How to use the GROUP_CONCAT function in MySQL to combine multiple rows of data into a string

How to use the GROUP_CONCAT function in MySQL to merge multiple rows of data into a string

In the MySQL database, sometimes we need to merge multiple rows of data into a string. This situation often occurs when multiple values ​​of a column need to be combined into a single string and separated by commas or other delimiters. MySQL provides a very useful function GROUP_CONCAT to meet this need.

The syntax of 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])

Among them, DISTINCT is optional and is used for deduplication; expr is the column name or expression that needs to be merged; the ORDER BY clause is optional , used to specify the sorting of the merged results; SEPARATOR is optional, used to specify the separator, the default is comma.

The following is an example to demonstrate how to use the GROUP_CONCAT function.

Suppose we have a table fruit, containing two fields: id and name. Among them, the name column contains multiple rows of data. We want to merge the names with the same ID into a string and separate them with commas. The structure and data of the table are as follows:

CREATE TABLE fruit (
    id INT,
    name VARCHAR(50)
);

INSERT INTO fruit (id, name) VALUES (1, '苹果');
INSERT INTO fruit (id, name) VALUES (1, '梨子');
INSERT INTO fruit (id, name) VALUES (1, '香蕉');
INSERT INTO fruit (id, name) VALUES (2, '葡萄');
INSERT INTO fruit (id, name) VALUES (2, '桃子');
INSERT INTO fruit (id, name) VALUES (3, '橙子');

We can use the following SQL statement to merge names with the same ID into a string:

SELECT id, GROUP_CONCAT(name SEPARATOR ',') AS merged_names
FROM fruit
GROUP BY id;

After running the above SQL statement, we can get the following results :

id | merged_names
---|-------------
1  | 苹果,梨子,香蕉
2  | 葡萄,桃子
3  | 橙子

In this example, we grouped based on the id column and used the GROUP_CONCAT function to combine the name column in each grouping into a single string, separated by commas.

It should be noted that if we do not need to remove duplicates, we can omit the DISTINCT keyword. In addition, if you need to sort the merged strings, you can use the ORDER BY clause. For example, we can sort the merged strings in alphabetical order of the name column:

SELECT id, GROUP_CONCAT(name ORDER BY name ASC SEPARATOR ',') AS merged_names
FROM fruit
GROUP BY id;

After running the above SQL statement, we can get the following results:

id | merged_names
---|-------------
1  | 梨子,苹果,香蕉
2  | 桃子,葡萄
3  | 橙子

As you can see, the merge The resulting strings are sorted alphabetically in the name column.

In practical applications, the GROUP_CONCAT function is very practical. By merging multiple rows of data into one string, we can easily summarize and display data and improve the flexibility of database queries.

To summarize, this article introduces the method of using the GROUP_CONCAT function to merge multiple rows of data into a string in MySQL. Through practical example demonstration, I hope readers can master the use of this function and better handle the data merging needs in the database.

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