CODEWITHSUNDEEP
sqlnull
user3346352
user3346352

Reputation: 49

What is NULL in SQL?

I am confuse about what is the value of NULL in SQL. NULL I think is empty.

So will it contain any garbage value or unknown value or like 0 in integer or blank in character?

Upvotes: 3

Views: 3163

Answers (5)

Rahul Tripathi
Rahul Tripathi

Reputation: 172398

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

So any mathematical operations performed on NULL will result in NULL. For example,

10 + NULL = NULL

Similarly if you do string concatenation with string you get:-

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

So you can say that Null means either "not applicable" or "don't know": it is not the same as zero (0) or any other default value, but more importantly, null is treated quite differently from other values in SQL, because it literally has no value.

An example to explain what it means when we say that NULL means UNKNOWN VALUE:

StudentName TestResult
X             78
A             89
B             67
C             NULL

So you can see that the student C got NULL marks in the test. So what does that mean?

Now one can say that the student does not sit in the test or it may be that the student's data is not avaialable. But it definitely does not mean that the student got 0(as if you assign 0 to the student then it would mean that the student appeared in the test and got zero) marks in the test. All we can say that the data for the student is

UNKNOWN or NULL

Upvotes: 3

Nagaraj S
Nagaraj S

Reputation: 13474

It is to indicate that a data value does not exist in the database.NULL is also an SQL reserved keyword used to identify the Null special marker.

NULL means “a missing unknown value” and it is treated somewhat differently from other values.

A field with a NULL value is a field with no value. It is very important to understand that a NULL value is different than a zero value or a field that contains spaces.

10 * NULL          -- Result is NULL

Null (SQL)

SQL NULL

Working with NULL Values

Upvotes: 2

MusicLovingIndianGirl
MusicLovingIndianGirl

Reputation: 5947

NULL is a keyword used to represent unknown/missing data.

Say you have an optional column in your table. You can insert a new record or update an existing record without adding a value to this column. This means that the field will be saved with a NULL value.

Check this for more details.

Upvotes: 2

Fabio
Fabio

Reputation: 23480

Null is not empty actually but it is considered as uknown value, from dumentation

Conceptually, NULL means “a missing unknown value” and it is treated somewhat differently from other values.

You can ready more here

Upvotes: 1

Raging Bull
Raging Bull

Reputation: 18737

A field with a NULL value is a field with no value. It is very important to understand that a NULL value is different than a zero value or a field that contains spaces.

If a column in a table is optional, we can insert a new record or update an existing record without adding a value to this column. This means that the field will be saved with a NULL value.

NULL values are treated differently from other values.

NULL is used as a placeholder for unknown or inapplicable values. Read more about this here.

Upvotes: 2

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