The following example shows the incorrect and correct use of UNION in two SELECT statements in which a column is to be renamed in the output. The order of certain parameters used with the UNION clause is important. Using UNION of two SELECT statements with ORDER BY IF OBJECT_ID ('dbo.ProductResults', 'U') IS NOT NULLĬ. The Gloves table is created in the first SELECT statement. In the following example, the INTO clause in the second SELECT statement specifies that the table named ProductResults holds the final result set of the union of the selected columns of the ProductModel and Gloves tables. IF OBJECT_ID ('dbo.Gloves', 'U') IS NOT NULL In the following example, the result set includes the contents of the ProductModelID and Name columns of both the ProductModel and Gloves tables. If not specified, duplicate rows are removed. Incorporates all rows into the results, including duplicates. Specifies that multiple result sets are to be combined and returned as a single result set. If typed, they must be typed to the same XML schema collection. All columns must be either typed to an XML schema or untyped. For more information, see Precision, Scale, and Length (Transact-SQL).Ĭolumns of the xml data type must be equal. When the types are the same but differ in precision, scale, or length, the result is based on the same rules for combining expressions. When data types differ, the resulting data type is determined based on the rules for data type precedence. The definitions of the columns that are part of a UNION operation don't have to be the same, but they must be compatible through implicit conversion. Is a query specification or query expression that returns data to be combined with the data from another query specification or query expression. To view Transact-SQL syntax for SQL Server 2014 and earlier, see Previous versions documentation. The number and the order of the columns must be the same in all queries. The following are basic rules for combining the result sets of two queries by using UNION: A JOIN compares columns from two tables, to create result rows composed of columns from two tables.But a UNION does not create individual rows from columns gathered from two tables. A UNION concatenates result sets from two queries.You control whether the result set includes duplicate rows:Ī UNION operation is different from a JOIN: Concatenates the results of two queries into a single result set.
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