JOIN and UNION in database operations
In database operations, the two operators JOIN and UNION play completely different roles. Understanding their differences is critical for effective data manipulation.
JOIN operator
The JOIN operator combines rows from two or more tables based on common or related columns. It forms the Cartesian product of individual table rows and filters out the appropriate subset based on the specified join conditions. This allows cross-referencing data between tables and extracting insights from their relationships.
Example:
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This query retrieves all columns in rows in table1 and table2 where all id columns match.
UNION operator
In contrast, the UNION operator appends the result rows of one query to another query. It combines the results of multiple queries into a single rowset without establishing any relationship between them. The results of the UNION operator do not exhibit any cross-join properties.
Example:
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This query will produce a table containing all rows from table1 and table2, arranged one after the other, regardless of any specific join conditions.
Main differences
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