EXCEPT and INTERSECT (Transact-SQL)
Returns distinct values by comparing the results of two queries.
EXCEPT returns any distinct values from the left query that are not also found on the right query.
INTERSECT returns any distinct values that are returned by both the query on the left and right sides of the INTERSECT operand.
The basic rules for combining the result sets of two queries that use EXCEPT or INTERSECT are the following:
The number and the order of the columns must be the same in all queries.
The data types must be compatible.
When the data types of comparable columns that are returned by the queries to the left and right of the EXCEPT or INTERSECT operands are character data types with different collations, the required comparison is performed according to the rules of collation precedence. If this conversion cannot be performed, the SQL Server Database Engine returns an error.
When you compare rows for determining distinct values, two NULL values are considered equal.
The column names of the result set that are returned by EXCEPT or INTERSECT are the same names as those returned by the query on the left side of the operand.
Column names or aliases in ORDER BY clauses must reference column names returned by the left-side query.
The nullability of any column in the result set returned by EXCEPT or INTERSECT is the same as the nullability of the corresponding column that is returned by the query on the left side of the operand.
If EXCEPT or INTERSECT is used together with other operators in an expression, it is evaluated in the context of the following precedence:
Expressions in parentheses
The INTERSECT operand
EXCEPT and UNION evaluated from left to right based on their position in the expression
If EXCEPT or INTERSECT is used to compare more than two sets of queries, data type conversion is determined by comparing two queries at a time, and following the previously mentioned rules of expression evaluation.
EXCEPT and INTERSECT cannot be used in distributed partitioned view definitions, query notifications, or together with COMPUTE and COMPUTE BY clauses.
EXCEPT and INTERSECT may be used in distributed queries, but are only executed on the local server and not pushed to the linked server. Therefore, using EXCEPT and INTERSECT in distributed queries may affect performance.
Fast forward-only and static cursors are fully supported in the result set when they are used with an EXCEPT or INTERSECT operation. If a keyset-driven or dynamic cursor is used together with an EXCEPT or INTERSECT operation, the cursor of the result set of the operation is converted to a static cursor.
When an EXCEPT operation is displayed by using the Graphical Showplan feature in SQL Server Management Studio, the operation appears as a left anti semi join, and an INTERSECT operation appears as a left semi join.
The following examples show using the INTERSECT and EXCEPT operands. The first query returns all values from the Production.Product table for comparison to the results with INTERSECT and EXCEPT.
USE AdventureWorks2008R2; GO SELECT ProductID FROM Production.Product ; --Result: 504 Rows
The following query returns any distinct values that are returned by both the query on the left and right sides of the INTERSECT operand.
USE AdventureWorks2008R2; GO SELECT ProductID FROM Production.Product INTERSECT SELECT ProductID FROM Production.WorkOrder ; --Result: 238 Rows (products that have work orders)
The following query returns any distinct values from the query to the left of the EXCEPT operand that are not also found on the right query.
USE AdventureWorks2008R2; GO SELECT ProductID FROM Production.Product EXCEPT SELECT ProductID FROM Production.WorkOrder ; --Result: 266 Rows (products without work orders)
The following query returns any distinct values from the query to the left of the EXCEPT operand that are not also found on the right query. The tables are reversed from the previous example.
USE AdventureWorks2008R2; GO SELECT ProductID FROM Production.WorkOrder EXCEPT SELECT ProductID FROM Production.Product ; --Result: 0 Rows (work orders without products)