SELECT NULL in SQL

The NULL value in SQL represents missing or unknown data. You can use NULL in SELECT statements to explicitly select a NULL value, or to check for NULL in conditions.

1. Selecting a NULL literal

You can select a NULL value directly (often for testing or as a placeholder):

SELECT NULL;

Result: Returns one row with NULL value.

You can also select NULL alongside other columns:

SELECT id, name, NULL AS some_columnFROM employees;

Here, some_column will be NULL for every row.

2. Checking for NULL in WHERE

Since NULL means unknown, you cannot use = NULL. Instead, use:

SELECT * FROM employeesWHERE column_name IS NULL;

Or to find non-null values:

SELECT * FROM employeesWHERE column_name IS NOT NULL;

3. Using NULL with functions

You can use functions like COALESCE or IFNULL to replace NULL with a default value:

SELECT name, COALESCE(phone, 'No Phone') AS phone_numberFROM employees;

Summary:

• SELECT NULL returns a null literal.

• Use IS NULL or IS NOT NULL to check for nulls in conditions.

• Use COALESCE to handle null values gracefully.

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