How to compare data in 2 tables in SQL?

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Khushi Singh · Answer

The methods for data comparison between two SQL tables vary according to the desired outcome. The comparison process for the two tables includes the detection of various discrepancies and coincidences and the identification of absent and changed records.

Matching records between the two tables can be found through an INNER JOIN while using LEFT JOIN or RIGHT JOIN allows users to identify records located in one table that are not present in the other table.

EXCEPT combined with UNION makes another available method for data comparison. EXCEPT enables the detection of data items present in the first table without appearing in the second table as well as in the opposite direction. The results from the UNION ALL operation produce combined output while showing what data points differ between both sets of data.

The NOT EXISTS technique serves as an efficient tool that detects missing values from a unique key to identify records present in one table but absent in the other.

The FULL OUTER JOIN method provides a solution for comparing data between tables while showing variations in column contents. With this method, you can detect every row that exists in one table while missing from the other table and all cases of column value mismatch.

Start the comparison process only when both tables share an identical key that serves as an accurate reference. The key column indexing operation strengthens database performance based on the current database dimensions.

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How to compare data in 2 tables in SQL?

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