What is NULL in SQL?

Question

I am confused what is the NULL value in SQL. NULL I think is empty.

So will it contain any garbage value or an unknown value or as 0 in integer or whitespace characters?

+3

user3346352 Feb 24 '14 at 12:00

5 answers

Rahul Tripathi · Answer 1 · 2014-02-24T12:06:55+0000

In simple worlds, you can say that Null is not a data value, but a marker for an unknown value .

Thus, any mathematical operations performed in NULL will result in NULL. For instance,

10 + NULL = NULL

Similarly, if you perform string concatenation with a string, you get: -

'String ' || NULL || 'Concatenation'   -- Result is NULL

, , Null "" " ": , (0) , , , null , SQL, .

, , , , NULL :

StudentName TestResult
X             78
A             89
B             67
C             NULL

, , C NULL- . ?

, , . , 0 ( 0 , , ) . , ,

UNKNOWN NULL

Raging Bull · Answer 2 · 2014-02-24T12:02:40+0000

NULL . , NULL , .

, . , NULL.

NULL , .

NULL . .

Nagaraj S · Answer 3 · 2014-02-24T12:02:51+0000

, . NULL SQL, Null.

NULL " ", , .

NULL . , NULL , .

10 * NULL          -- Result is NULL

MusicLovingIndianGirl · Answer 4 · 2014-02-24T12:02:53+0000

NULL - , / .

, . , . , NULL.

Fabio · Answer 5 · 2014-02-24T12:02:41+0000

Zero is actually not empty, but is considered the value of the uncle, starting with dumentation

Conceptually, NULL means "missing unknown value", and it is interpreted somewhat differently than other values.

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