firebird-support - Help creating expression index

Subject	Help creating expression index
Author	Mr. John
Post date	2019-07-17T15:54:29Z

I want to create a index to improve a query like that:

SELECT * FROM MYTABLE WHERE EXTRACT(YEAR FROM datein)=2019 AND EXTRACT(MONTH FROM datein)=1

I can create this index:

CREATE DESCENDING MYINDEX ON MYTABLE COMPUTED BY (EXTRACT(YEAR FROM datein) || EXTRACT(MONTH FROM datein) )

and change the query:

SELECT * FROM MYTABLE WHERE EXTRACT(YEAR FROM datein)|| EXTRACT(MONTH FROM datein)='20191'

index is used,but don't think this is the solution

thanks for any help