How Can I Identify Discrepancies Between Two SQL Tables?

Comparing SQL Tables to Find Data Differences

Ensuring data consistency across two SQL Server tables requires identifying rows unique to each. This highlights discrepancies and missing data. Here's how to accomplish this using SQL queries:

One approach uses the EXCEPT operator:

(SELECT * FROM table1 EXCEPT SELECT * FROM table2)

This query shows rows present in table1 but absent from table2. To find rows unique to table2, simply swap the table names:

(SELECT * FROM table2 EXCEPT SELECT * FROM table1)

For a combined view of all unique rows across both tables, utilize UNION ALL:

<code class="language-sql">(SELECT * FROM table1 EXCEPT SELECT * FROM table2)
UNION ALL
(SELECT * FROM table2 EXCEPT SELECT * FROM table1)</code>

If your tables lack NULL values, a more efficient method employs NOT EXISTS. This example retrieves rows from table1 not found in table2:

<code class="language-sql">SELECT *
FROM table1
WHERE NOT EXISTS (
    SELECT *
    FROM table2
    WHERE table2.column1 = table1.column1
)</code>

Remember to replace table1, table2, and column1 with your actual table and column names. Choose the method best suited to your data and needs.

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