How to use Mysql's GROUP_CONCAT() function_PHP tutorial-PHP Tutorial-php.cn

How to use Mysql's GROUP_CONCAT() function_PHP tutorial

WBOY

Release： 2016-07-21 15:53:14

Original

1301 people have browsed it

Syntax:

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

Let’s demonstrate this function. First, create a student course selection table student_courses and fill in some test data.

SQL code

Copy code The code is as follows:

CREATE TABLE student_courses ( 
 student_id INT UNSIGNED NOT NULL, 
 courses_id INT UNSIGNED NOT NULL, 
 KEY(student_id) 
); 
INSERT INTO student_courses VALUES (1, 1), (1, 2), (2, 3), ( 2, 4), (2, 5); 

To find the course selected by student ID 2, use the following SQL:

SQL code

Copy code The code is as follows:

mysql> SELECT student_id, courses_id FROM student_courses WHERE student_id=2; 
+- -----------+----------------+ 
| student_id | courses_id | 
+------------+ ------------+                                                                              
+--------- ---+----------------+ 
3 rows IN SET (0.00 sec) 

 

The output result has 3 records, indicating the student ID Three courses, 3, 4, and 5, were selected for student 2. 

If placed in PHP, a loop must be used to get these 3 records, as shown below:

PHP code

Copy the code

The code is as follows: foreach ($pdo->query("SELECT student_id, courses_id FROM student_courses WHERE student_id=2") as $row) {

$result[] = $row['courses_id'];

} 

If you use the GROUP_CONCAT() function and the GROUP BY statement, it is very simple, as shown below:

SQL code

Copy code

The code is as follows: mysql> SELECT student_id, GROUP_CONCAT( courses_id) AS courses FROM student_courses WHERE student_id=2 GROUP BY student_id; 🎜>+------------+---------+ ----+---------+

1 row IN SET (0.00 sec)

 
This way the processing in php is simple: 

PHP code

Copy code

The code is as follows:

$row = $pdo-> query("SELECT student_id, GROUP_CONCAT(courses_id) AS courses FROM student_courses WHERE student_id=2 GROUP BY student_id");

$result = explode(',', $row['courses']); The

separator can also be customized. The default is "," as the separator. If you want to change it to "|||", use SEPARATOR to specify it, for example:

SQL code

Copy code The code is as follows:

SELECT student_id, GROUP_CONCAT(courses_id SEPARATOR '|||') AS courses FROM student_courses WHERE student_id=2 GROUP BY student_id; 

In addition, you can also sort the values of this group and then concatenate them into strings, for example, sort by courses_id in descending order:

SQL code

Copy code The code is as follows:

SELECT student_id, GROUP_CONCAT(courses_id ORDER BY courses_id DESC) AS courses FROM student_courses WHERE student_id=2 GROUP BY student_id;

Php8, I'm coming too

Learn website layout in 30 minutes

Shangguan Oracle Beginner to Proficient Video Tutorial

Your first line of UNI-APP code

Flutter from scratch to app launch

Brother Lian New Linux Video Tutorial

AXURE 9 Video Tutorial (Suitable for Product Manager Interactive Product Design UI)

Zero Basic Proficiency PS Video Tutorial

16 day UI video tutorial to get you started

PS Techniques and Slicing Techniques Video Tutorial

Alibaba Cloud Environment Construction and Project Launch Video Tutorial

Overview of Computer Networks - Basic Knowledge that Programmers Must Master

Essential Tutorial for Programmers - HTTP Protocol Explanation

Websocket Video Tutorial

How to use Mysql's GROUP_CONCAT() function_PHP tutorial