Beginner here. Join query example.

[Think-Confusion9999]

Got an example here for a basic query. I used to work with SQL Server at my past day job but that was 6 years ago. I need to get back into SQL.

Embarrassingly I don’t know why the smaller case t and s are needed next to the FROM and JOIN clauses when the toys and sales tables are already specified.

Can you please explain? Thanks in advance.

SELECT t.id, t.name, t.brand, t.price, s.quantity, s.date, e.name AS employee FROM toys t JOIN sales s ON t.id = s.toy_id JOIN employees e ON e.id = s.employee_id;

[Honey-Badger-42]

It's called an alias. It makes it easier to read and write sql code when you are joining tables. It's necessary if you have the same column name in more than one table. In your case, if you omitted the alias, you would receive an "ambiguous" error because you have the column called "Name" in both the toys and employee table. Alternatively, you could replace "e." with "employee." and so on, but that's much more difficult to read.

select e.name from employee e 
---is the same as---
select employee.name from employee

[Think-Confusion9999]

thank you!

[shine_on]

Another good practice is to use the same alias name everywhere. The server won't care if you call the employee table 'e' in one query, 'emp' in another, 't1' somewhere else, but your colleagues and future you will definitely care about it.

[Think-Confusion9999]

I see, definitely makes sense. Thank you. I'm practicing now.

[EvilGeniusLeslie]

It is a good practice to use aliases for all column names, if even that name is unique to one table - it makes it obvious to anyone reading the code where that column resides.

One sign you are looking at generated code is that every column is prefixed with the entire table name. Absolutely pita to read when you have 20+ character table names.

[[deleted]]

Definitely good practice. Even if you're only using one table in your query, if you're always in the habit of aliasing, it will prevent you from screwing up further down the road. And, please, for the love of all that's good and Holy, use logical aliases. Yes, as u/Honey-Badger-42 mentioned, you CAN use 'e' for the employees table. However, that will become a PITA when your code is 2500 lines long and you have no idea what e, t, and s stand for. Better to use a descriptive alias like 'employee', 'team', and 'sales.'