How Can I Use UNION to Combine Tables with Different Numbers of Columns?

Combining Database Tables with Varying Column Counts

Database tables frequently have different numbers of columns. This presents a challenge when using UNION to combine them, as mismatched column numbers can cause errors. The solution involves strategically adding NULL values to the smaller table.

When combining tables with unequal column counts, we can supplement the table with fewer columns by adding extra columns filled with NULL values. This ensures all tables have the same number of columns, allowing a successful UNION operation. These NULL values represent the absence of data in those columns for the smaller table.

Here's an example:

<code class="language-sql">SELECT Col1, Col2, Col3, Col4, Col5 FROM Table1
UNION
SELECT Col1, Col2, Col3, NULL AS Col4, NULL AS Col5 FROM Table2</code>

This example assumes Table1 has five columns and Table2 has three. By appending two NULL columns to the SELECT statement for Table2, the UNION operation can proceed without issues, effectively combining the tables.

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