Select Basics

Select COALESCE NULL

If every COALESCE operand is NULL, the expression result is NULL.

highlighted = computed this step

Input table

Use the same contacts with missing email and phone cells.

Contacts\text{Contacts}
Contactscustomer_idemailphonec1email_aNULLc2NULLphone_bc3NULLNULL

Select query

Use COALESCE across only the two contact columns.

COALESCE email, phone\text{COALESCE email, phone}
SELECT COALESCE without defaultselect customer_id,contact_or_nullarity 2 rows 3Contactsarity 3 rows 3

Output table

The row with no contact values stays NULL.

contact or NULL\text{contact or NULL}
Outputcustomer_idcontact_or_nullc1email_ac2phone_bc3NULL