Anda baru saja melewatkan GROUP BY
QUERY ANDA DENGAN GROUP BY
SELECT
student.StudentID,
student.`Name`,
COUNT(attendance.AttendanceID) AS Total
FROM
student
LEFT JOIN attendance ON student.StudentID = attendance.StudentID
GROUP BY student.StudentID,student.`Name`;
CONTOH DATA
DROP DATABASE IF EXISTS alishaikh; CREATE DATABASE alishaikh;
USE alishaikh
CREATE TABLE student
(
StudentID CHAR(8) NOT NULL,
Name VARCHAR(40),
PRIMARY KEY (StudentID)
);
INSERT INTO student (StudentID,Name) VALUES
('k1052280','Ali Shaikh'),('k1052287','McKenzie Roth'),
('k1052288','Dacey Sullivan'),('k1052294','Zelda Cantu'),
('k1052295','Kimberly Melton'),('k1052296','Tatianna Cantrell'),
('k1052297','Morgan Thornton'),('k1052298','Allistair Barlow'),
('k1052299','Troy Fulton');
CREATE TABLE attendance
(
AttendanceID INT NOT NULL AUTO_INCREMENT,
StudentID CHAR(8) NOT NULL,
PRIMARY KEY (AttendanceID),
KEY (StudentID)
);
INSERT INTO attendance (StudentID) VALUES
('k1052280'),('k1052280'),('k1052287'),('k1052287'),
('k1052288'),('k1052295'),('k1052295'),('k1052295');
DATA SAMPEL DIMUAT
mysql> DROP DATABASE IF EXISTS alishaikh; CREATE DATABASE alishaikh;
Query OK, 2 rows affected (0.01 sec)
Query OK, 1 row affected (0.00 sec)
mysql> USE alishaikh
Database changed
mysql> CREATE TABLE student
-> (
-> StudentID CHAR(8) NOT NULL,
-> Name VARCHAR(40),
-> PRIMARY KEY (StudentID)
-> );
Query OK, 0 rows affected (0.03 sec)
mysql> INSERT INTO student (StudentID,Name) VALUES
-> ('k1052280','Ali Shaikh'),('k1052287','McKenzie Roth'),
-> ('k1052288','Dacey Sullivan'),('k1052294','Zelda Cantu'),
-> ('k1052295','Kimberly Melton'),('k1052296','Tatianna Cantrell'),
-> ('k1052297','Morgan Thornton'),('k1052298','Allistair Barlow'),
-> ('k1052299','Troy Fulton');
Query OK, 9 rows affected (0.00 sec)
Records: 9 Duplicates: 0 Warnings: 0
mysql> CREATE TABLE attendance
-> (
-> AttendanceID INT NOT NULL AUTO_INCREMENT,
-> StudentID CHAR(8) NOT NULL,
-> PRIMARY KEY (AttendanceID),
-> KEY (StudentID)
-> );
Query OK, 0 rows affected (0.02 sec)
mysql> INSERT INTO attendance (StudentID) VALUES
-> ('k1052280'),('k1052280'),('k1052287'),('k1052287'),
-> ('k1052288'),('k1052295'),('k1052295'),('k1052295');
Query OK, 8 rows affected (0.00 sec)
Records: 8 Duplicates: 0 Warnings: 0
QUERY ANDA DENGAN GROUP BY EXECUTED
mysql> SELECT
-> student.StudentID,
-> student.`Name`,
-> COUNT(attendance.AttendanceID) AS Total
-> FROM
-> student
-> LEFT JOIN attendance ON student.StudentID = attendance.StudentID
-> GROUP BY student.StudentID,student.`Name`;
+-----------+-------------------+-------+
| StudentID | Name | Total |
+-----------+-------------------+-------+
| k1052280 | Ali Shaikh | 2 |
| k1052287 | McKenzie Roth | 2 |
| k1052288 | Dacey Sullivan | 1 |
| k1052294 | Zelda Cantu | 0 |
| k1052295 | Kimberly Melton | 3 |
| k1052296 | Tatianna Cantrell | 0 |
| k1052297 | Morgan Thornton | 0 |
| k1052298 | Allistair Barlow | 0 |
| k1052299 | Troy Fulton | 0 |
+-----------+-------------------+-------+
9 rows in set (0.00 sec)
mysql>
COBALAH !!!
order by Total
setelah grup olehGROUP BY
tetapkan default untukORDER BY
. Terkadang tidak. Jadi,ORDER BY
bisa juga digunakan !!!TestResult
dengan kolom(StudentID, Result)
. Saya juga ingin bergabungTestResult
dan akhirnya mendapatkanCOUNT(TestResult.Result)
untuk setiap siswa. Untuk beberapa alasan, saya mendapatkan nilai berlebih untuk COUNT, saat menggunakan subqueries mengembalikan COUNT yang benar.DISTINCT
kata kunci. Apa yang akan menjadi alasan COUNT untuk mengembalikan sesuatu yang berbeda (biasanya lebih tinggi, dan tentu saja, salah) daripada pola subquery?