SQL - IS NULL

The "IS NULL" operator in SQL is used to check if a column has a NULL value. It returns true if the column value is NULL and false if it is not.

A field with a NULL value denotes that it has no value. It is possible to create a new record or update an existing record without providing a value for a field in a table. If we do so, the field will then be saved with the value NULL.

Comparison operators pke =, <, or <> cannot be used to check for NULL values. Instead, we use the following operators.

Is null

Is not null (negation of NULL values)

Null value in SQL

SQL does not permit leaving any field of a column without value. logically, table columns without values are empty fields. In reapty, fields having an unspecified value are regarded as NULL. When we don t enter anything into a table cell, SQL assumes that there is a value that, at this time, is unknown but might one day be known and placed in this field.

Syntax

Following is the syntax for null value −

SELECT column_name1, column_name2, column_name3, ... , column_nameN
FROM table_name
WHERE column_nameN = NULL

The IS NULL Operator

SQL IS NULL is a logical operator that enables you to filter out rows with missing data from your results. Null values, or cells without any data, can appear in some tables. IS NULL allows you to choose rows in a given column that are empty.

Syntax

Following is the syntax for IS NULL −

SELECT column_name1, column_name2, column_name3, ... , column_nameN
FROM table_name
WHERE column_nameN IS NULL

Example

Let’s consider a table named "Fruit" that we are going to create in our database and which contains some null values in the fields. Execute the below query to create a table.

SQL> CREATE TABLE Fruit  
(  
   ID   INT              NOT NULL,
   NAME VARCHAR (20)     NOT NULL,
   ADDRESS  CHAR (25),
   PRICE   DECIMAL (18, 2),       
   PRIMARY KEY (ID)
);

Now we are going to populate the above-created table by using the below query.

SQL> INSERT INTO Fruit (ID,NAME,ADDRESS,PRICE)
VALUES (1,  Apple ,  Shimla , 2000.00 );

INSERT INTO Fruit (ID,NAME,ADDRESS,PRICE)
VALUES (2,  Mango ,NULL, 3000.00 );

INSERT INTO Fruit (ID,NAME,ADDRESS,PRICE)
VALUES (3,  Orange ,NULL, 4000.00 );

INSERT INTO Fruit (ID,NAME,ADDRESS,PRICE)
VALUES (4,  Banana ,  AP ,NULL);

INSERT INTO Fruit (ID,NAME,ADDRESS,PRICE)
VALUES (5,  JackFruit ,  Ooty ,NULL);

Verification

To check whether the table is created or not, let’s execute the below query.

SQL> SELECT * FROM Fruit;

On executing it, it will display a table as shown below −

+----+-----------+---------+---------+
| ID | NAME      | ADDRESS | PRICE   |
+----+-----------+---------+---------+
|  1 | Apple     | Shimla  | 2000.00 |
|  2 | Mango     | NULL    | 3000.00 |
|  3 | Orange    | NULL    | 4000.00 |
|  4 | Banana    | AP      |    NULL |
|  5 | JackFruit | Ooty    |    NULL |
+----+-----------+---------+---------+

IS NULL with SELECT statement

We can use IS NULL operator with a SELECT statement to filter rows based on whether a particular column contains a NULL value or not.

Example

In the following query, we are going to show how the IS NULL condition is going to be used to select rows if the specified field is NULL.

SQL> SELECT *
FROM Fruit
WHERE ADDRESS IS NULL;

Output

On executing the above query, it will generate an output as shown below −

+----+--------+---------+---------+
| ID | NAME   | ADDRESS | PRICE   |
+----+--------+---------+---------+
|  2 | Mango  | NULL    | 3000.00 |
|  3 | Orange | NULL    | 4000.00 |
+----+--------+---------+---------+

IS NULL with COUNT() function

We can also use the IS NULL operator with the COUNT() function in SQL to count the number of rows that contain NULL values in a particular column. This function is utipzed along with the SQL SELECT command.

Syntax

Following is the syntax for COUNT() function −

SELECT COUNT(column_name)
FROM table_name
WHERE condition;

Example

The following query determines the count of rows have a blank field (NULL) in Price column.

SQL> SELECT COUNT(*)
FROM Fruit
WHERE PRICE IS NULL;

Output

On executing the above query, it will generate an output as shown below −

+----------+
| COUNT(*) |
+----------+
|        2 |
+----------+

IS NULL with UPDATE statement

We can use the UPDATE statement with the "IS NULL" operator in SQL to set the value of a column to NULL for all rows that meet a certain condition.

Example

Consider the following table "fruit" in our database and run the following query to see how the update statement is used.

SQL> UPDATE Fruit
SET PRICE= 1000
WHERE PRICE IS NULL;

Verification

To check whether the table has been updated or not, execute the below query.

SQL> SELECT * FROM Fruit;

On executing the above query, it will generate the following output as shown below −

+----+-----------+---------+---------+
| ID | NAME      | ADDRESS | PRICE   |
+----+-----------+---------+---------+
|  1 | Apple     | Shimla  | 2000.00 |
|  2 | Mango     | NULL    | 3000.00 |
|  3 | Orange    | NULL    | 4000.00 |
|  4 | Banana    | AP      | 1000.00 |
|  5 | JackFruit | Ooty    | 1000.00 |
+----+-----------+---------+---------+

SQL IS NULL with DELETE statement

We can also use the DELETE statement with IS NULL operator to delete all rows that contain NULL values in a particular column.

Example

Execute the below query to observe how we are going to use the delete statement with is null.

SQL> DELETE FROM Fruit
WHERE ADDRESS IS NULL;

Verification

Execute the below query to check whether the table has been changed or not.

SQL> SELECT * FROM Fruit;

On executing the above query, it will generate the following output as shown below −

+----+-----------+---------+---------+
| ID | NAME      | ADDRESS | PRICE   |
+----+-----------+---------+---------+
|  1 | Apple     | Shimla  | 2000.00 |
|  4 | Banana    | AP      | 1000.00 |
|  5 | JackFruit | Ooty    | 1000.00 |
+----+-----------+---------+---------+