MySQL group_concat to add a separator for empty fields?

For this, you can use replace() along with group_concat(). Here, for empty fields, we are displaying a comma as a separator. Let us first create a table −

mysql> create table DemoTable (    Id int,    Number varchar(100) ); Query OK, 0 rows affected (2.03 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable values(10,'456'); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable values(11,'345'); Query OK, 1 row affected (0.28 sec) mysql> insert into DemoTable values(10,''); Query OK, 1 row affected (0.63 sec) mysql> insert into DemoTable values(10,'278'); Query OK, 1 row affected (0.35 sec) mysql> insert into DemoTable values(10,''); Query OK, 1 row affected (0.37 sec) mysql> insert into DemoTable values(10,'789'); Query OK, 1 row affected (0.47 sec)

Display all records from the table using select statement −

mysql> select *from DemoTable;

This will produce the following output −

+------+--------+ | Id   | Number | +------+--------+ |   10 | 456    | |   11 | 345    | |   10 |        | |   10 | 278    | |   10 |        | |   10 | 789    | +------+--------+ 6 rows in set (0.00 sec)

Following is the query to add a separator for empty fields −

mysql> select Id,replace(group_concat(Number),',,',',') from DemoTable group by Id;

This will produce the following output −

+------+----------------------------------------+ | Id   | replace(group_concat(Number),',,',',') | +------+----------------------------------------+ |   10 | 456,278,789 | |   11 | 345 | +------+----------------------------------------+ 2 rows in set (0.00 sec)