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SQL IS NULL condition
The IS NULL condition is used in SQL to check the NULL value. It returns TRUE if NULL is found, otherwise it returns FALSE. It can be used in SELECT, INSERT, UPDATE or DELETE.
Syntax for IS NULL condition in SQL
IS NULL expression_id
where:
- expression_id – Expression to check NULL value.
Using IS NULL with SELECT operator
When tested on NULL value, IS NULL is the recommended comparison operator for use in SQL. Let us start with an example which shows how to use the IS NULL condition in a SELECT query.
In this example, we have a table with the following data:
| custom_id | f_name | l_name | fav_website |
|---|---|---|---|
| 4000 | Justin | Bieber | google.com |
| 5000 | Selena | Gomez | bing.com |
| 6000 | Mila | Kunis | yahoo.com |
| 7000 | Tom | Cruise | oracle.com |
| 8000 | Johnny | Depp | NULL |
| 9000 | Russell | Crowe | google.com |
Enter the following SQL statement:
SELECT *
FROM customs
WHERE fav_website IS NULL;
Will be selected 1 entry. Here are the results you will get:
| custom_id | f_name | l_name | fav_website |
|---|---|---|---|
| 8000 | Johnny | Depp | NULL |
In this example we will return all records from the customers table, where fav_website field contains value NULL.
Using IS NULL with UPDATE operator
Next, let’s consider an example of using the IS NULL condition in the UPDATE query.
In this example, we have a product table containing the following data:
| prod_id | prod_name | cat_id |
|---|---|---|
| 1 | Pear | 50 |
| 2 | Banana | 50 |
| 3 | Orange | 50 |
| 4 | Apple | 50 |
| 5 | Bread | 75 |
| 6 | Sliced Ham | 25 |
| 7 | Kleenex | NULL |
Enter the following UPDATE request:
UPDATE prods
SET cat_id = 110
WHERE cat_id IS NULL;
1 record will be updated. Select the data from the products table again:
SELECT *
FROM prods;
here are the results you should get:
| prod_id | prod_name | cat_id |
|---|---|---|
| 1 | Pear | 50 |
| 2 | Banana | 50 |
| 3 | Orange | 50 |
| 4 | Apple | 50 |
| 5 | Bread | 75 |
| 6 | Sliced Ham | 25 |
| 7 | Kleenex | 110 |
In this example, all cat_id values in the products table will be updated to 110, where cat_id contains the NULL value. As you can see, cat_id in the last line has been updated to 110.
Using IS NULL with DELETE operator
Next, let’s consider an example of using the IS NULL condition in the DELETE operator.
In this example, we have a table with the following data:
| ord_id | custom_id | ord_date |
|---|---|---|
| 1 | 7000 | 2019/06/18 |
| 2 | 5000 | 2019/06/18 |
| 3 | 8000 | 2019/06/19 |
| 4 | 4000 | 2019/06/20 |
| 5 | NULL | 2019/07/01 |
Enter the following DELETE operator:
DELETE FROM ords
WHERE custom_id IS NULL;
1 record will be deleted. Select the data from the order table again:
SELECT *
FROM ords;
Here are the results you’ll get:
| ord_id | custom_id | ord_date |
|---|---|---|
| 1 | 7000 | 2019/06/18 |
| 2 | 5000 | 2019/06/18 |
| 3 | 8000 | 2019/06/19 |
| 4 | 4000 | 2019/06/20 |
In this example, all records from the order table, where custom_id contains NULL value, will be deleted. As you can see, the request has deleted the record for ord_id = 5.
How to use the SQL IS NULL Condition
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