Combined tables with different columns
]Can encounter challenges when trying to merge database tables with different columns. A straightforward way is to append null values to missing columns in a table with fewer columns.
For example, consider two tables, Table A and Table B, where Table A has more columns than Table B. To merge these tables and also process the missing columns in Table B, follow these steps:
The following SQL query demonstrates this process:
SELECT Col1, Col2, Col3, Col4, Col5
FROM Table1
UNION
SELECT Col1, Col2, Col3, NULL AS Col4, NULL AS Col5
FROM Table2;
In this query, "Col4" and "Col5" are missing columns in Table B, filled with null values in the UNION clause. Therefore, the UNION operation seamlessly merges the two tables and leaves the missing column values as nulls.
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