问题
How does one do this? The SYSCOLUMNS system table only has columns for tables. SYSCHECKS has a REFERENCEDCOLUMNS object. Is there any way to get this.
I'm aware of the JDBC getPrimaryKeys call, but that doesn't get unique constraint columns.
回答1:
Derby - constraints
It took some digging to find the above question; my question is a partially answered follow-up question to the one above.
Taking the CONSTRAINTID against SYSKEYS gives a CONGLOMERATEID, which when taken against SYSCONGLOMERATES yields a DESCRIPTOR. The DESCRIPTOR is a POJO that contains an int-array in the baseColumnPositions method. This int-array contains the COLUMNNUMBERS in SYSCOLUMNS of the columns in the constraint.
If querying in straight SQL, getting the DESCRIPTOR field yields a string with a CSV list of ints that have to be parsed. Fortunately for me, I happen to be working in Clojure, so calling the baseColumnPositions method and using the resulting int-array are trivial.
来源：https://stackoverflow.com/questions/2349785/how-to-get-primary-key-and-unique-constraint-columns-in-derby