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The query I decided to feed to the cursor is a very simple query against ), and total duration.I also tried to observe tempdb contention using scripts from Glenn Berry and Robert Davis, but on my paltry system I could not detect any contention whatsoever.Of course I'm also on SSD and absolutely nothing else is running on the system, so these may be things you want to add to your own tests if tempdb is more likely to be a bottleneck.So in the end the queries looked something like this, with diagnostic queries peppered in at appropriate points: , I expected the hit on tempdb pages to be higher with all static variants of the cursor.group by clause – GROUP BY partitions the selected rows on the distinct values of the column on which you group by. Joins are usually more efficient as join rows can be returned immediately, subselects require a temporary work area for inner selects results while processing the outer select. A note worth mentioning over here is that different RDBMS treat this differently – while SQL Server and DB2 do not allow more than one NULL value in a unique index column, Oracle allows multiple NULL values.
EXISTS sub selects doesn’t need any to specify values. 2) How to determine when the commit needs to be done . Both can be declared on one or more columns, both can be used to enforce foreign keys (if the unique index is on not null column(s)), both can be declared as clustered/non clustered indexes (SQL Server lingo), both can be used on computed columns as well (SQL Server). 1) What are the process to be followed when you are adding a new table. Performance tuning in DB2 what are the factors you should consider while creating a new DB2 table Deadlock in Db2 and work arounds to avoid deadlocks What factors affect the lock duration Different SQLcodes that you should handle in COBOL programs SQLCODE if BIND not performed, SQLCODE if table is missing What is the difference between a Primary Key and a Unique Index?For a normalized relation, there is one designated primary key.Unique index: a physical object that stores only unique values.