How to use GROUP BY to concatenate strings in MySQL?
SqlMysqlStringAggregateConcatenationSql Problem Overview
Basically the question is how to get from this:
foo_id foo_name 1 A 1 B 2 C
to this:
foo_id foo_name 1 A B 2 C
Sql Solutions
Solution 1 - Sql
SELECT id, GROUP_CONCAT(name SEPARATOR ' ') FROM table GROUP BY id;
https://dev.mysql.com/doc/refman/8.0/en/aggregate-functions.html#function_group-concat
From the link above, GROUP_CONCAT: This function returns a string result with the concatenated non-NULL values from a group. It returns NULL if there are no non-NULL values.
Solution 2 - Sql
SELECT id, GROUP_CONCAT( string SEPARATOR ' ') FROM table GROUP BY id
More details here.
From the link above, GROUP_CONCAT: This function returns a string result with the concatenated non-NULL values from a group. It returns NULL if there are no non-NULL values.
Solution 3 - Sql
SELECT id, GROUP_CONCAT(CAST(name as CHAR)) FROM table GROUP BY id
Will give you a comma-delimited string
Solution 4 - Sql
SELECT id, GROUP_CONCAT(name SEPARATOR ' ') FROM table GROUP BY id;
:- In MySQL, you can get the concatenated values of expression combinations . To eliminate duplicate values, use the DISTINCT clause. To sort values in the result, use the ORDER BY clause. To sort in reverse order, add the DESC (descending) keyword to the name of the column you are sorting by in the ORDER BY clause. The default is ascending order; this may be specified explicitly using the ASC keyword. The default separator between values in a group is comma (“,”). To specify a separator explicitly, use SEPARATOR followed by the string literal value that should be inserted between group values. To eliminate the separator altogether, specify SEPARATOR ''.
GROUP_CONCAT([DISTINCT] expr [,expr ...]
[ORDER BY {unsigned_integer | col_name | expr} [ASC | DESC] [,col_name ...]]
[SEPARATOR str_val])
OR
mysql> SELECT student_name,
-> GROUP_CONCAT(DISTINCT test_score
-> ORDER BY test_score DESC SEPARATOR ' ')
-> FROM student
-> GROUP BY student_name;
Solution 5 - Sql
The result is truncated to the maximum length that is given by the group_concat_max_len system variable, which has a default value of 1024 characters, so we first do:
SET group_concat_max_len=100000000;
and then, for example:
SELECT pub_id,GROUP_CONCAT(cate_id SEPARATOR ' ') FROM book_mast GROUP BY pub_id
Solution 6 - Sql
Great answers. I also had a problem with NULLS and managed to solve it by including a COALESCE inside of the GROUP_CONCAT. Example as follows:
SELECT id, GROUP_CONCAT(COALESCE(name,'') SEPARATOR ' ')
FROM table
GROUP BY id;
Hope this helps someone else