The difference between not equal to null and is not null in oracle

NOT NULL is a column constraint that prohibits the insertion of NULL values; IS NOT NULL is a check operator that evaluates whether the column does not contain NULL values.

The difference between NOT NULL and IS NOT NULL in Oracle

NOT NULL and IS NOT NULL are two related but not identical relational operators in Oracle that are used to specify column constraints.

NOT NULL

NOT NULL The constraint specifies that the column cannot contain NULL values. This means that the column must always contain a non-null value. Oracle will throw an error if you try to insert a NULL value into a column that has a NOT NULL constraint.

IS NOT NULL

On the other hand, the IS NOT NULL operator is used to check if the column does not contain NULL value. It returns a Boolean value: TRUE if the column does not contain NULL values, or FALSE if it does.

Key Differences

The key difference between NOT NULL and IS NOT NULL is:

• Constraints and checks: NOT NULL is a constraint that defines the behavior of a column, while IS NOT NULL is a check operator, used to evaluate the current contents of the column.
• NULL insertion: The NOT NULL constraint prohibits the insertion of NULL values, while the IS NOT NULL operator does not prevent the insertion of NULL values.

Usage

Although both operators are used to ensure that a column contains non-NULL values, they are used in different situations:

• Define column constraints: NOT NULL Constraints are used to define column behavior when creating a table.
• Check column contents: IS NOT NULL operator is used in a query to check whether a column does not contain NULL values.

Example

The following example demonstrates the difference between these two operators:

<code>CREATE TABLE MyTable (
  id NUMBER NOT NULL,
  name VARCHAR2(255)
);

INSERT INTO MyTable (id) VALUES (1); -- OK
INSERT INTO MyTable (name) VALUES (NULL); -- Error

SELECT * FROM MyTable WHERE name IS NOT NULL; -- Returns row with non-NULL name</code>

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