How can tables with differing columns be combined together through union?

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To combine tables with differing columns through union, the columns from both tables must be made compatible. This can be done by adding NULL values or default values for missing columns in one table so that they match the columns in the other table.

For example, suppose we have two tables:

Table 1: - Name - Age

Table 2: - Name - Gender - Occupation

To combine these tables, we can add a default value for Occupation in Table 1, so that the number of columns in both tables match:

SELECT Name, Age, NULL AS Gender, 'unemployed' AS Occupation FROM Table 1 UNION SELECT Name, NULL AS Age, Gender, Occupation FROM Table 2

This will create a new table with all the columns from both tables, and default values for missing columns as needed.