COALESCE function in BigQuery

The COALESCE function in BigQuery is used to return the first non-NULL expression among its arguments. If all expressions evaluate to NULL, the function returns NULL.

SQL Syntax

COALESCE(expression1, expression2, ..., expressionN)    

Key Rules

• Expressions are evaluated from left to right.
• The first non-NULL value is returned.

Example:

SQL

SELECT COALESCE(NULL, "", "Ashish") AS return_value;    

The result of the above query is shown below:

Evaluation Order

• NULL is ignored because it is NULL.
• "" is an empty string, but it is NOT NULL.
• "Ashish" is never reached.

Important Concept

• "" (empty string) is NOT NULL.
• COALESCE() does not skip empty strings.