Feature/202 aql function

[chevalleyc]

Function Support

A number of postgresql functions are now supported. The following list the functions currently supported by EHRbase AQL engine. More functions will likely be added later on.

The functions below essentially deal with scalar values passed as argument, that is passing a canonical json as argument yields unpredictable results (this should be addressed with better error handling later on).

For example, the count function expect a scalar argument (nb. '*' is not supported in this implementation):

{
  "q": "SELECT count(e/ehr_id/value)  FROM EHR e"
}

NB. This is an initial implementation, further tests and enhancements are expected.

Aggregate & Statistical Functions

See https://www.postgresql.org/docs/current/functions-aggregate.html for more details on parameters.

COUNT, AVG, BOOL_AND, BOOL_OR, EVERY, MAX, MIN, SUM

Statistics Functions

correlation

CORR

covariance

COVAR_POP, COVAR_SAMP

regression

REGR_AVGX, REGR_AVGY, REGR_COUNT, REGR_INTERCEPT, REGR_R2, REGR_SLOPE, REGR_SXX, REGR_SXY, REGR_SYY

standard deviation

STDDEV, STDDEV_POP, STDDEV_SAMP, VARIANCE, VAR_POP, VAR_SAM

See https://www.postgresql.org/docs/current/static/functions-aggregate.html for more details

String Functions

SUBSTR, STRPOS, SPLIT_PART, BTRIM, CONCAT, CONCAT_WS, DECODE, ENCODE, FORMAT, INITCAP, LEFT, LENGTH, LPAD LTRIM, REGEXP_MATCH, REGEXP_REPLACE, REGEXP_SPLIT_TO_ARRAY, REGEXP_SPLIT_TO_TABLE, REPEAT, REPLACE, REVERSE RIGHT, RPAD, RTRIM, TRANSLATE

See https://www.postgresql.org/docs/current/static/functions-string.html for more details.

Limitations

Embedded expressions or embedded functions are not yet supported.

Related issue

Closes: https://github.com/ehrbase/project_management/issues/202

Additional information and checks

• Pull request linked in changelog