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Exercise #16 (tips and solutions)

Redundancy decision 1.12.2 can be eliminated, if to remove the subquery and create join between tables P and L. In this case, the request will not only compact, but easily readable and, most importantly, more effective.

Here is an example of a hard to read, although the correct solution, which is published on the site's forum:

Console
Execute
  1. SELECT MAX(model1), MIN(model2), MAX(speed), MAX(ram) 
  2. FROM (SELECT pc1.model AS model1, pc2.model AS model2, pc1.speed, pc2.ram, 
  3.              CASE WHEN CAST(pc1.model AS NUMERIC(6,2)) > 
  4.                        CAST(pc2.model AS NUMERIC(6,2)) 
  5.                   THEN pc1.model+pc2.model  
  6.                   ELSE pc2.model+pc1.model  
  7.              END AS sm 
  8.       FROM PC pc1, PC pc2 
  9.       WHERE pc1.speed = pc2.speed AND 
  10.             pc1.ram = pc2.ram AND 
  11.             pc1.model <> pc2.model
  12.       ) a 
  13. GROUP BY a.sm;

I think this is a good example of not good queries.

To return to discussion of exercise #16

To solve a problem on SQL-EX.RU
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