In SQL, NULL
represents a missing or unknown value.
To check for missing values in SQL, we use IS NULL
expression.
The IS NULL
operator, when used in conjunction with WHERE
, helps us figure out what data is missing.
SELECT column_name(s)
FROM table_name
WHERE column_name IS NULL;
Let’s assume we have a table called Person
with the columns ID
, name
, age
, state
, and gender
.
Now, we want to get the names of all people whose ages are missing from the Person
table.
How do we get this information from our table?
The following code shows how to do this using the IS NULL
operator in SQL.
CREATE TABLE Person (ID int,name varchar(100),age int,gender varchar(10),state varchar(15));-- Insert dataINSERT INTO PersonVALUES (1,'Sharon Peller','16','Female','Kogi');INSERT INTO PersonVALUES (2,'Paul Dons', NULL,'Male','Lagos');INSERT INTO PersonVALUES (3,'Ameera Abedayo','28','Female','Imo');INSERT INTO PersonVALUES (4,'Maria Elijah',NULL,'Female','Lagos');INSERT INTO PersonVALUES (5,'David Hassan',NULL,'Male','Abuja');INSERT INTO PersonVALUES (6,'Niniola Disu','28','Female','Lagos');INSERT INTO PersonVALUES (7,'Praise Dominion','16','Female','Ibadan');INSERT INTO PersonVALUES (8,'Joe Smith','16','Male','Lagos');-- QuerySELECT nameFROM PersonWHERE age IS NULL;
Person
with the columns ID
, name
, age
, gender
, and state
.Person
table.IS NULL
operator with the WHERE
keyword.