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visits member for 2 years, 3 months
seen Jul 18 at 6:47

Jul
14
comment Slow DELETE in MySQL with a subquery
Aaaaargh. stackoverflow.com/questions/45494/… Apply solutions suggested over there or switch to a better dbms.
May
19
comment How to SELECT multiple COUNT(*) columns with each GROUP BY having a different WHERE clause?
Are you sure RIGHT outer join is the correct thing to use ?
Apr
1
comment Find actual data size from a query?
"Size" is not a property of "data".
Jan
3
comment An example of a relation without any functional dependency?
You should strike through that incorrect sentence where you say "yes, I believe". Then what remains is the correct answer.
Jan
3
comment Find the highest graded student, using Tuple Relational Calculus
"Tuple relational calculus does not have a set difference operator"
Oct
9
comment How to get performance benefits from a view vs subquery?
More importantly, if a CTE is referenced multiple times, this fact by itself is not sufficient to deduce that the optimal access paths for each of the contexts in which they appear are also identical. Think any CTE, with attributes say A and B, being tested once for "does it contain a tuple where A=1" and elsewhere being tested for "does it contain a tuple where B=7". The CTE is the same, the optimal access paths for the two usages of the CTE most likely aren't, and neither of them necessarily involves full evaluation.
Apr
3
comment Handling expiration in a course registration or ticketing system
And in addition, create views such as REGISTRATION_EXPIRED_WITHOUT_PAYMENT and REGISTRATION_UNPAID_UNEXPIRED.
Mar
13
comment Representing SQL constraints on a table
Chris, The accepted answer in that post does not give a declarative solution, and the answer by AKuznetzov forces three extra columns upon the user, and I'm not sure it is entirely impossible for the user to have the integrity test fail because of mistakes in those extra three columns.
Mar
12
comment Representing SQL constraints on a table
Even if he dropped the floor condition, can he have his constraint enforced declaratively with those engines that you mention ?
Mar
2
comment Why is optimistic locking faster than pessimistic locking?
No it doesn't. That's why it's "faster".
Feb
20
comment Database functional dependency BCNF help
As far as normal forms theory is concerned, yes. As far as logical database design is concerned, remember that xNF is not where the story ends.
Feb
18
comment ORDER BY clause is allowed over column that is not in SELECT list?
Or it wouldn't. A table is explicitly defined by the standard to be an "unordered collection of rows". Make that fit with ORDER BY clauses ...
Feb
18
comment ORDER BY clause is allowed over column that is not in SELECT list?
For the problem the OP describes, just putting the ORDER BY before the SELECT will do the job. Don't read too much into these kinds of "flowcharts of query processing". They are rarely intended for being 100% accurate and complete. Rather, they are intended for illustrating somewhat globally what goes on as a consequence of an SQL statement being issued.
Feb
1
comment What is the correct result for this query?
@Kevin did you ask ISO for permission to copy ? :-)
Jan
29
comment What is the correct result for this query?
Well the key issue is whether it's indeed true that "even if the table has no rows at all, it's still one group of 0 rows". And the standard turns out to be explicit about this : "If there are no grouping columns, then ... is the grouped table consisting of T as its only group". (and that holds even if T is empty - so there is indeed a group.) Further on, the having clause specifies that the condition is applied to each group (in the example thus once). They probably defined it this way to make SUM and COUNT return one row even for empty T's.
Jan
24
comment How to tackle a large undocumented database
Think before you comment. The OP explicitly stated that he was the ONLY It guy. So who are those developers ? External contractors perhaps, who were paid for nothing more than just the time it took to build the thing ? Why would those be willing to put in their time for additional support, which company X probably has been unwilling to pay for to begin with ? Or were they perhaps former employees who got laid off because they were too expensive ? Why would they put in their time to help out company X with its problems ? And who is going to get hurt by dropping tables ?
Dec
14
comment Simplify and optimize a complex query
Then you'll have to make the users accept the 35 seconds (and its further degrading as data volumes grow faster than the hardware speeds do). Forewarning them about this (as in : display a rotating clockwork to make it clear that the machine is working at their service) sometimes works miracles in this respect.
Dec
11
comment Searching transaction logs for changes
you'll have to specify which SQL product you're using.
Dec
3
comment How to best encapsulate monetary values in a database
Option 1 is not anti-relational and it is not true that there isn't a "purely relational solution to this". Except then perhaps for extremely perverse interpretations of "purely relational".
Nov
2
comment “Zero” downtime and minimal space requirements for upgrade to PostgreSQL 9.2
Providing only version numbers without naming the product isn't exactly helpful ...