How to Efficiently Select Data from Multiple MySQL Tables with Identical Structures?

MySQL: Selecting Data from Multiple Tables with Identical Structures but Distinct Data

When managing large datasets, it's often necessary to store data in multiple tables with identical schema for localization or partitioning purposes. However, extracting data from multiple tables while maintaining a specific sort order can present challenges.

Problem: Ambiguous Column Error in WHERE Clause

Consider the following MySQL statement:

SELECT * from us_music, de_music where `genre` = 'punk'

This query attempts to join data from two tables, us_music and de_music, based on the genre column, which exists in both tables. However, MySQL returns the following error:

#1052 - Column 'genre' in where clause is ambiguous

Solution: Using the UNION Clause

To resolve the ambiguity, you can use the UNION clause. The UNION clause combines the results of multiple SELECT statements into a single result set. Here's how to use it in this case:

(SELECT * from us_music where `genre` = 'punk')
UNION
(SELECT * from de_music where `genre` = 'punk')

This query first selects data from us_music where the genre equals 'punk', then it performs the same operation on de_music. The results of both SELECT statements are then combined into a single result set.

Sorting the Combined Results

Once the data is combined, you can specify a sort order by adding an ORDER BY clause after the UNION statement:

(SELECT * from us_music where `genre` = 'punk')
UNION
(SELECT * from de_music where `genre` = 'punk')
ORDER BY `band_name`

This query will combine the data from both tables and sort the results based on the band_name column.

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