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When to use distinct option in select statement?
Many people use the DISTINCT option in a select statement to filter out duplicate results from a query’s output. Take this simple PUBS database query as an example: In a simple select from one table (like the one above) this is the easiest and quickest way of doing things.
When to use distinct as the default qualifier?
That said, some people (Chris Date, for example) argue that DISTINCT should be the default qualifier for SELECT; we should have to write SELECT ALL to return a non-relational result (relations do not contain duplicate tuples by definition). My view is that there is nothing inherently wrong with SELECT DISTINCT.
Is it true that SELECT DISTINCT is returning duplicates?
Select Distinct is returning duplicates Our community of experts have been thoroughly vetted for their expertise and industry experience. Experts with Gold status have received one of our highest-level Expert Awards, which recognize experts for their valuable contributions. More years at various grindstones than I care to remember.
Is it possible to speed up SELECT DISTINCT queries?
The query will work as required, but we can get a small performance improvement if we write it like this:
Why is my SELECT DISTINCT query so slow?
Pretending that I’m 100% certain the DISTINCT portion of the query is the reason it runs slowly, I’ve omitted the rest of the query to avoid confusion, since it is the distinct portion’s slowness that I’m primarily concerned with (distinct is always a source of slowness). The table in question has 2.5 million rows of data.
How to speed up SELECT DISTINCT queries in pubs?
Take this simple PUBS database query as an example: In a simple select from one table (like the one above) this is the easiest and quickest way of doing things. However, with a more complex query you can think about re-coding it to gain a performance advantage. Take this example query, which only returns authors that have a book already published.
How many rows does a distinct query need?
The table in question has 2.5 million rows of data. The DISTINCT is needed for purposes not listed here (because I don’t want back a modified query, but rather just general information about making distinct queries run faster at the DBMS level, if possible).