SQL:仅当该列值为null时，如何才能更新该列上的值? [英] SQL: How can I update a value on a column only if that value is null?

问题描述

我有一个SQL问题，对于某些人来说可能是基本问题，但使我感到困惑.

I have an SQL question which may be basic to some but is confusing me.

这是表"Person"的列名的示例: PersonalID，FirstName，LastName，Car，HairColour，FavDrink，FavFood

Here is an example of column names for a table 'Person': PersonalID, FirstName, LastName, Car, HairColour, FavDrink, FavFood

假设我输入了该行:

121312，Rayna，Pieterson，BMW123d，Brown，NULL，NULL

121312, Rayna, Pieterson, BMW123d, Brown, NULL, NULL

现在，我要更新此人的值，但仅当新值不为null时，才更新:

Now I want to update the values for this person, but only if the new value is not null, Update:

121312，Rayna，Pieterson，NULL，金发，芬达，NULL

121312, Rayna, Pieterson, NULL, Blonde, Fanta, NULL

新行必须为:

121312，Rayna，Pieterson，BMW123d，Blonde，Fanta，NULL

121312, Rayna, Pieterson, BMW123d, Blonde, Fanta, NULL

所以我在想一些类似的事情:

So I was thinking something along the lines of:

更新人员(个人ID，名字，姓氏，汽车，HairColour， FavDrink，FavFood)设置Car = @Car(其中@Car不为null)，HairColour = @HairColour(其中@HairColour ...)...等.

Update Person(PersonalID, FirstName, LastName, Car, HairColour, FavDrink, FavFood) set Car = @Car (where @Car is not null), HairColour = @HairColour (where @HairColour...)... etc.

我唯一关心的是，我无法在查询末尾对所有条件进行分组，因为它将要求所有值具有相同的条件.如果@HairColour不为空，我是否可以做类似Update HairColour的操作

My only concern is that I can't group all the conditions at the end of the query because it will require all the values to have the same condition. Can't i do something like Update HairColour if @HairColour is not Null

推荐答案

Id为此请使用合并: http://msdn.microsoft.com/en-us/library/ms190349.aspx

Id use coalesce for this: http://msdn.microsoft.com/en-us/library/ms190349.aspx

update Person
set Car = coalesce(@Car, Car), HairColour = coalesce(@HairColour, HairColour)

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