aggregate_* session settings

These settings are available in system.settings and are autogenerated from source.

aggregate_function_input_format

Format for AggregateFunction input during INSERT operations.

Possible values:

• state — Binary string with the serialized state (the default). This is the default behavior where AggregateFunction values are expected as binary data.
• value — The format expects a single value of the argument of the aggregate function, or in the case of multiple arguments, a tuple of them. They will be deserialized using the corresponding IDataType or DataTypeTuple and then aggregated to form the state.
• array — The format expects an Array of values, as described in the value option above. All elements of the array will be aggregated to form the state.

Examples

For a table with structure:

CREATE TABLE example (
    user_id UInt64,
    avg_session_length AggregateFunction(avg, UInt32)
);

With aggregate_function_input_format = 'value':

INSERT INTO example FORMAT CSV
123,456

With aggregate_function_input_format = 'array':

INSERT INTO example FORMAT CSV
123,"[456,789,101]"

Note: The value and array formats are slower than the default state format as they require creating and aggregating values during insertion.

aggregate_functions_null_for_empty

Enables or disables rewriting all aggregate functions in a query, adding -OrNull suffix to them. Enable it for SQL standard compatibility. It is implemented via query rewrite (similar to count_distinct_implementation setting) to get consistent results for distributed queries.

Possible values:

• 0 — Disabled.
• 1 — Enabled.

Example

Consider the following query with aggregate functions:

SELECT SUM(-1), MAX(0) FROM system.one WHERE 0;

With aggregate_functions_null_for_empty = 0 it would produce:

┌─SUM(-1)─┬─MAX(0)─┐
│       0 │      0 │
└─────────┴────────┘

With aggregate_functions_null_for_empty = 1 the result would be:

┌─SUMOrNull(-1)─┬─MAXOrNull(0)─┐
│          NULL │         NULL │
└───────────────┴──────────────┘