Introduction
APPLY operator is a new feature in SQL Server 2005 and TOP has some new enhancements in SQL 2005. We will discuss these two operators in this article.
APPLY Operators
APPLY operator is a new feature in SQL Server 2005 used in the FROM
clause of a query. It allows you to call a function-returning TABLE
for each row of your outer TABLE
. We can pass outer table's columns as function arguments.
It has two options:
- CROSS APPLY, and
- OUTER APPLY
CROSS APPLY will not return the outer tables row if function table has no row corresponding to it, whereas OUTER APPLY returns NULL
values instead of function columns.
The below query returns all the records of the customer table matching with cust.CustomerID
. To execute the code below, you need to have two database tables listed below with some data in it.
CREATE TABLE Customer(CustomerID INT, CustName VARCHAR(max))
CREATE TABLE Orders(OrderID int IDENTITY(1,1) NOT NULL,CustomerID int,_
SalesPersonID int,OrderDate datetime,Amount int)
Using the Code
CREATE FUNCTION fnGetCustomerInfo (@custid int)
RETURNS TABLE
AS
RETURN
(
SELECT *
FROM Orders
WHERE customerid=@custid
)
SELECT * FROM Customer cust
CROSS APPLY
fnGetCustomerInfo(cust.CustomerID)
ORDER BY cust.CustName
TOP Operator
In SQL 2005, TOP is used to restrict the number of rows returned as a number or percentage in SELECT
, UPDATE
, DELETE
or INSERT
statements. Earlier, this was possible only with SELECT
query. This enhanced feature replaces SET ROW COUNT
which had performance issues.
Syntax: TOP <literal> or <expression> [PERCENT]
Note: Expression should be of bigint
for literal option and float
for expression option.
SELECT TOP 10 * FROM Orders
SELECT TOP (SELECT count(*) FROM Customer) * FROM Orders
DECLARE @NOROWS AS FLOAT
SET @NOROWS = 70
SELECT TOP (@NOROWS) PERCENT * FROM Orders
Points of Interest
For more articles on SQL Server, visit www.geocities.com/ProgrammersVision.
History
- 4th May, 2007: Initial post