sql에서 count 널 취급함?

[익명(220.78)]

count(*) 은

모든 컬럼이 null이어도 카운팅하고

count(c1)은 c1컬럼이 null이면 카운팅 안하잖아

문제랑 실험결과가 다름

[익명(lpiecel)]

https://learn.microsoft.com/en-us/sql/t-sql/functions/count-transact-sql?view=sql-server-ver16
조건에
따라 다름

[익명(lpiecel)]

COUNT(*) returns the number of items in a group. This includes NULL values and duplicates. COUNT(ALL expression) evaluates expression for each row in a group, and returns the number of nonnull values. COUNT(DISTINCT expression) evaluates expression for each row in a group, and returns the number of unique, nonnull values.

[익명(220.78)]

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