How to use alternative column value instead of null in BigQuery

How can I use another value when selected column value was NULL in BigQuery?

BigQuery(BQ) is very useful for data analysis or processing.

It is good at handling huge data. It returns summary result in short time.

But data is not always clean.

Sometimes it contains NULL in specific column.

In that case we should use another value.

Then how can we use alternative value ?

So today I introduce about "How to use alternative column value instead of null in BigQuery".