![]() ![]() We have seen that UNION and UNION ALL are useful to concatenate data sets and to manage whether or not we retain duplicates. This will result in an error being returned. While we have the correct number of columns, they are now queried in the wrong order in the second SELECT statement and thus the data types also do not match up. The next 2 examples shows that we would return results whether we used UNION or UNION ALL since all required criteria are met. The columns retrieved must be of similar data types.The columns retrieved must be in the same order in each SELECT statement.There must be the same number of columns retrieved in each SELECT statement to be combined.UNION or UNION ALL have the same basic requirements of the data being combined: *Note: In both of these examples, the field names from the first SELECT statement are retained and used as the field names in the result set. If we were to now perform the UNION ALL on the same data set, the query would skip the deduplication step and return the results shown. UNION first performs a sorting operation and eliminates of the records that are duplicated across all columns before finally returning the combined data set. UNION ALL keeps all of the records from each of the original data sets, UNION removes any duplicate records. UNION ALL: keeps all records, including duplicates.The main difference between UNION and UNION ALL is that: This allows us to write multiple SELECT statements, retrieve the desired results, then combine them together into a final, unified set. UNION and UNION ALL are SQL operators used to concatenate 2 or more result sets. You also learned the differences between UNION and UNION ALL operators.What is the difference between UNION and UNION ALL In this tutorial, you have learned how to use SQLite UNION operator to combine rows from result sets into a single result set. ORDER BY FirstName, LastName Code language: SQL (Structured Query Language) ( sql ) UNION SELECT FirstName, LastName, 'Customer' FROM customers SELECT FirstName, LastName, 'Employee' AS Type FROM employees In addition, it uses the ORDER BY clause to sort the name list by first name and last name. This example uses the UNION operator to combine the names of the employees and customers into a single list. Here is the output: 2) SQLite UNION with ORDER BY example UNION SELECT FirstName, LastName, 'Customer' FROM customers Ĭode language: SQL (Structured Query Language) ( sql ) This statement uses the UNION operator to combine names of employees and customers into a single list: SELECT FirstName, LastName, 'Employee' AS Type FROM employees Let’s take some examples of using the UNION operator. The following picture illustrates the UNION ALL operation of the result sets of t1 and t2 tables: SQLite UNION examples The following statement combines the result sets of t1 and t2 table using the UNION ALL operator: SELECT v1 The following picture illustrates the UNION operation of t1 and t2 tables: The following statement combines the result sets of the t1 and t2 table using the UNION operator: SELECT v1įROM t2 Code language: SQL (Structured Query Language) ( sql ) VALUES( 2),( 3),( 4) Code language: SQL (Structured Query Language) ( sql ) Suppose we have two tables t1 and t2 with the following structures: CREATE TABLE t1( Note that the difference between UNION and JOIN e.g., INNER JOIN or LEFT JOIN is that the JOIN clause combines columns from multiple related tables, while UNION combines rows from multiple similar tables. ![]() The ORDER BY clause is applied to the combined result set, not within the individual result set. ![]()
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