How do you connect multiple tables using a union in SQL?

In SQL, the UNION operator is used to combine the results of queries from multiple tables into one result set. It is used to merge the results of two or more SELECT statements while removing duplicate rows.

Here is the method for connecting multiple tables using UNION.

1. Basic syntax: Retrieve column1 and column2 from table1 and table2 and combine the results using a UNION operator.
2. The two query statements that need to be merged are SELECT column1, column2 FROM table1 and SELECT column1, column2 FROM table2.
3. Note: The UNION operator automatically eliminates duplicates, if you do not want to eliminate duplicates, you can use UNION ALL.
4. Combine multiple tables: You can merge the results of multiple queries into one result set by using the UNION operator multiple times.
5. Combine the columns column1 and column2 from tables table1, table2, and table3.
6. Please be aware:
7. Each SELECT statement must return the same number of columns and the corresponding column types must be compatible.
8. The column names in the result set are determined by the column names in the first SELECT statement.
9. The UNION operator by default eliminates duplicate rows, but if you need to keep duplicate rows you can use UNION ALL.

In conclusion, the UNION operator can combine the query results of multiple tables into one result set, making it easier to perform cross-table queries and analysis.