While it’s a somewhat dated practice, this is still perfectly valid and executes the same as a JOIN written as an INNER JOIN. The general syntax of a SQL Server JOIN statement is: I ’ve helped so many customers over the years improve the through p ut on their SQL Server installations by simplifying their JOIN statements. Simpler is better when it comes to JOINs. As I’ll show later, the more complex the SQL statement is, the bigger the chance the query optimizer w on’t produce a good execution plan. Lastly, it ’s worth mentioning although SQL Server allows you to write highly complex JOIN statements in volving many tables, it does n’t mean you should. There are a few things to note about this tutorial. Firstly, while it ’s possible to JOIN multiple tables for data modifications (INSERT/UPDATE/DELETE), for simplicity’s sake, I’ll stick to SELECT statements. Secondly, I’ll focus on using tables and views as sources. While you can use the APPLY operator to perform similar functionality as JOIN statements involving table-valued user-defined functions, I’ll leave that explanation for another SQL tutorial. Many of the examples below use the AdventureWorks database. This tutorial covers when and why to use certain types of join s and some common pitfalls developers encounter when writing SQL Server JOIN statements. Generally, when we think of joining tables together, we think of returning data from two tables w ith an equality match (INNER JOIN) between the sources. However, the JOIN keyword also has options for returning all the data from one table and only the records match ing from the other table (OUTER JOIN). The JOIN syntax is an optional part of the FROM statement and is used to specify how to return data from different tables (or views).
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