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Asked: 2024-09-26T23:01:20+05:30 In:

How can I update several rows in a single SQL statement with different values for each row? What is the correct syntax or approach for achieving this in a database?

I’ve been diving into SQL for a bit, and I came across this situation that I can’t quite wrap my head around. So, let’s say I’ve got a table called `employees`, and it’s got a bunch of columns like `id`, `name`, and `salary`. Right now, I need to update the salaries for several employees in a single SQL statement. The catch is that each employee is getting a different raise amount – it’s not a one-size-fits-all situation.

I was reading about using the `UPDATE` statement and thought, “Hey, I could just run multiple `UPDATE` queries to handle each employee one at a time.” But then I realized how clunky that would be! I mean, who wants to execute five different queries when you can do it all in one right? Time-saving is key, especially when I’m working with larger datasets.

So, what I really want to know is if there’s a way to do this cleanly in one statement. I’ve heard people talking about some syntax that allows for this, but when I tried to look it up, I started getting confused with all the different methods out there. Like, do I need to use `CASE` for different values? Or is there another way that I’m just completely missing?

It would be super helpful if someone could break this down for me. What’s the best approach to update several rows with different values without losing my mind or making my SQL server work overtime? Also, if there’s any difference in how this works depending on the SQL database (like MySQL vs. PostgreSQL), that would be good to know.

I’d love to hear how you all handle this kind of situation and what tips or tricks you’ve learned along the way! It could be a lifesaver not just for me but for anyone else out there facing the same dilemma. Thanks in advance!

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    2 Answers

    1. It sounds like you’re diving into an interesting situation with SQL! You’re right in thinking that running multiple UPDATE statements can be super clunky. Luckily, there’s a cleaner way to update multiple rows with different values using a single UPDATE statement!

      The trick is to use a combination of the UPDATE statement along with a CASE expression. This allows you to specify different values for each employee in a single query. Here’s a simple example:

      
UPDATE employees
SET salary = CASE id
    WHEN 1 THEN salary + 1000
    WHEN 2 THEN salary + 1500
    WHEN 3 THEN salary + 1200
    ELSE salary
END
WHERE id IN (1, 2, 3);

      In this example, you’re updating the salary for employees with IDs 1, 2, and 3, each with a different raise amount. The ELSE salary part ensures that if an employee ID doesn’t match, their salary remains unchanged.

      Now, about the differences in SQL databases—you’ll find that most SQL databases like MySQL, PostgreSQL, and SQL Server support this CASE syntax in an UPDATE statement. Just be cautious if you’re working with something like SQLite since it has a bit of a different syntax for updates.

      Also, if you’re keen on performance, a single query is always going to be more efficient than multiple queries, especially with larger datasets, like you mentioned!

      Overall, using CASE for different values in a single UPDATE statement is definitely the way to go. It keeps your code clean and saves you from running around with multiple queries. Hope that helps clear things up a bit for you!

    2. To update salaries for multiple employees in a single SQL statement, you can use the `CASE` statement within your `UPDATE` query. This method allows you to specify different raise amounts for each employee in a clean and efficient manner, avoiding the need for multiple separate queries that can clutter your code and slow down execution. The syntax would look something like this:

      UPDATE employees
SET salary = CASE id
    WHEN 1 THEN salary + 5000
    WHEN 2 THEN salary + 3000
    WHEN 3 THEN salary + 7000
    ELSE salary
END
WHERE id IN (1, 2, 3);

      This code checks the `id` of each employee and applies the corresponding raise. Note that ‘ELSE salary’ ensures that if an `id` doesn’t match, the salary remains unchanged, and the `WHERE` clause limits the update to the specified employees. While this approach is generally supported in many SQL databases like MySQL and PostgreSQL, it’s crucial to check the documentation for any specific nuances or constraints based on the SQL server you’re using. With this technique, you can efficiently manage multiple updates in one execution, saving both time and server resources.

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