rdlc report print barcode 4: Transact-SQL Primer in Visual Studio .NET

Encoder QR in Visual Studio .NET 4: Transact-SQL Primer

4: Transact-SQL Primer
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Lists of Values (IN and NOT IN)
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Using a list of values, we can greatly simplify complex OR statements For example, say you are asked to retrieve a listing of contacts with first names of Sandy, Jay, Carla, or Ronald Using the OR statement, your query may look like this:
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SELECT ContactID, Title, FirstName, LastName, EmailAddress FROM PersonContact WHERE FirstName = 'Sandy' OR FirstName = 'Jay' OR FirstName = 'Carla' OR FirstName = 'Ronald'
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Instead, we can simplify this query with the IN operator by using the following query:
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SELECT ContactID, Title, FirstName, LastName, EmailAddress FROM PersonContact WHERE FirstName IN ('Sandy', 'Jay', 'Carla','Ronald')
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The query optimizer would handle both statements (using OR or using IN) the same way However, for a DBA analyzing queries, the query using IN is much easier to read
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Unknown Values (IS NULL and IS NOT NULL)
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Checking for NULL values is sometimes needed For example, you might be asked to provide a listing of only contacts that don t have a fax number, or only contacts that do have fax numbers A common mistake when checking for null values is to try to use a comparison operator such as = The = comparison operator can be used to check for known values, but the value of NULL is unknown In the following script, we check for any contacts that don t have middle names listed (or in other words, have a value of NULL for their middle name):
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SELECT ContactID, Title, FirstName, MiddleName LastName, EmailAddress FROM PersonContact Where MiddleName IS Null
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EXAM TIP Remember that we must use the IS NULL or IS NOT NULL function to check for NULL values We cannot use a comparison to an empty string to determine if a value is NULL
Exists in Subquery (EXISTS and NOT EXISTS)
We can use subqueries (a query within a query) with the EXISTS or NOT EXISTS clause to retrieve data based on the existence of the data within a subquery This sounds more complicated than it is In AdventureWorks, we have the PersonContact table, which lists all types of contacts (employees, customers, and vendors) Which of these contacts are employees Only the ones that also exist in the Employees table For example, let s say you were asked to pull a listing (first name, last name, and email address) of employees One way to do it is with an EXISTS clause The HumanResourcesEmployee table lists all the employees and has a ContactsID column used as an FK to the PersonContactContactsID PK The following query will
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pull data out of the PersonContact table as long as the ContactID exists in the HumanResourcesEmployee table:
SELECT FirstName, LastName FROM PersonContact WHERE EXISTS (SELECT * FROM HumanResourcesEmployee WHERE PersonContactContactID = HumanResourcesEmployeeContactID)
Later, we ll see how to do this with JOINs Exercise 43: Using the WHERE Clause to Filter Data 1 Open SSMS and create a New Query window 2 Retrieve all the information on all the products in the AdventureWorks database by entering the following script:
USE AdventureWorks SELECT * FROM ProductionProduct
3 Limit the columns displayed to just the product name, the product number, the cost, and the list price by using the following script:
SELECT Name, ProductNumber, StandardCost, ListPrice FROM ProductionProduct
4 Filter the result set by only listing products that have a cost greater than 0:
USE AdventureWorks SELECT Name, ProductNumber, StandardCost, ListPrice FROM ProductionProduct WHERE StandardCost > 0
5 Find any parts that have a part number starting with CN:
SELECT Name, ProductNumber, StandardCost, ListPrice FROM ProductionProduct WHERE ProductNumber Like 'CN%'
6 Find any parts with a Standard Cost greater than $0 and less than $100:
SELECT Name, ProductNumber, StandardCost, ListPrice FROM ProductionProduct WHERE StandardCost > 0 AND StandardCost < 100
This script will return 111 rows if AdventureWorks hasn t been modified 7 Retrieve a listing of parts with a cost BETWEEN $0 and $100:
SELECT Name, ProductNumber, StandardCost, ListPrice FROM ProductionProduct WHERE StandardCost BETWEEN 000 and 100
Notice this will return 311 rows because it is inclusive of $0 and $100 8 Retrieve a listing of parts where the part number begins with the letter A, B, or C Note that this query could be done in different ways, but the following script demonstrates use of the EXISTS clause:
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