3-Table SQL Inner Join: How to Join Tables with SQL

In SQL, joining tables is a common operation performed to combine data from multiple tables into a single result set, based on a specified condition. The Inner Join is one of the most common types of joins used when working with SQL databases.

├Źndice
  1. What is an Inner Join?
  2. Conclusion

What is an Inner Join?

An Inner Join is a type of join that returns only the rows that have matching values in both tables being joined. In other words, it combines the data from two or more tables based on a specified condition, and only returns the rows where the condition is true.

Joining three tables in SQL is no different from joining two tables, the only difference being that you need to specify an additional join condition. To join three tables using SQL's Inner Join, you need to use the following syntax:

SELECT table1.column1, table2.column2, table3.column3
FROM table1
INNER JOIN table2 ON table1.column=table2.column
INNER JOIN table3 ON table2.column=table3.column;

In the above example, we are selecting columns from three tables, and joining them using the Inner Join. The first join condition is between table1 and table2, and the second join condition is between table2 and table3.

When joining three or more tables, it's important to specify the join conditions correctly, otherwise, you may end up with unexpected results or errors. You can use aliases to simplify the syntax and make it more readable, like this:

SELECT t1.column1, t2.column2, t3.column3
FROM table1 t1
INNER JOIN table2 t2 ON t1.column=t2.column
INNER JOIN table3 t3 ON t2.column=t3.column;

Using aliases makes the SQL statement easier to read, and helps to avoid confusion when working with multiple tables.

Conclusion

In conclusion, joining tables in SQL is a powerful feature that allows you to combine data from multiple tables into a single result set. The Inner Join is a common type of join used in SQL, and is used to return only the rows that have matching values in both tables being joined. When joining three or more tables, it's important to specify the join conditions correctly, and using aliases can make the syntax more readable.

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