[英]Case for NULL in SQL
我有此代码,但无法正常工作。
当有NULL时,它应该给出''out,并且没有标题,但是没有。
SELECT employee.pin,
CASE gender
WHEN 'M' or (employee.titel IS NULL) THEN CONCAT('Mister ', ' ', ' ', person.fname, ', ' )
WHEN 'W' or (employee.titel IS NULL) THEN CONCAT('Mrs ', ' ', ' ', person.fname, ', ' )
WHEN 'M' THEN CONCAT('Mister ', employee.titel, ' ', person.fname, ', ' )
WHEN 'W' THEN CONCAT('Mrs ', employee.titel, ' ', person.fname, ', ' )
END AS salutation
FROM person,employee
where person.pin=employee.pin
ORDER BY pin
您可以使用CONCAT_WS来跳过空值:
SELECT
employee.pin,
CASE WHEN gender='M' THEN CONCAT_WS(' ', 'Mister', employee.titel, person.fname)
WHEN gender='W' THEN CONCAT_WS(' ', 'Mrs', employee.titel, person.fname)
END AS salutation
FROM
person INNER JOIN employee
ON person.pin=employee.pin
ORDER BY pin
您将不得不使用其他CASE
语法,因为NULL
不等于任何值:
CASE
WHEN gender='M' or (employee.titel IS NULL) THEN CONCAT('Mister ', ' ', ' ', person.fname, ', ' )
WHEN gender='W' or (employee.titel IS NULL) THEN CONCAT('Mrs ', ' ', ' ', person.fname, ', ' )
WHEN gender='M' THEN CONCAT('Mister ', employee.titel, ' ', person.fname, ', ' )
WHEN gender='W' THEN CONCAT('Mrs ', employee.titel, ' ', person.fname, ', ' )
WHEN gender IS NULL THEN ...
END AS salutation
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