Best PracticesTransact-SQL

Transact-SQL Syntax Elements

Batch Directives Comments Identifiers Types of Data Variables

System Functions Operators Expressions Control-of-Flow

Language Elements Reserved Keywords

Batch Directives

GO Delineates batches of Transact-SQL statements to tools

and utilities Is not an actual Transact-SQL statement

EXEC Executes a user-defined function, system procedure,

user-defined stored procedure, or an extended stored procedure

Controls the execution of a character string within a Transact-SQL batch

Comments

In-line Comments

Block Comments

SELECT productname, (unitsinstock - unitsonorder) -- Calculates inventory, supplierIDFROM productsGO

/* This code retrieves all rows of the products table and displays the unit price, the unit price increased by 10 percent, and the name of the product. */USE northwindSELECT unitprice, (unitprice * 1.1), productname FROM productsGO

Example 3

Example 1

Identifiers

Standard Identifiers First character must be alphabetic Other characters can include letters, numerals, or

symbols

Identifiers starting with symbols have special uses Delimited Identifiers

Use when names contain embedded spaces Use when reserved words are portions of names Enclose in brackets ([ ]) or quotation marks (" ")

Naming Guidelines for Identifiers

Keep Names Short Use Meaningful Names Where Possible Use Clear and Simple Naming Conventions Use an Identifier That Distinguishes Types of Object

Views Stored procedures

Keep Object Names and User Names Unique Sales table and sales role

Types of Data

Numbers Dates Characters Binary Unique Identifiers (GUID)

SQL Variants Image and Text Table Cursor User-defined

Variables

User-defined with DECLARE @ Statement Assigned Values with SET or SELECT @ Statement Variables Have Local Scope

USE northwindDECLARE @EmpID varchar(11) ,@vlName char(20)SET @vlname = 'Dodsworth'SELECT @EmpID = employeeid FROM employees WHERE LastName = @vlnameSELECT @EmpID AS EmployeeID GO

System Functions

Aggregate Functions

Scalar Functions

Rowset FunctionsSELECT * FROM OPENQUERY (OracleSvr, 'SELECT name, id FROM owner.titles')

USE northwindSELECT AVG (unitprice) AS AvgPrice FROM productsGO

USE northwindSELECT DB_NAME() AS 'database‘GO

System Function Examples

SELECT 'ANSI:', CONVERT(varchar(30), GETDATE(), 102) AS StyleUNIONSELECT 'Japanese:', CONVERT(varchar(30), GETDATE(), 111)UNIONSELECT 'European:', CONVERT(varchar(30), GETDATE(), 113)GO

Result

StyleStyleANSI:Japanese:European:

1998.03.191998/03/1919 Mar 1998 16:34:40:616

Example 1

Operators

Types of Operators Arithmetic

Comparison

String concatenation

Logical

Operator Precedence Levels

Expressions

Combination of Symbols and Operators Evaluation to Single Scalar Value Result Data Type Dependent on the Elements

Within the Expression

USE northwindSELECT OrderID, ProductID ,(UnitPrice * Quantity) as ExtendedAmount FROM [Order Details] WHERE (UnitPrice * Quantity) > 10000GO

Control-of-Flow Language Elements

Statement Level BEGIN … END block

IF … ELSE block

WHILE constructs

Row Level CASE function

DECLARE @n tinyintSET @n = 5IF (@n BETWEEN 4 and 6) BEGIN WHILE (@n > 0) BEGIN SELECT @n AS 'Number' ,CASE WHEN (@n % 2) = 1 THEN 'EVEN' ELSE 'ODD' END AS 'Type' SET @n = @n - 1 END ENDELSE PRINT 'NO ANALYSIS‘GO

Example 2

Reserved Keywords

Identifier Names That Have Special Meaning Transact-SQL keywords

ANSI SQL-92 keywords

ODBC reserved keywords

Do Not Use Reserved Keywords for Identifier Names

Retrieving Data by Using the SELECT Statement

Using the SELECT Statement Specifying Columns Using the WHERE Clause to Specify Rows

SELECT [ALL | DISTINCT] <select_list> FROM {<table_source>} [,…n] WHERE <search_condition>

Partial Syntax

Using the SELECT Statement

Select List Specifies the Columns WHERE Clause Specifies the Condition Restricting the

Query FROM Clause Specifies the Table

Specifying Columns

employeeidemployeeid lastnamelastname firstnamefirstname titletitle1 Davolio Nancy Sales Representative2 Fuller Andrew Vice President, Sales3 Leverling Janet Sales Representative4 Peacock Margaret Sales Representative5 Buchanan Steven Sales Manager6 Suyama Michael Sales Representative7 King Robert Sales Representative8 Callahan Laura Inside Sales Coordinator9 Dodsworth Anne Sales Representative

USE northwindSELECT employeeid, lastname, firstname, titleFROM employeesGO

Using the WHERE Clause to Specify Rows

employeeidemployeeid lastnamelastname firstnamefirstname titletitle5 Buchanan Steven Sales Manager

USE northwindSELECT employeeid, lastname, firstname, titleFROM employeesWHERE employeeid = 5GO

Filtering Data

Using Comparison Operators Using String Comparisons Using Logical Operators Retrieving a Range of Values Using a List of Values as Search Criteria Retrieving Unknown Values

Using Comparison Operators

USE northwindSELECT lastname, cityFROM employeesWHERE country = 'USA'GO

lastnamelastname citycityDavolio SeattleFuller TacomaLeverling KirklandPeacock RedmondCallahan Seattle

Example 1

Using String Comparisons

USE northwindSELECT companynameFROM customersWHERE companyname LIKE '%Restaurant%'GO

companynamecompanynameGROSELLA-RestauranteLonesome Pine RestaurantTortuga Restaurante

Using Logical Operators

USE northwindSELECT productid, productname, supplierid, unitprice FROM products WHERE (productname LIKE 'T%' OR productid = 46) AND (unitprice > 16.00) GO

productidproductid productnameproductname supplieridsupplierid unitpriceunitprice14 Tofu 6 23.2529 Thüringer Rostbratwurst 12 123.7962 Tarte au sucre 29 49.3

Example 1

Retrieving a Range of Values

USE northwindSELECT productname, unitpriceFROM productsWHERE unitprice BETWEEN 10 AND 20GO

productnameproductname unitpriceunitpriceChai 18Chang 19Aniseed Syrup 10Genen Shouyu 15.5Pavlova 17.45Sir Rodney’s Scones 10… …

Example 1

USE northwindSELECT companyname, countryFROM suppliersWHERE country IN ('Japan', 'Italy')GO

Using a List of Values as Search Criteria

companynamecompanyname countrycountryTokyo Traders JapanMayumi’s JapanFormaggi Fortini s.r.l. ItalyPasta Buttini s.r.l. Italy

Example 1

Retrieving Unknown Values

USE northwindSELECT companyname, faxFROM suppliersWHERE fax IS NULLGO

companynamecompanyname faxfaxExotic Liquids NULLNew Orleans Cajun Delights NULLTokyo Traders NULLCooperativa de Quesos ‘Las Cabras’ NULL… …

Formatting Result Sets

Sorting Data Eliminating Duplicate Rows Changing Column Names Using Literals

Sorting Data

USE northwindSELECT productid, productname, categoryid, unitprice FROM products ORDER BY categoryid, unitprice DESCGO

productidproductid productnameproductname categoryidcategoryid unitpriceunitprice38 Cote de Blaye 1 263.500043 Ipoh Coffee 1 46.00002 Chang 1 19.0000… … … …63 Vegie-spread 2 43.90008 Northwoods Cranberry Sauce 2 40.000061 Sirop d'érable 2 28.5000… … … …

Example 1

Eliminating Duplicate Rows

USE northwindSELECT DISTINCT country FROM suppliers ORDER BY countryGO

countrycountryAustraliaBrazilCanadaDenmarkFinlandFranceGermanyItalyJapanNetherlandsNorwaySingaporeSpainSwedenUKUSA

Example 1

Changing Column Names

USE northwindSELECT firstname AS First, lastname AS Last

,employeeid AS 'Employee ID:' FROM employeesGO

FirstFirst LastLast Employee ID:Employee ID:Nancy Davolio 1Andrew Fuller 2Janet Leverling 3Margaret Peacock 4Steven Buchanan 5Michael Suyama 6Robert King 7Laura Callahan 8Anne Dodsworth 9

Using Literals

USE northwindSELECT firstname, lastname

,'Identification number:', employeeidFROM employeesGO

FirstFirst LastLast Employee ID:Employee ID:Nancy Davolio Identification Number: 1Andrew FullerJanet LeverlingMargaret PeacockSteven BuchananMichael SuyamaRobert KingLaura CallahanAnne Dodsworth

Identification Number: 2Identification Number: 3Identification Number: 4Identification Number: 5Identification Number: 6Identification Number: 7Identification Number: 8Identification Number: 9

How Queries Are Processed

Uncached Queries (Ad Hoc)

Cached Queries

ExecuteCompileOptimizeResolveParse

First Execution

ExecuteCompileOptimizeResolveParse

Subsequent Execution ExecuteProcedureCache

Performance Considerations

Not Search Conditions May Slow Data Retrieval LIKE Search Conditions Slow Data Retrieval Exact Matches or Ranges May Speed Data Retrieval ORDER BY Clause May Slow Data Retrieval

Listing the TOP n Values

Lists Only the First n Rows of a Result Set Specifies the Range of Values in the ORDER BY Clause Returns Ties if WITH TIES Is Used

USE northwindSELECT TOP 5 orderid, productid, quantity FROM [order details] ORDER BY quantity DESCGO

USE northwindSELECT TOP 5 WITH TIES orderid, productid, quantity FROM [order details] ORDER BY quantity DESCGO

Example 1

Example 2

Using Aggregate Functions

Aggregate functionAggregate function DescriptionDescriptionAVG Average of values in a numeric expression

COUNT Number of values in an expression

COUNT (*) Number of selected rows

MAX Highest value in the expression

MIN Lowest value in the expression

SUM Total values in a numeric expression

STDEV Statistical deviation of all values

STDEVP Statistical deviation for the population

VAR Statistical variance of all values

VARP Statistical variance of all values for the population

Using Aggregate Functions with Null Values

Most Aggregate Functions Ignore Null Values COUNT(*) Function Counts Rows with Null Values

USE northwindSELECT COUNT (*) FROM employeesGO

USE northwindSELECT COUNT(reportsto) FROM employeesGO

Example 1

Example 2

GROUP BY Fundamentals

Using the GROUP BY Clause Using the GROUP BY Clause with the HAVING Clause

Using the GROUP BY ClauseUSE northwindSELECT productid, orderid ,quantity FROM orderhistGO

USE northwindSELECT productid ,SUM(quantity) AS total_quantity FROM orderhist GROUP BY productidGO

productidproductid total_quantitytotal_quantity1 15

2 35

3 45

productidproductid orderidorderid quantityquantity1 1 5

1 1 10

2 1 10

2 2 25

3 1 15

3 2 30

productidproductid total_quantitytotal_quantity2 35

Only rows thatsatisfy the WHERE clause are grouped

USE northwindSELECT productid ,SUM(quantity) AS total_quantity FROM orderhist WHERE productid = 2 GROUP BY productidGO

Using the GROUP BY Clause with the HAVING Clause

USE northwindSELECT productid, orderid ,quantity FROM orderhistGO

USE northwindSELECT productid, SUM(quantity) AS total_quantity FROM orderhist GROUP BY productid HAVING SUM(quantity)>=30GO

productidproductid total_quantitytotal_quantity2 35

3 45

productidproductid orderidorderid quantityquantity1 1 5

1 1 10

2 1 10

2 2 25

3 1 15

3 2 30

Generating Aggregate Values Within Result Sets

Using the GROUP BY Clause with the ROLLUP Operator Using the GROUP BY Clause with the CUBE Operator Using the GROUPING Function

Description

Using the GROUP BY Clause with the ROLLUP OperatorUSE northwindSELECT productid, orderid, SUM(quantity) AS total_quantity FROM orderhist GROUP BY productid, orderid WITH ROLLUP ORDER BY productid, orderidGOproductidproductid orderidorderid total_quantitytotal_quantity

NULL NULL 951 NULL 151 1 51 2 102 NULL 352 1 102 2 253 NULL 453 1 153 2 30

Grand total

Summarizes only rows for productid 1Detail value for productid 1, orderid 1Detail value for productid 1, orderid 2Summarizes only rows for productid 2Detail value for productid 2, orderid 1Summarizes only rows for productid 3Detail value for productid 3, orderid 1Detail value for productid 3, orderid 2

Using the GROUP BY Clause with the CUBE Operator

The CUBE operatorproduces two more summaryvalues than theROLLUP operator

USE northwindSELECT productid, orderid, SUM(quantity) AS total_quantity FROM orderhist GROUP BY productid, orderid WITH CUBE ORDER BY productid, orderidGO

DescriptionGrand total

Summarizes all rows for orderid 1Summarizes all rows for orderid 2Summarizes only rows for productid 1Detail value for productid 1, orderid 1Detail value for productid 1, orderid 2Summarizes only rows for productid 2Detail value for productid 2, orderid 1Detail value for productid 2, orderid 2Summarizes only rows for productid 3Detail value for productid 3, orderid 1Detail value for productid 3, orderid 2

productidproductid orderidorderid total_quantitytotal_quantityNULL NULL 95NULL 1 30NULL 2 65

1 NULL 151 1 51 2 102 NULL 352 1 102 2 253 NULL 453 1 153 2 30

1 represents summary values in the preceding column

0 represents detail values in the preceding column

953065155

10351025451530

Using the GROUPING FunctionSELECT productid, GROUPING (productid) ,orderid, GROUPING (orderid) ,SUM(quantity) AS total_quantity FROM orderhist GROUP BY productid, orderid WITH CUBE ORDER BY productid, orderidGO

productidproductidNULLNULLNULL

111222333

111000000000

orderidorderidNULL

12

NULL12

NULL12

NULL12

100100100100

total_quantitytotal_quantity

Using the COMPUTE and COMPUTE BY ClausesCOMPUTE BYCOMPUTE

USE northwindSELECT productid, orderid, quantity FROM orderhist ORDER BY productid, orderid COMPUTE SUM(quantity) BY productid COMPUTE SUM(quantity)GO

USE northwindSELECT productid, orderid ,quantity FROM orderhistORDER BY productid, orderidCOMPUTE SUM(quantity)GO

productidproductid orderidorderid quantityquantity1 1 51 2 102 1 102 2 253 1 153 2 30

sum 95

productidproductid orderidorderid quantityquantity1 1 51 2 10

sum 152 1 102 2 25

sum 353 1 153 2 30

sum 45sum 95

Using Aliases for Table Names

Example 1 (without an alias name)

Example 2 (with an alias name)USE joindbSELECT buyer_name, s.buyer_id, qty FROM buyers AS b INNER JOIN sales AS s ON b.buyer_id = s.buyer_idGO

USE joindb SELECT buyer_name, sales.buyer_id, qty FROM buyers INNER JOIN sales ON buyers.buyer_id = sales.buyer_idGO