Explicit and Implicit LIST Aggregate Function for Relational Databases: Explicit and Implicit LIST Aggregate Function for Relational Databases Witold Litwin Université Paris 9 Dauphine mailto:Witold.litwin@dauphine.fr


Summary: Summary New Aggregate Function Transforms a set of values into single one Char type A basic long time need Should be highly useful


Plan: Plan Motivating Examples Explicit LIST Implicit LIST Conlusion Further Work


Motivating Example 1: Motivating Example 1 The Supplier-Part (SP) table of the best-known S-P database


Motivating Example 1: Motivating Example 1 The classical query : select SP.[S#], Sum(SP.Qty) AS [Total Qty] from SP group By SP.[S#]; S# Total Qty S1 1300 S2 700 S3 200 S4 900 How to get also the individual quantities ?


Motivating Example 2: Motivating Example 2 A database of persons having: Multiple Hobbies Multiple preferred Restaurants Many Friends Best design: four 4-NF tables P (SS #, Name), H (SS#, Hobby), R (SS#, Rest), F (SS#, Friend)


Database: Database


Fragment: Fragment


Query: Query select P.[SS#], P.Name, F.Friend, R.Rest, H.Hobby from ((P INNER JOIN F ON P.[SS#] = F.[SS#]) INNER JOIN H ON P.[SS#] = H.[SS#]) INNER JOIN R ON P.[SS#] = R.[SS#] where P.[SS#] ="ss1" ; Select Name, Friends, Restaurants, Hobbies, of Person ‘SS1’ SQL :


Result: Result Usable ???


General Problem: General Problem Current RDBs manage tables in 1NF All attributes are single-valued (atomic values) Example 1 ; We wished Single-valued attribute : SUM(QTY) Multi-valued attribute Individual quantities The result would not be 1NF


General Problem: General Problem RDB manages tables in 1NF All attributes are single-valued Example 2 ; We wished : Single-valued attributes : S#, Name Multi-valued attributes (multi-sets): Hobby, Rest, Friend The result is normalized to 1NF {(ss1,Witold, x, y, z) : x  Hobby, y  Rest, z  Friend } The table is not in 4NF Subject to well-known anomalies


Solutions: Solutions Design RDBS for 0NF tables A revolution 0NF RDBS will not be here for years Aggregate set or multi-set values into atomic values An evolution All RDBS already do it using: SUM, AVG, COUNT… perhaps with GROUP BY We need a new aggregate leaving the entire set visible E.g: (multi)-set of values X => (single) list of values X


Local Culinary Example: Local Culinary Example The set-valued attribute: (Schwarz, Wälder; Kirchen, Chocoladen, Torte) The aggregated attribute: Schwarzwälderkirchenchocoladentorte Local specialty, try it !


Explicit LIST function: Explicit LIST function Select S#, sum (Qty) AS [Total Qty], LIST (Qty) AS Histogram from SP group by S#;


Explicit LIST function: Explicit LIST function select P.SS#, Name, LIST (DISTINCT (Friend)), LIST (DISTINCT (Rest)), LIST (DISTINCT (Hobby)) from P, F, R, H where P.SS# = F.SS# and F.SS# = R.SS# and R.SS# = H.SS# and P.SS# ="ss1" group by P.SS#, Name ;


Explicit LIST function: Explicit LIST function Simulated actual output using MsAccess forms with list boxes Form with three subforms No SQL query used


Explicit LIST function: Explicit LIST function select P#, SUM (Qty) as [Total Qty], LIST (S#, Qty) as [Per supplier] from SP group by P#;


Implicit LIST function: Implicit LIST function For any single-valued A : A = LIST (A) Any non-aggregated attribute in an SQL query has to be in the GROUP BY clause Now, any non-aggregated perhaps composite attribute A from a single table and not in GROUP BY clause is implicitly under LIST (DISTINCT (A)) Queries may become less procedural


Implicit LIST function: Implicit LIST function select P#, SUM (Qty) as [Total Qty], S#, Qty from SP group by P# having ‘S# QTY’ like ‘*s4*’; Implicit LIST is LIST (S#, QTY)


Implicit LIST function: Implicit LIST function Query Select S.*, P#, Qty From S, SP Where S.S# = SP.S# Repeats all the data of the supplier S in every resulting tuple 6 times for S1: its Name, City, Status Query Select S.*, P#, Qty From S, SP Where S.S# = SP.S# Group By S.S# Does it only once per supplier Less redundancy


Implicit Joins and From: Implicit Joins and From Equijoins following the referential semantic links or integrity may be implicit MsAccess, SQL Server… FROM clause content can be inferred from the attribute names Even less procedural formulation may result: select P.SS#, Name, Friend, Rest, Hobby group by P.SS#, Name ;


Implementation Issues: Implementation Issues Should be easy for the RDBS owner Any RDB already processes the aggregates Already done hiding the list Should also be shown


Implementation Issues: Implementation Issues For explicit LIST, foreign function interface may suffice Oracle, DB2, Yukon… See related work in the paper for current (limited) proposals Oracle & iAnywhere (core code) Not for the implicit LIST Access to core code is necessary


Conclusion: Conclusion LIST is a new aggregate function Aggregates a multi-valued attribute into a single value Responds to a long-standing fundamental RDBS user need - 30 years ? Should be rather easy to implement Future work should start with the implementation Using foreign functions for explicit LIST


Research Support : Research Support European Commission ICONS Project no. IST-2001-32429. Microsoft Research


Thank You for Your Attention: Thank You for Your Attention Witold Litwin Université Paris 9 Dauphine mailto:Witold.litwin@dauphine.fr