SQL NULL Values: Main Tips
- This value defines lost data.
- Tables already contain NULL values.
- NULL is handled not like other values.
SQL Working with NULL Values
Below there is a table called "People":
Hypothetically the "Adress" column is optional. Then when you write a data record without a value assigned it will receive NULL.
Testing is unavailable using default operators, that's why we use IS NULL/IS NOT NULL.
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IS NULL: Example
To select NULL data records we use IS NULL operator:
SELECT col_names FROM tbl_name WHERE col_name IS NULL;
SELECT Name, Unit FROM Products WHERE Unit_On_Order IS NULL;
IS NOT NULL: Example
To select data records with no NULL values we use IS NOT NULL operator:
SELECT col_names FROM tbl_name WHERE col_name IS NOT NULL;
SELECT Name, Price FROM Products WHERE Unit_On_Order IS NOT NULL;