Скачать или смотреть Using SQL NULLIF with Missing Values | Essential SQL

The NULLIF is a nice short hand way to compare for missing values within columns contains both NULL and blank values.
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Here are the example I used in the video, use them to learn more about NULL IF and play around with it's features:

SELECT FirstNAme, MiddleName, LastName
FROM Person.Person
WHERE NULLIF(MiddleName,'') IS NULL



SELECT FirstNAme, MiddleName, LastName
FROM Person.Person
WHERE case when MiddleName = '' then NULL else MiddleName end IS NULL



SELECT FirstNAme, MiddleName, LastName
FROM Person.Person
WHERE IIF(MiddleName = '',NULL,MiddleName) IS NULL