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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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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 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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Can anyone articulate what the key differences are between SAS and SQL? I haven't worked much with SAS but went on a weeks training course, and basically it seemed like the equivalent but more convoluted and was able to do graphs.
Would appreciate some key bullet differences between them.
Standard SQL is a language to query, manipulate and define data in any(!) database. It is like the "latin language" of DB systems. Everyone knows it in order to perform standard tasks. SAS is like an extension to that with many functions.
I found a good document:
http://www.sascommunity.org/mwiki/images/5/52/CMSSUG-0506-SQL.pdf
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I would like to know if there is any problem or any sort of combinations that can not be solved using SQL language.
Is there any list in the web where I can find situations that are impossible to measure using SQL?
Or is everything possible to calculate using SQL.
Thank you.
SQL is pretty flexible, but it can't do everything. However there is no handy guide that I know of that lists what it can't do. There are things that I think you can do but shouldn't: anything that involves doing calculations one row at a time are very inefficient and will generally be faster if done in code.