Execute Dynamic SQL commands in SQL Server

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In some applications having hard-coded SQL statements is not appealing, because of the dynamic nature of the queries being issued against the database server. Because of this sometimes there is a need to dynamically create a SQL statement on the fly and then run that command. This can be done quite simply from the application perspective where the statement is built on the fly whether you are using ASP.NET , ColdFusion or any other programming language. But how do you do this from within a SQL Server stored procedure? SQL Server offers a few ways of running a dynamically built SQL statement. These ways are: Writing a query with parameters Using EXEC Using sp_executesql Writing a query with parameters This first approach is pretty straightforward if you only need to pass parameters into the WHERE clause of your SQL statement. Let’s say we need to find all records from the Customers table where City = ‘London’. This can be done easily as the following example shows. ...
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SQL SubSelect-SubQueries

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A sub query or sub select is a select statement that returns a single value 
output result and it can be nested inside other subquery or any SELECT, INSERT,
DELETE OR UPDATE statement.

Example:
USE NORTHWIND

SELECT P.PRODUCTNAME,
(SELECT CATEGORYNAME FROM CATEGORIES WHERE CATEGORYID = P.CATEGORYID)
FROM PRODUCTS P

Subquery used in the above example returns the category name of each product
in every tuple.



Example:

SELECT P.PRODUCTNAME, P.UNITPRICE, P.CATEGORYID
FROM
PRODUCTS P
WHERE
P.PRODUCTID = (SELECT PRODUCTID FROM PRODUCTS WHERE PRODUCTNAME='VEGIE-SPREAD')

Here subquery returns product id as single value to the main SQL query.



Example:

SELECT C.CATEGORYNAME,

(SELECT TOP 1 P.PRODUCTNAME FROM PRODUCTS P WHERE P.CATEGORYID=C.CATEGORYID ORDER BY P.UNITPRICE DESC),

(SELECT TOP 1 P.UNITPRICE FROM PRODUCTS P WHERE P.CATEGORYID=C.CATEGORYID ORDER BY P.UNITPRICE DESC),

(SELECT MAX(P.UNITPRICE) FROM PRODUCTS P WHERE P.CATEGORYID=C.CATEGORYID)
/*TO VERIFY THE RESULT*/

FROM CATEGORIES C

Above example returns the maximum unit price of product, product name and category name.

Comments

Unknown said…
Nice post very helpful

dbakings
July 2, 2013 at 6:03 AM
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