Initializes aggregation for your input rows. It is intended for the functions with the suffix
Use it for tests or to process columns of types
initializeAggregation (aggregate_function, column_1, column_2)
aggregate_function— Name of the aggregation function. The state of this function — the creating one. String.
column_n— The column to translate it into the function as it's argument. String.
Returns the result of the aggregation for your input rows. The return type will be the same as the return type of function, that
initializeAgregation takes as first argument.
For example for functions with the suffix
State the return type will be
SELECT uniqMerge(state) FROM (SELECT initializeAggregation('uniqState', number % 3) AS state FROM system.numbers LIMIT 10000);
│ 3 │