在 Mysql 中，我们可以从子查询中返回一个数组吗

Question

In postgres, if we want to retrieve any array of data from a subquery we just use array constructor. Similarly to that in Mysql, is there any way to retrieve an array of data from a subquery?

Example:

• In role we have schema like id, name, description
• In user table we have like id, email
• In user_role table we have schema like id, role_id,user_id

user_role hasMany roles.

I need a result like user_role.id,role.name and role.name should have an array of values.

Please check below example https://mkyong.com/database/convert-subquery-result-to-array/

Answer 1

mysql doesn't have an array type. You can return a comma separated list of role names:

select user.id, group_concat(role.name order by role.name)
from user
join user_role on user_role.user_id=user.id
join role on role.id=user_role.role_id
group by user.id

or a string containing a json array, eg ["role a name","role b name"] :

select user.id, json_arrayagg(role.name order by role.name)
from user ...

Note that group_concat returns a string that will be truncated at @@group_concat_max_len characters, a system variable that defaults to 1024 in mysql.