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In other words, are there any scenarios in which GROUP or ORDER are used without being immediately followed with BY?
In SQL, the keywords are stated as;
ORDER BY, and not ORDER, and so goes it for GROUP. It's only identified as GROUP BY in its syntax.
I guess it may have a historical reason, the creators of the original SQL wanted it(SQL's syntax) to be more similar to English instead of a programming language(like C).
So, I guess again it's safe to think as GROUP BY as if it's group_by in C(assuming C has some group_by routine), Same for ORDER BY.
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What has better (faster) performance?
mycolumn::character(1)='4' or mycolumn like '4%'
where mycolumn is text or character(200)
It is often quite simple to do these tests yourself to see which is faster.
As a general rule, though, like with constants starting the pattern is index-friendly. That means that it would generally be the preferred solution.
Even without an index, like appears to perform better, as this example in db<>fiddle shows. Of course, working on this artificial data does not mean that it would have the same performance characteristics on your data.
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I've always struggled with how to format SQL queries in terms of whitespace, alignment, etc. It seems whenever there is an "auto-formatter" it seems to format things differently than the next one, whether it is within a SQL client or a website or text-editor that does various language formatting. Are there any guideline(s) for how SQL should be formatted for best readability? Here is an example of how I currently do it:
SELECT
name
FROM
sales_instance si
JOIN main_iteminstance i ON si.instance_id=i.id
ORDER BY
name
Also, yes I know this may be 'opinion-based' and people may want to close it for that, but I think this answer is helpful as to writing clean SQL and hopefully someone can provide a good summary of the available formats or guidelines.
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I am curious if one can see the internal mechanism of merge join or any other join sql?
For Oracle have a look at this document: Database SQL Tuning Guide - Joins
If you are thinking about how they work, you can look it up here, it's a great representation of it.
If you are thinking about the code behind it, I think you'll have to work for MS to access it ;)
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I know that SQL is different in various databases. But I need to know which functions are predicates in source SQL as language standart (not vendor solutions).
I found:
CONTAINS
EXISTS
IS NULL
IS NOT NULL
Is it all? Or did I lose smth?
Are all predicates use the TVL?
P.S. Sorry if I wrote stupidity, I'm a noobie in the database but I need to know it for exam.
You can refer here:
ANSI SQL Framework
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In which version of Oracle is over clause is present? What is the purpose of this clause?
The OVER clause specifies the partitioning, ordering & window "over which" the analytic function operates
Reference:
OVER clause in Oracle