Re: boolean logic expressed in RDBMS rows

>> How about this idea? Express each conditions by EXISTS(correlated
subquery), then AND/OR each EXISTS(). <<

I think what he is after is the ability to load tables with criteria and not have to use dynamic SQL:

skill = Java AND (skill = Perl OR skill = PHP)

becomes the disjunctive canonical form:

(Java AND Perl) OR (Java AND PHP)

 which we load into this table:

CREATE TABLE Query
(and_grp INTEGER NOT NULL,
 skill CHAR(4) NOT NULL,
 PRIMARY KEY (and_grp, skill));

INSERT INTO Query VALUES (1, 'Java');
INSERT INTO Query VALUES (1, 'Perl');
INSERT INTO Query VALUES (2, 'Java');
INSERT INTO Query VALUES (2, 'PHP');

INSERT INTO Candidates VALUES ('John', 'Java'); --winner
INSERT INTO Candidates VALUES ('John', 'Perl');
INSERT INTO Candidates VALUES ('Mary', 'Java'); --winner
INSERT INTO Candidates VALUES ('Mary', 'PHP');
INSERT INTO Candidates VALUES ('Larry', 'Perl'); --winner
INSERT INTO Candidates VALUES ('Larry', 'PHP');
INSERT INTO Candidates VALUES ('Moe', 'Perl'); --winner
INSERT INTO Candidates VALUES ('Moe', 'PHP');
INSERT INTO Candidates VALUES ('Moe', 'Java');
INSERT INTO Candidates VALUES ('Celko', 'Java'); -- loser
INSERT INTO Candidates VALUES ('Celko', 'Algol');
INSERT INTO Candidates VALUES ('Smith', 'APL');  -- loser
INSERT INTO Candidates VALUES ('Smith', 'Algol');

The query is simple now:

SELECT DISTINCT C1.candidate_name
  FROM Candidates AS C1, Query AS Q1
 WHERE C1.skill = Q1.skill
 GROUP BY Q1.and_grp, C1.candidate_name
HAVING COUNT(C1.skill)

• (SELECT COUNT(*) FROM Query AS Q2 WHERE Q1.and_grp = Q2.and_grp);

You can retain the COUNT() information to rank candidates. For example Moe meets both qualifications, while other candidates meet only one of the two. Received on Tue May 13 2003 - 02:42:42 CEST