SUBSTRING_INDEX in HANA - mysql

Question

I'm migrating the database engine an application from MySql to SAP HANA.
I found a little trouble. I have a query like this:
Select SUBSTRING_INDEX(id, "-", -2) as prod_ref From products;
I don't know how to "translate" the function substring_index, because the initial part of the id has a variable length.
Thanks.

Answer 1

This can be done using a regex:
select substr_regexpr( '.*-([^-]*-[^-]*)$' in 'varia-ble---part-part1-part2' group 1) from dummy;
select substr_regexpr( '.*-([^-]*-[^-]*)$' in 'variable-part-part1-part2' group 1) from dummy;
According to the HANA 2.0 SP0 doc you could use locate with a negative offset (and then using right()), but this does not work on my system ("...feature isn't supported...")
If you execute such queries on a regular basis on lots of records I would recommend extracting the part you are interested in during ETL into a separate field. Or, alternatively fill a separate field using " GENERATED ALWAYS AS...".
I have seen it more than once, that people calculate a field like this in complex SQL queries or complex CalcViews, and then wonder why performance is bad when selecting 100 million records and filtering on the calculated field etc... Performance is usually no problem when you have aggregated your intermediate result set to a reasonable size and then apply "expensive" functions.

Answer 2

I don't think there is any direct function like SUBSTRING_INDEX in SAP HANA. But you have a work around alternative by creating a function to pass the input string and delimiter.
And I am assuming that -2 in SUBSTRING_INDEX and providing the solution
Reverse the string and get the position of the second delimiter, '-' in your case, into "obtainedPosition"
Now subtract that "obtainedPosition" from the length of the string.
obtainedPosition = LENGTH(id) - obtainedPosition
Using that value in the inbuilt substring function you can get the required string and return it from the function.
SELECT SCHEMA.FN_SUBSTRING_INDEX(id,obtainedPosition) INTO ReturnValue FROM DUMMY;
CREATE FUNCTION FN_SUBSTRING_INDEX
(
id VARCHAR(500),
delim VARCHAR(2)
)
RETURNS SplitString VARCHAR(500)
LANGUAGE SQLSCRIPT AS
BEGIN
DECLARE reversedString VARCHAR(500);
DECLARE charString VARCHAR(2);
DECLARE i INT := LENGTH(:id);
DECLARE len INT := LENGTH(:id);
DECLARE obtainedPosition INT := 0;
DECLARE flag INT := 0;
reversedString := '';
--loop to reverse the inputstring
WHILE :i > 0
DO
reversedString = CONCAT(:reversedString, SUBSTRING(:id,:i,1));
i := :i - 1;
END WHILE;
--loop to get the second delimiter position
i := 1;
WHILE :i <= :leng
DO
charString := '';
charString := SUBSTRING(:reversedString,i,1);
IF((:charString = :delim ) AND (:flag < 2)) THEN
BEGIN
obtainedPosition := :i;
flag := :flag + 1;
END;
END IF;
i := :i + 1;
END WHILE;
--IF condition to check if at least 2 delimiters are available, else print complete string
IF(flag = 2) THEN
obtainedPosition := :len - :obtainedPosition + 2; --2 is added to avoid the character at that position and '-' from printing
ELSE
obtainedPosition := 1;
END IF;
--SplitString contains the string's splitted return value
SELECT SUBSTRING(:id,:obtainedPosition) INTO SplitString FROM DUMMY;
END;
The above function is modified from http://www.kodyaz.com/sap-abap/sqlscript-reverse-string-function-in-sap-hana.aspx
For string functions in SAP HANA refer to this: http://www.sapstudent.com/hana/sql-string-functions-in-sap-hana/3
You can use anonymous block in SAP HANA to call and check the function
DO
BEGIN
DECLARE id VARCHAR(500) := 'Test-sam-ple-func';
DECLARE delim VARCHAR(2) := '-';
SELECT SCHEMA.FN_SUBSTRING_INDEX(id,delim) AS "SplitStringIndex" FROM DUMMY;
END;
I would be glad to know reason for a downvote. :)