Keywords UNION and UNION ALL are used for uniting results from two or more SQL queries into a single table. Note that each result of an SQL query must have the same number of columns, and the columns must contain similar type of data. Besides that, columns must be ordered similarly. UNION and UNION ALL functions differ from each other by the fact that the first function deletes repeating rows from the resulting table. The syntax is rather simple:
SELECT columns FROM table1 UNION SELECT columns FROM table2 UNION SELECT columns FROM table3
Try to unite 'orders' and 'orders_2013' tables
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