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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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When a U.S. address is stored, obviously it needs to have the state stored as well. The issue is that the word "State" is a reserved keyword in SQL.
What else should this be named? Are there any alternatives or do people just deal with having to wrap it in square braces?
Personally we prefer to use State as the property name and wrap it in queries or anywhere else there may be reserved word conflicts. We have not had any issues with this in the 3 years I have been on the team. Hope that helps!
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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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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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There is so many option in each programming languages which can be mentioned in the code documentation.
I want to know what are the most important Items which we have to document?
I'd document contracts (this parameter is expected not to be null, this function never returns null, ...) as well as the meaning (this method does that, ...). Besides documenting the API, I'd add comments on pieces of code which are non-trivial but add a significant value to the application (cryptic but real fast, works around a framework bug).
What you document ultimately depends a lor on who will read that documentation...