count_if aggregate function
Applies to: 
Databricks SQL Databricks Runtime
Returns the number of true values for the group in expr.
Syntax
count_if ( [ALL | DISTINCT] expr ) [ FILTER ( WHERE cond ) ]
This function can also be invoked as a window function using the OVER clause.
Arguments
expr: A BOOLEAN expression.cond: An optional boolean expression filtering the rows used for aggregation.
Returns
A BIGINT.
count_if(expr) FILTER(WHERE cond) is equivalent to count_if(expr AND cond).
If DISTINCT is specified only unique rows are counted.
Examples
> SELECT count_if(col % 2 = 0) FROM VALUES (NULL), (0), (1), (2), (2), (3) AS tab(col);
3
> SELECT count_if(DISTINCT col % 2 = 0) FROM VALUES (NULL), (0), (1), (2), (2), (3) AS tab(col);
2
> SELECT count_if(col IS NULL) FROM VALUES (NULL), (0), (1), (2), (3) AS tab(col);
1