I am learning SQL from a class online.
I wanted to ask if it's generally best to use LIMIT in my queries to make them run faster, or at least until I have them tested and pulling the right data.
If yes, where should I put it in the order of things? Does it need to go at the very end, or does it depend on what kind of SQL software I'm using?
Thanks a lot for your help!
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The only answer to this is "It Depends". I mean if you want to get a sample couple of rows from a table to view what the data looks like, then use limit but otherwise you usually have requirements for a specific query which you build. Using limit on a specific query doesn't help you to determine if its working or not and you shouldn't be running queries against a live production database, so it won't matter how long it takes.
And as to where does it goes, the documentation shows you how to use limit.
As to what kind of SQL software you are using - you would have to explain further. SQL isn't software, its a query language - which is determined by the RDBMS (MySQL) you are using, not (generally) the client software you are using to interact with it.
@DaleK nailed it with the "it depends". If you have only added 5 records to your database, a limit clause makes little sense - except to experiment with it and learn how to use it. On the other hand if you have a million records and don't know how many will be returned by a specific query, then a limit clause makes sense, especially if your terminal is slow or buffers all scrollback.
Understand what you are using limit for. It doesn't speed up a query, the full query takes place, you are just limiting the number of records shown. Very helpful if you want to look at the "top ten" of some query, or the last record entered, etc..
As for should you use it "generally"? Well, no, you don't just add it "just because". You add it when you need it like any other query modifier. Good luck with your SQL!
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Really as an comment - but discussions don't do comments:
It doesn't speed up a query, the full query takes place, you are just limiting the number of records shown.
Thats not strictly true... if the query only has to grab the first 10 records it will certainly be faster than pulling 1000 records - so long as the ordering matches an index. However if the ordering requires a complete table scan, then thats a different matter.
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Yes, using LIMIT is generally a good idea, especially when:
Testing or debugging a query and you don't need the full dataset.
Verify that your joins, filters, or computed columns return the expected results.
Working on a large table, and fetching all rows could impact the performance.
In terms of your 2nd question (where should I put it in the order):
SELECT *
FROM employees
WHERE department = 'HR'
ORDER BY employee_id DESC
LIMIT 10; -- <<< at the very end of the query
The question is obviously opinion-based. I think LIMIT doesn’t automatically make a query faster — it just caps how many rows are returned, not necessarily how many are scanned or sorted.
It can improve speed if combined with an indexed ORDER BY clause or a selective WHERE clause.
But if the query still needs to read or sort most of the table, LIMIT won’t help much.
For real performance gains, use indexes on filter/sort columns, narrow your WHERE clause, and avoid unnecessary sorting or joins — those reduce the actual work the database must do.
Regarding "does it go at the very end" does depend on the brand of SQL you're using.
LIMIT isn't actually standard SQL, so no brand is obligated to implement this feature.
AFAIK, it's implemented by MySQL, PostgreSQL, and SQLite, and forks or workalikes of those three.
Other brands have different syntax to do a similar operation. Like SELECT ... FETCH FIRST x ROWS ONLY in Oracle SQL or SELECT SKIP x FIRST y ... in Informix.
This is an important thing to keep in mind as you're learning: despite the fact that SQL is an ANSI/ISO standard, every brand implements SQL differently. So you need to be clear about which brand and which version you're using, and study the documentation for that specific brand.
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I would circle back to say, while you are learning SQL don't even think about these sort of things. SQL is a large and complex subject - just work on finding a solution which solves your immediate problem without attempting any form of optimisation or cleverness. You really need to understand the basics before you have enough context to make good decisions about all that and as your understanding grows, the more complex aspects will start to make more sense naturally.
