Starting with MariaDB ColumnStore 1.1, the ability to create and use user-defined aggregate and window functions is supported in addition to scalar functions. With Columnstore 1.2, multiple parameters are supported. A C++ SDK is provided, as well as 3 reference examples that provide additional functions that may be of general use:
median—mathematical median, equivalent to percentile_cont(0.5).
avg_mode—mathematical mode, i.e., the most frequent value in the set.
SSQ—sum of squares, i.e., the sum of each number squared in the set.
Similar to built-in functions, the SDK supports distributed aggregate execution, where much of the calculation is scaled out across PrimProc nodes.
The reference examples above are included in the standard build of MariaDB ColumnStore. They can be used by registering them as user-defined aggregate functions. The same can be done for new functions, assuming the instance has the updated libraries included.
From a mcsmysql prompt:
After this, they may be used in the same way as any other aggregate or window function, like SUM:
This requires a MariaDB ColumnStore source tree and the necessary tools to compile C/C++ code. The SDK and reference examples are available in the utils/udfsdk directory of the source tree. It contains the SDK documentation, which is also available here:
The implementation of the median and avg_mode functions will scale in memory consumption to the size of the set of unique values in the aggregation.
CREATE AGGREGATE FUNCTION median RETURNS REAL soname 'libudf_mysql.so';
CREATE AGGREGATE FUNCTION avg_mode RETURNS REAL soname 'libudf_mysql.so';
CREATE AGGREGATE FUNCTION ssq RETURNS REAL soname 'libudf_mysql.so';SELECT grade,
AVG(loan_amnt) AVG,
MEDIAN(loan_amnt) median
FROM loanstats
GROUP BY grade
ORDER BY grade;This page is: Copyright © 2025 MariaDB. All rights reserved.