Count takes NULL or Not

Question

1)Count doesnot take NULL values, but Count(*) returns NULL values. Is it true?

The COUNT function can tell you the total number of rows returned in a result set (both NULL and non-NULL together depending on how it's used). For example: Using SELECT COUNT(*) or SELECT COUNT(1) (which is what I prefer to use) will return the total of all records returned in the result set regardless of NULL values

2)Other than Count what else return NULL values as part of calculation

3)Avg., sum,update these  are not take NULL take in calculation. right?

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there are some contradictory statement here and here

Comments

@shaik yes that i knw airthmetic opns with null result in null only.

Hmm you can say that way too..:)

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@shaik

" UPDATE S set B=10 where B is NULL"

can we update NULL value like this??

Is there any good link where update work with NULL like this??

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mam, no need any special reference, you can try it in database directly...

Answer 1

• Count(*) ----> number of records in the table.

• Count(A) ----> number of non null value over A.

• Sum(A) ----> sum of non null value of attribute A.

• Avg(A) ----> avg of non null value of attribute A.