Cách nối chuỗi với SELECT * trong MySQL

Để nối chuỗi trong MySQL, sử dụng hàm CONCAT(). Cú pháp như sau:

SELECT CONCAT(ten_cot1, 'chuoi_noi'), CONCAT(ten_cot2, 'chuoi_noi'), ... FROM ten_bang;

Ví dụ minh họa: tạo bảng selectConcat:

mysql> CREATE TABLE selectConcat (
    -> StudentId INT,
    -> StudentName VARCHAR(100),
    -> StudentAge INT
    -> );

Chèn dữ liệu mẫu:

mysql> INSERT INTO selectConcat VALUES (1, 'Carol', 23);
mysql> INSERT INTO selectConcat VALUES (2, 'John', 24);
mysql> INSERT INTO selectConcat VALUES (3, 'Adam', 25);
mysql> INSERT INTO selectConcat VALUES (4, 'Bob', 21);
mysql> INSERT INTO selectConcat VALUES (5, 'Sam', 22);

Hiển thị dữ liệu gốc:

mysql> SELECT * FROM selectConcat;

+-----------+-------------+------------+
| StudentId | StudentName | StudentAge |
+-----------+-------------+------------+
| 1         | Carol       | 23         |
| 2         | John        | 24         |
| 3         | Adam        | 25         |
| 4         | Bob         | 21         |
| 5         | Sam         | 22         |
+-----------+-------------+------------+

Sử dụng CONCAT() để nối chuỗi:

mysql> SELECT CONCAT(StudentId, ' as an Id'), CONCAT(StudentName, ' as a Name') FROM selectConcat;

Kết quả:

+-------------------------------+----------------------------------+
| CONCAT(StudentId,' as an Id') | CONCAT(StudentName,' as a Name') |
+-------------------------------+----------------------------------+
| 1 as an Id                    | Carol as a Name                  |
| 2 as an Id                    | John as a Name                   |
| 3 as an Id                    | Adam as a Name                   |
| 4 as an Id                    | Bob as a Name                    |
| 5 as an Id                    | Sam as a Name                    |
+-------------------------------+----------------------------------+