid this, you can use an explicit cast type, for example:

Select concat (CAST (int_col as char), char_col)

The concat function of MySQL can connect one or more MySQL strings, such

 
 

  
  
MySQL> select concat('10');  
  
  
+--------------+  
  
  
| concat('10') |  
  
  
+--------------+  
  
  
| 10 |  
  
  
+--------------+  
  
  
1 row in set (0.00 sec)  
  
  
MySQL> select concat('11','22','33');  
  
  
+------------------------+  
  
  
| concat('11','22','33') |  
  
  
+------------------------+  
  
  
| 112233 |  
  
  
+------------------------+  
  
  
1 row in set (0.00 sec)  
 
 

When the MySQL concat function connects to the MySQL string, if one of them is NULL, NULL is returned.

 
 

  
  
MySQL> select concat('11','22',null);  
  
  
+------------------------+  
  
  
| concat('11','22',null) |  
  
  
+------------------------+  
  
  
| NULL |  
  
  
+------------------------+  
  
  
1 row in set (0.00 sec) 
 
 

Concat_ws function in MySQL

Usage:

CONCAT_WS (separator, str1, str2 ,...)

CONCAT_WS () represents CONCAT With Separator, which is a special form of CONCAT. The first parameter is the delimiter of other parameters. The separator is placed between the two MySQL strings to be connected. The delimiter can be a string or another parameter.

Note:

If the Delimiter is NULL, the result is NULL. The function ignores the NULL value after any separator parameter.

For example, separate the strings with commas (,).

 
 

  
  
MySQL> select concat_ws(',','11','22','33');  
  
  
+-------------------------------+  
  
  
| concat_ws(',','11','22','33') |  
  
  
+-------------------------------+  
  
  
| 11,22,33 |  
  
  
+-------------------------------+  
  
  
1 row in set (0.00 sec)  
 
 

Unlike the concat function in MySQL, The concat_ws function does not return NULL because of the NULL value during execution.

 
 

  
  
MySQL> select concat_ws(',','11','22',NULL);  
  
  
+-------------------------------+  
  
  
| concat_ws(',','11','22',NULL) |  
  
  
+-------------------------------+  
  
  
| 11,22 |  
  
  
+-------------------------------+  
  
  
1 row in set (0.00 sec) 
 
 

Group_concat function in MySQL

The complete syntax is as follows:

Group_concat ([DISTINCT] field to be connected [Order by asc/DESC sorting field] [Separator 'delimiter'])

Basic Query

 
 

  
  
MySQL> select * from aa;  
  
  
+------+------+  
  
  
| id| name |  
  
  
+------+------+  
  
  
|1 | 10|  
  
  
|1 | 20|  
  
  
|1 | 20|  
  
  
|2 | 20|  
  
  
|3 | 200 |  
  
  
|3 | 500 |  
  
  
+------+------+  
  
  
6 rows in set (0.00 sec) 
 
 

Group by id and print the value of the name field in one row, separated by commas (, default)

 
 

  
  
MySQL> select id,group_concat(name) from aa group by id;  
  
  
+------+--------------------+  
  
  
| id| group_concat(name) |  
  
  
+------+--------------------+  
  
  
|1 | 10,20,20|  
  
  
|2 | 20 |  
  
  
|3 | 200,500|  
  
  
+------+--------------------+  
  
  
3 rows in set (0.00 sec) 
 
 

Group by id, print the value of name field in one row, separated by semicolons

 
 

  
  
MySQL> select id,group_concat(name separator ';') from aa group by id;  
  
  
+------+----------------------------------+  
  
  
| id| group_concat(name separator ';') |  
  
  
+------+----------------------------------+  
  
  
|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 redundant name field in one row. The above content is an introduction to the specific operation solution of the MySQL string connection function. I hope you will gain some benefits.