SQL Tutorial: INNER JOIN via USING смотреть онлайн

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Congratulations on making it through the first set of exercises on using INNER JOIN to combine two or three tables into one! You'll next learn about the `USING` keyword in SQL and how it can be used in joins.

Recall the INNER JOIN diagram you saw in the last video. Think about the SQL code needed to complete this diagram. [PAUSE]

Let's check it out. We select and alias three fields and use the left table on the left of the join and the right table on the right of the join matching based on the entries for the id key field.

When the key field you'd like to join on is the same name in both tables, you can use a `USING` clause instead of the `ON` clause you have seen so far.

Since `id` is the same name in both the `left` table and the `right` table we can specify `USING` instead of `ON` here. Note that the parentheses are required around the key field with `USING`.

Let's revisit the example of joining the `prime_ministers` table to the `presidents` table to determine countries with both types of leaders. How could you fill in the blanks to get the result with `USING`? (PAUSE for a few seconds)

Did you get it? (PAUSE for a few seconds)

Ah, I played a bit of a trick on you here. But why does this work? Since an INNER JOIN includes entries in both tables and both tables contain the countries listed, it doesn't matter the order in which we place the tables in the join if we `SELECT` these columns. You'll be told in the exercises which table to use on the left and on the right to avoid this confusion. Note again the use of the parentheses around `country` after `USING`.

Now you'll test your understanding of INNER JOINs before you delve into an exercise with `USING`. Go get 'em!

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