Simply say coalesce the daily use of the function

Coalesce

The function is to return the first non-null value.

SELECT COALESCE (null,null,'A','CC') -- -- A

The principle is actually equivalent to

Case where A is isn't null then a

When a B is isn't null then B

.

.

.

else N End

Really good for simplifying code ~

--summarize below 3 points--1, can not all constants are used NULL, only the part of the errorSELECT COALESCE(NULL,NULL) --2, for the situation 1, with variable words is possible! DECLARE @A INT = NULL,        @B VARCHAR( -)= NULLSELECT COALESCE(@A,@B)-----------NULL--3, careful data type difference!! Beware of data type differences!! Beware of data type differences!! --Coalesce returns the highest type of data type in each itemSELECT COALESCE(1,'A')--OKSELECT COALESCE('A',1)--ErrorThat's the reason.

Simply say coalesce the daily use of the function