Performing Row and Column Counting : Count « Select Clause « SQL / MySQL






  1. SQL / MySQL
  2. Select Clause
  3. Count

Performing Row and Column Counting

/*
mysql> SELECT COUNT(*) AS NumberOfExams,
    ->        COUNT(DISTINCT SustainedOn) AS UniqueDates,
    ->        COUNT(Comments) AS ExamsWithComments
    -> FROM Exam;
+---------------+-------------+-------------------+
| NumberOfExams | UniqueDates | ExamsWithComments |
+---------------+-------------+-------------------+
|             3 |           3 |                 3 |
+---------------+-------------+-------------------+
1 row in set (0.00 sec)


*/

/* Create the table */
Drop TABLE Exam;

CREATE TABLE Exam (
   ExamID      INT NOT NULL PRIMARY KEY,
   SustainedOn DATE,
   Comments    VARCHAR(255)
   
)TYPE = InnoDB;

/* Insert data */
INSERT INTO Exam (ExamID,SustainedOn,Comments) VALUES (1,'2003-03-12','Java test');
INSERT INTO Exam (ExamID,SustainedOn,Comments) VALUES (2,'2003-03-13','C# test');
INSERT INTO Exam (ExamID,SustainedOn,Comments) VALUES (3,'2003-03-11','JavaScript test');

/* Real command */  
SELECT COUNT(*) AS NumberOfExams,
       COUNT(DISTINCT SustainedOn) AS UniqueDates,
       COUNT(Comments) AS ExamsWithComments
FROM Exam;








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