[Joe Celko’s Dataflow Diagrams Puzzle]
Tom Bragg posted a version of this problem on the CASE Forum on CompuServe. You have a table of dataflow diagrams (DFDs), which has the name of the diagram, the names of the bubbles in each diagram and the labels on the flow lines. It looks like this:
CREATE TABLE DFD (diagram CHAR(10) NOT NULL, bubble CHAR(10) NOT NULL, flow CHAR(10) NOT NULL, PRIMARY KEY (diagram, bubble, flow));To explain the problem, let’s use this table:
DFD diagram bubble flow ========================= Proc1 input guesses Proc1 input opinions Proc1 crunch facts Proc1 crunch guesses Proc1 crunch opinions Proc1 output facts Proc1 output guesses Proc2 reckon guesses Proc2 reckon opinions …What we want to find is what flows. Do NOT go into each bubble within the diagrams. This will be part of a diagram validation routine that will search for missing dataflows. To make this easier, assume that all bubbles should have all flows. This would mean that (Proc1, input) is missing the ‘facts’ flow, and that (Proc1, output) is missing the ‘opinions’ flow.
We could use this SQL-92 query:
SELECT F1.diagram, F1.bubble, F2.flow FROM (SELECT F1.diagram, F1.bubble FROM DFD AS F1 CROSS JOIN SELECT DISTINCT F2.flow FROM DFD AS F2) EXCEPT SELECT F3.diagram, F3.bubble, F3.flow FROM DFD AS F3 ORDER BY F1.diagram, F1.bubble, F2.flow;Basically, it makes all possible combinations of diagrams, and flows, then removes the ones we already have. The bad news is that you will probably have to do this with VIEWs in most current SQL products.
Another SQL-92 query would be:
SELECT F1.diagram, F1.bubble, F2.flow FROM (SELECT F1.diagram, F1.bubble FROM DFD AS F1 CROSS JOIN SELECT DISTINCT F2.flow FROM DFD AS F2 WHERE flow NOT IN (SELECT F3.flow FROM DFD AS F3 WHERE F3.diagram = F1.diagram AND F3.bubble = F1.bubble) ORDER BY F1.diagram, F1.bubble, F2.flow;Or to answer the puzzle in SQL-89, you will need to use VIEWs:
— build a set of all the flows CREATE VIEW AllDFDFlows (flow) AS SELECT DISTINCT flow FROM DFD; — attach all the flows to each row of the original table CREATE VIEW NewDFD (diagram, bubble, flow, missingflow) SELECT DISTINCT F1.diagram, F1.bubble, F1.flow, F2.flow FROM DFD AS F1, AllDFDFlows AS F2 WHERE F1.flow <> F2.flow; — Show me the (diagram, bubble) pairs and missing flow — where the missing flow was not somewhere in the flow column — of the pair. SELECT DISTINCT diagram, bubble, missingflow FROM NewDFD AS ND1 WHERE NOT EXISTS (SELECT * FROM NewDFD AS ND2 WHERE ND1.diagram = ND2.diagram AND ND1.bubble = ND2.bubble AND ND1.flow = ND2.missingflow) ORDER BY diagram, bubble, missingflow;I probably overdid the DISTINCTs, but you can experiment with it for execution speed. This should still run faster than moving all the rows across the network.
Puzzle provided courtesy of: