SUBSTRING in a SELECT-Statement

Hello,

on the "Support Facility"-site I want to execute a query:

SELECT jd.Name, jdp.DefaultExpression from JobDefinition jd, JobDefinitionParameter jdp where jd.UniqueId=jdp.JobDefinition where jdp.Name='ABAP_PROGRAM_NAME'

That's working fine.

But I need only the left 8 characters of the DefaultExpression, but

SELECT jd.Name, SUBSTRING (jdp.DefaultExpression,1,8) from JobDefinition jd, JobDefinitionParameter jdp where jd.UniqueId=jdp.JobDefinition where jdp.Name='ABAP_PROGRAM_NAME'

doesn't work.

How can I manipulate the String "DefaultExpression" in the query?

Best regards

Dana