How Can I Union Tables with Different Numbers of Columns?

Combining Tables with Different Column Counts

Database operations often involve merging data from multiple tables. However, these tables may not always have the same number of columns, posing a challenge for direct combination. This guide explains how to effectively unite tables with unequal column numbers.

Let's assume Table A has more columns than Table B. To successfully merge them, follow this process:

1. Identify Missing Columns: First, pinpoint the columns present in Table A that are absent in Table B.

2. Add NULL Placeholders: For each column missing from Table B, insert NULL values as placeholders in the corresponding rows. This signifies the absence of data in those specific columns.

3. Perform the Union: Use the UNION operator to combine the modified Table B with Table A. The resulting table will incorporate all columns from both original tables.

Here's an example SQL query demonstrating this method:

SELECT Col1, Col2, Col3, Col4, Col5
FROM TableA
UNION
SELECT Col1, Col2, Col3, NULL, NULL
FROM TableB;

By strategically incorporating NULL values, you can seamlessly combine tables with differing column structures, preserving all data without errors.

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