SQL UNION ALL Last Updated : 06 Dec, 2024 Comments Improve Suggest changes Like Article Like Report UNION ALL Operator is used to combine the results of two or more SELECT statements into a single result set. Unlike the UNION operator, which eliminates duplicate records and UNION ALL includes all duplicates. This makes UNION ALL it faster and more efficient when we don't need to remove duplicates.In this article, we will learn the SQL UNION ALL operator, how it compares with UNION, and practical examples to demonstrate its usage in real applications.SQL UNION ALL OperatorThe SQL UNION ALL command combines the result of two or more SELECT statements in SQL. For performing the UNION ALL operation, it is necessary that both the SELECT statements should have an equal number of columns/fields, otherwise, the resulting expression will result in an error.Syntax:The syntax for the SQL UNION ALL operation is: SELECT columns FROM table1 UNION ALL SELECT columns FROM table2;Examples of SQL UNION ALL Let's look at some examples of the UNION ALL command in SQL to understand its working. First, let's create a demo SQL database and tables on which UNION ALL will be performed.Demo SQL DatabaseIn this tutorial on the UNION ALL operator, we will use the following table in examples.STUDENTS table:ROLL_NONAMEDOBAGE1DEV SHARMA2001-08-16172AMAN VERMA2002-01-04163KRISH VATSA2000-11-2918TRIP_DETAIL Table:ROLL_NONAMEDOBAGE1DEV SHARMA2001-08-16172AMAN VERMA2002-01-04163KRISH VATSA2000-11-29184VARUN GOYAL2003-09-2115Example 1: Single Field With Same NameWe want to combine the names from both the STUDENTS and TRIP_DETAIL tables, including all names, even if there are duplicates.SELECT NAME FROM STUDENTS UNION ALL SELECT NAME FROM TRIP_DETAIL;Output:NAMEDEV SHARMAAMAN VERMAKRISH VATSADEV SHARMAAMAN VERMAKRISH VATSAVARUN GOYALExplanation: The UNION ALL operator combines all rows from the NAME column in both tables. It includes all names, including duplicates. In this case, "DEV SHARMA", "AMAN VERMA", and "KRISH VATSA" appear twice because they exist in both tables.Example 2: Different Field NamesSuppose We want to combine the ROLL_NO from both tables and align the column names for consistency.Query:SELECT ROLL_NO AS Identifier FROM STUDENTS UNION ALL SELECT ROLL_NO AS Identifier FROM TRIP_DETAIL;Output:Identifier1231234Explanation: Here, ROLL_NO from both tables is selected and aliased as Identifier. The UNION ALL operator combines all roll numbers from both tables, including duplicates. Each ROLL_NO from STUDENTS appears twice because it also exists in TRIP_DETAIL.Important Points About SQL UNION All UNION ALL command helps us to combine results of two or more SELECT statements from different tables. The UNION ALL command includes the duplicate records from the SELECT statements whereas the UNION command does not include duplicate records otherwise both the commands are same. For performing the UNION ALL operation, it is necessary that both the SELECT statements should have equal number of columns otherwise the resulting expression will result in an error.SQL UNION All vs UNIONHere is the comparison between UNION ALL and UNION Operator:FeatureUNION ALLUNIONDuplicate RecordsIncludes all duplicatesRemoves duplicate recordsPerformanceFaster, as it doesn't check for duplicatesSlower, as it needs to eliminate duplicatesUse CaseWhen duplicates are acceptable or neededWhen duplicates need to be removedSyntaxSELECT columns FROM table1 UNION ALL SELECT columns FROM table2;SELECT columns FROM table1 UNION SELECT columns FROM table2;Memory UsageGenerally lower, since no extra processing for duplicatesHigher, due to additional steps for duplicate removalResult SetCombined rows from all SELECT statements, including duplicatesCombined rows from all SELECT statements, without duplicatesApplicabilityUseful for large datasets where performance is critical and duplicates are acceptableUseful when data integrity requires unique records in the result setConclusionThe UNION ALL operator is a powerful tool for combining results from multiple queries while preserving all rows, including duplicates. It is particularly useful when you need to aggregate data from similar sources or when duplicates are not a concern. The examples provided illustrate how UNION ALL works with columns of the same and different names.Can UNION ALL be used with different data types?No, the columns being combined with UNION ALL must have compatible data types. If they differ, you may need to cast or convert the data types to make them compatible.How does UNION ALL handle NULL values?UNION ALL will include NULL values in the result set. If NULL values exist in the result sets of the queries being combined, they will appear in the final result set.Can UNION ALL be used with more than two tables?Yes, UNION ALL can combine results from more than two SELECT queries. You can chain multiple SELECT queries with UNION ALL to aggregate data from several sources. 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It is different from a zero value or blank space, and it indicates that the value is unknown.In this article, we will lea 4 min read SQL UNION OperatorThe SQL UNION operator is used to combine the result sets of two or more SELECT queries into a single result set. It is a powerful tool in SQL that helps aggregate data from multiple tables, especially when the tables have similar structures.In this guide, we'll explore the SQL UNION operator, how i 4 min read SQL UNION ALLUNION ALL Operator is used to combine the results of two or more SELECT statements into a single result set. Unlike the UNION operator, which eliminates duplicate records and UNION ALL includes all duplicates. This makes UNION ALL it faster and more efficient when we don't need to remove duplicates. 4 min read SQL | Except ClauseThe SQL EXCEPT operator is used to return the rows from the first SELECT statement that are not present in the second SELECT statement. This operator is conceptually similar to the subtract operator in relational algebra. It is particularly useful for excluding specific data from your result set.In 4 min read SQL BETWEEN OperatorThe BETWEEN operator in SQL is used to filter records within a specific range. Whether applied to numeric, text, or date columns it simplifies the process of retrieving data that falls within a particular boundary. In this article, we will explore the SQL BETWEEN operator with examples.SQL BETWEEN O 3 min read SQL | ALL and ANYIn SQL, the ALL and ANY operators are logical operators used to compare a value with a set of values returned by a subquery. These operators provide powerful ways to filter results based on a range of conditions. In this article, we will explore ALL and ANY in SQL, their differences, and how to use 4 min read SQL | ALL and ANYIn SQL, the ALL and ANY operators are logical operators used to compare a value with a set of values returned by a subquery. 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These functions allow you to gather valuable insights from your database, such as calculating totals, and averages, and counting specific rows. In this article, we will expla 3 min read SQL COUNT(), AVG() and SUM() FunctionSQL aggregate functions, such as COUNT(), AVG(), and SUM(), are essential tools for performing mathematical analysis on data. These functions allow you to gather valuable insights from your database, such as calculating totals, and averages, and counting specific rows. In this article, we will expla 3 min read SQL MIN() and MAX() FunctionsThe SQL MIN() and MAX() functions are essential aggregate functions in SQL used for data analysis. They allow you to extract the minimum and maximum values from a specified column, respectively, making them invaluable when working with numerical, string, or date-based data. 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