ANSI 92 Recursive SQL Statement required

Question

I am translating SQL Server SQL Statements into their ANSI generic equivalent at present, and am stuck with a recursive statement using a WITH statement.

For the sake of concentrating on the issue, I'll simplify the issue as follows

If I have two tables

1. ReportingUnit

   • col1: Key
   • col2: ParentReportingUnitKey

2. Facility

   • col1: Key
   • col2: ParentReportingUnitKey

This structure is describing a hierarchy of reporting units down to a facility, where a reporting unit may have 0 .. 1 direct parent reporting units and 0 .. n child reporting units.

A facility is a 'leaf' record, that links to a reporting unit.

I need to craft an ANSI 92 valid SQL Statement (or at worst one that will work on Oracle, DB2 and SQL Server) that will return all facilities related to a given reporting unit anywhere up the hierarchy.

e.g.

• ReportingUnit R1 has ReportingUnit children R1.1 and R1.2
• ReportingUnit R1.1 has children R1.1.1, R1.1.2

• ReportingUnit R1.2 has children R1.2.1, R1.2.2

• Facility F1 has a parent reporting unit R1.1.1

• Facility F2 has a parent reporting unit R1.1.2
• Facility F3 has a parent reporting unit R1.2.1
• Facility F4 has a parent reporting unit R1.2.2

Bearing in mind there are may be 0 .. n levels of recursion in the ReportingUnit table, how can I return all 4 facilities from a SQL Statement given the parameter ReportingUnit=R1?

Answer 1

I'm tolerably certain that no recursive statements were available in SQL-92; the earliest version where that was supported was SQL-99.

Consequently, you are stuck with not using SQL-92. Why do you think SQL-92 is desirable? Is it as a base level of SQL functionality, or is there some other reason?

Current versions of DB2 have the WITH clause and can achieve recursive queries. I believe Oracle has the WITH clause too; I'm not sure whether it can achieve recursive queries using them. Oracle also has the wholly non-standard and non-relational CONNECT BY PRIOR. I'm not sure what MS SQL Server supports.

There is a reasonably strong chance that you will be unable to find a single syntax that is supported by all three of your specified DBMS.

Answer 2

There is no SQL-92 solution for recursive queries.

The best option is to use one of the solutions for encoding hierarchical relationships so that you can query all descendants or ancestors, using standard SQL.

See a brief description here: "What is the most efficient/elegant way to parse a flat table into a tree?".

Or read "Trees and Hierarchies in SQL for Smarties" by Joe Celko.