Add NULL support in count function

[yupeng9]

To support queries like count(col) where col can have NULL values, or count(CASE WHEN condition THEN v END)

In certain cases, there's no workaround to calculating such values.

[Jackie-Jiang]

Please take a look at the feature proposed by @atris #7519. We can model the query as SELECT COUNT(*) FILTER (WHERE col IS NOT NULL), ...

[yupeng9]

Yes, I left some comments in the doc. At the syntax level, can we make the feature SQL standard compatible?

[Jackie-Jiang]

It is actually standard SQL but as optional feature: https://modern-sql.com/feature/filter

[yupeng9]

Sorry, I meant mainstream query engines like MySQL and Presto.

[atris]

The syntax is the same as supported by mainstream engines (as highlighted by @Jackie-Jiang)