Pernyataan KASUS SQL

Pernyataan SQL CASE sangat kuat dan serbaguna. Ini dapat digunakan dalam pernyataan SELECT, UPDATE dan INSERT. Bahkan dapat digunakan dalam klausa ORDER BY dan GROUP BY. Mari kita periksa satu per satu.

Sintaks

Pertama periksa sintaks dari pernyataan CASE:

CASE
WHEN condition1 THEN result1
WHEN condition2 THEN result2

...
WHEN conditionN THEN resultN
ELSE result
END;

Persiapan Data

Pertama pilih database pilihan Anda dan jalankan kueri di bawah ini untuk membuat tabel "Orang" dan mengisi dengan data.

IF OBJECT_ID('Persons', 'U') IS NOT NULL
DROP TABLE Persons;
GO

CREATE TABLE Persons(
name varchar(20)
,age int
,sex varchar(2)
)

GO

INSERT INTO Persons (name,age,sex) values('Bob',5, 'M');
INSERT INTO Persons (name,age,sex) values('Harry',15, 'M');
INSERT INTO Persons (name,age,sex) values('Jasmine',25, 'F');
INSERT INTO Persons (name,age,sex) values('Fanny',65, 'F');
INSERT INTO Persons (name,age,sex) values('Evan',-1, 'N');

GO

PILIH Pernyataan

Mari kita gunakan dalam pernyataan SELECT.

SELECT Name, age as 'Actual Age',
CASE
WHEN age >= 0 AND age <= 12 THEN 'CHILD'
WHEN age >= 13 AND age <= 19 THEN 'TEEN AGE'
WHEN age >= 20 AND age <= 40 THEN 'YOUNG'
WHEN age >= 41 AND age <= 60 THEN 'MIDDLE AGE'
WHEN age >= 61 THEN 'OLD'
ELSE 'NOT DEFINED' END as 'New Age using CASE Stmt',
sex as 'Actual Gender',
CASE
WHEN sex = 'M' THEN 'MALE'
WHEN sex = 'F' THEN 'FEMALE'
WHEN sex = 'N' THEN 'DONT WANT TO DISCLOSE'
END as  'New Gender  using CASE Stmt'
FROM Persons

Keluaran

MASUKKAN Pernyataan

DECLARE @age INT
DECLARE @sex VARCHAR(10)

SET @age = 40
SET @sex = 'MALE'
INSERT INTO Persons (Name, Age, Sex)
VALUES(
'Jack',
CASE WHEN @age < 0 THEN -1 ELSE @age END,
CASE WHEN @sex = 'MALE' THEN 'M'
WHEN @sex = 'FEMALE' THEN 'F'
ELSE 'N' END
)

Keluaran

Jika kita menjalankan pernyataan SELECT pertama kita lagi, maka outputnya adalah:

PERBARUI Pernyataan

DECLARE @age INT
SET @age = -4

UPDATE Persons SET
age = CASE WHEN @age < 0 THEN -1 ELSE @age END
WHERE Name = 'Bob'

Keluaran

Jika kita menjalankan pernyataan SELECT di atas lagi, maka outputnya adalah:

ORDER DENGAN Klausul

CASE can be added in ORDER BY clause in above SELECT statement
SELECT Name, age as 'Actual Age',
CASE
WHEN age >= 0 AND age <= 12 THEN 'CHILD'
WHEN age >= 13 AND age <= 19 THEN 'TEEN AGE'
WHEN age >= 20 AND age <= 40 THEN 'YOUNG'
WHEN age >= 41 AND age <= 60 THEN 'MIDDLE AGE'
WHEN age >= 61 THEN 'OLD'
ELSE 'NOT DEFINED' END as 'New Age using CASE Stmt',
sex as 'Actual Gender',
CASE
WHEN sex = 'M' THEN 'MALE'
WHEN sex = 'F' THEN 'FEMALE'
WHEN sex = 'N' THEN 'DONT WANT TO DISCLOSE'
END as  'New Gender  using CASE Stmt'
FROM Persons
ORDER BY
CASE WHEN sex='M' THEN age END,
CASE WHEN sex='F' THEN Name END

Keluaran

GROUP BY Clause

Sekarang saatnya menjelajahi CASE dalam klausa GROUP BY dalam pernyataan SELECT pertama kami:

SELECT
CASE
WHEN age <= 40 THEN 'YOUNG'
WHEN age >= 41 THEN 'OLD'
END as 'New Age using CASE Stmt', COUNT(*)
FROM Persons
GROUP BY CASE
WHEN age <= 40 THEN 'YOUNG'
WHEN age >= 41 THEN 'OLD'
END

Keluaran

Kami membahas semua kasus topik KASUS hari ini.

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