MySQL Joins: ON vs. USING: When Should I Use Which?

MySQL Joins: ON vs USING

MySQL provides two ways to perform joins: ON and USING. Understanding the subtle differences between these two syntaxes can help optimize your queries.

ON

ON is the more versatile option. It allows you to join tables on a single column, multiple columns, or even a condition. For instance, you can join tables based on a specified range of values or a logical expression:

SELECT * 
FROM world.City 
JOIN world.Country ON (City.CountryCode = Country.Code)
WHERE City.Population > 1000000

USING

USING is a simplified syntax specifically designed for cases where the tables to be joined share an exact column name. Instead of specifying the column name in the ON clause, you simply use the USING keyword followed by the shared column name:

SELECT ... 
FROM film 
JOIN film_actor USING (film_id)
WHERE ...

Notable Differences

• Qualification of Joining Columns: With USING, you don't need to fully qualify the joining columns in the SELECT list. In contrast, ON requires you to prefix the column names with the table name.
• Duplicate Columns: When using ON, the joining column appears twice in the result set, while with USING, it appears only once.
• Flexibility: ON provides more flexibility in terms of the join condition, allowing you to specify more complex criteria.

Choosing the Right Option

Generally, USING is a more convenient option when the tables share an exact column and qualify both columns in the query. However, if you need to join tables on a condition or multiple columns, ON is the preferable choice.

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