SQL 合并具有相同 ID 的行

Question

I have two tables and I need to combine the rows.

As far I have:

$sql = "SELECT A.AID, A.Street, B.FirstName, B.LastName                                     
        FROM A 
        LEFT JOIN B 
        ON A.AID = B.AID;";

Could you help me please to merge those rows, where several people live in the same street?

Answer 1

If you are using MySQL, then you would use GROUP_CONCAT() or a JSON aggregation function. The idea is:

SELECT A.AID, A.Street,
       GROUP_CONCAT(B.FirstName, ' ', B.LastName SEPARATOR ', ') as names                                 
FROM A LEFT JOIN
     B 
     ON A.AID = B.AID
GROUP BY A.AID, A.Street;

In SQL Server you would use string_agg() :

SELECT A.AID, A.Street,
       STRING_AGG(CONCAT(B.FirstName, ' ', B.LastName), ', ') as names                                 
FROM A LEFT JOIN
     B 
     ON A.AID = B.AID
GROUP BY A.AID, A.Street;