How Can I Union Tables with Different Numbers of Columns Without Data Loss?

Merging Tables with Unequal Column Counts

Combining data from tables with different numbers of columns requires a strategy to prevent data loss. This example shows how to merge Table A (more columns) and Table B (fewer columns) while retaining all data.

The solution involves using NULL values as placeholders for the columns missing in the smaller table. This maintains a consistent column count in the combined result.

Here's the SQL query:

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

This query unites data from both tables. NULL is explicitly assigned to Col4 and Col5 in the TableB selection, matching the column structure of TableA. This preserves all columns from both tables, filling gaps with NULL where necessary. Using UNION ALL instead of UNION will keep duplicate rows if they exist in both tables.

This method allows for efficient merging of tables with differing column structures, facilitating seamless data analysis and manipulation across multiple data sources.

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