Tutorial Gateway

SQL UNION ALL

by

The SQL UNION ALL is used to combine two or more SELECT statements, and returns a single result set.

The Union ALL in Sql Server will select all the records (including duplicate records) from all queries.

The basic syntax behind the Union All in SQL Server is as shown below:

-- SQL Server UNION ALL Syntax
SELECT Column1, Column2 ......., ColumnN FROM Table1
UNION ALL
SELECT Column1, Column2 ......., ColumnN FROM Table2

The basic rules to use this Union ALL in SQL Server are:

  1. The number of columns, and its order must be same in all the queries.
  2. The column data types should compatible with each other.

In this article we will show you, How to write or use SQL Union All operator with example. For this SQL Query demonstration, We are going to use two tables (Employ, and Employees 2015) present in our [SQL Tutorial] Database.

From the below figure you can observe that, [Employ] table have ten records

SQL UNION ALL 5

And [Employees 2015] table have six records. Notice that, there is only two distinct records ((2, SQL, Server), and (2, Rob, Johnson)), and the remaining records are same.

SQL UNION Example 1

SQL Union All example

The following SQL Query will return all the records (including duplicate records) from Employ table, Employees 2015 table, and display the result

-- Example for SQL Server Union ALL
SELECT [ID]
      ,[FirstName]
      ,[LastName]
      ,[Occupation]
      ,[YearlyIncome]
      ,[Sales]
FROM [SQL Tutorial].[dbo].[Employ]
UNION ALL
SELECT [ID]
      ,[FirstName]
      ,[LastName]
      ,[Occupation]
      ,[YearlyIncome]
      ,[Sales]
FROM [SQL Tutorial].[dbo].[Employees 2015]

OUTPUT

SQL UNION ALL 1

SQL Union All along with Where

The following Query will display, How to use the UNION ALL operator along with the where clause, and ORDER BY Clause. In this example, we are combining two statement:

  • First result set – It will select all the records from Employ, whose Sales amount is greater than 500
  • Second result set – It will selects the records from Employees 2015 whose yearly income is greater than or equal to 70000
  • and the Union All operator will select all the records (including duplicates) from both the first result set, and the second result set.
-- Example for SQL Server Union ALL
SELECT [ID]
      ,[FirstName]
      ,[LastName]
      ,[Occupation]
      ,[YearlyIncome]
      ,[Sales]
FROM [SQL Tutorial].[dbo].[Employ]
WHERE [Sales] > 500
  UNION ALL
SELECT [ID]
      ,[FirstName]
      ,[LastName]
      ,[Occupation]
      ,[YearlyIncome]
      ,[Sales]
FROM [SQL Tutorial].[dbo].[Employees 2015]
WHERE [YearlyIncome] >= 70000
ORDER BY [ID]

OUTPUT

SQL UNION ALL 2

SQL Union All Errors

The following Query will display the common error that we face while working with the SQL Union All operator. For this, We are going to use two tables (Employee and Employees 2015) present in our [SQL Tutorial] Database.

From the below screenshot you can observe that, [Employee] table have 7 columns, and 14 rows.

SQL UNION ALL 7

Let us see what will happen, when we use Sql Server Union All operator on unequal length of columns.

-- SQL UNION ALL Example
SELECT [FirstName]
      ,[LastName]
      ,[Education]
      ,[Occupation]
      ,[YearlyIncome]
      ,[Sales]
      ,[HireDate]
  FROM [SQL Tutorial].[dbo].[Employee]
UNION 
SELECT [FirstName]
      ,[LastName]
      ,[Occupation]
      ,[YearlyIncome]
      ,[Sales]
  FROM [SQL Tutorial].[dbo].[Employees 2015]

OUTPUT

SQL UNION ALL 3

Hope you can read the above message. All queries combined using UNION operator must have an equal number of expressions in their target lists. Now, let us change the query to select equal number of columns

-- Example for SQL Server Union ALL
SELECT [FirstName]
      ,[LastName]
      ,[Occupation]
      ,[YearlyIncome], [Sales]
FROM [SQL Tutorial].[dbo].[Employee]
  UNION ALL
SELECT [FirstName]
      ,[LastName]
      ,[Occupation]
      ,[YearlyIncome], [Sales]
FROM [SQL Tutorial].[dbo].[Employees 2015]
ORDER BY [YearlyIncome] DESC

OUTPUT

SQL UNION ALL 4

From the above screenshot you can observe that, union all query is returning 20 records i.e., 14 from Employee table + 6 from Employees 2015 table.

Placed Under: SQL