SQL Workshop. Introduction Queries. Doug Shook

Transcription

1 SQL Workshop Introduction Queries Doug Shook

2 SQL Server As its name implies: its a data base server! Technically it is a database management system (DBMS) Competitors: Oracle, MySQL, DB2 End users (that s you!) interact as clients Queries formed on the client and passed to the server 2

3 SQL Server Database server ` Network ` Client Client ` Client 3

4 Relational database model Data is stored in tables One or more columns (fields) Many, many, rows (records) Modeled after real world entities Attributes Instances Primary keys are used to identify each record Must be unique! 4

5 Relational database model Primary key Columns Rows 5

6 Relational database model Relationships are defined between two tables by foreign keys One-to-one One-to-many Many-to-many Primary key -> foreign key 6

7 Relational database model Primary key Foreign key 7

8 Columns Columns have associated properties Data type Null? Default value Identity column 8

9 Comparison with file systems Databases... Are consistent Same basic structure for all data Are easier to maintain Due to centralization Can perform validations Can enforce relationships Can access many records at once Allow concurrent access Performance considerations? 9

10 SQL Forms the basis of all DBMS Basic statements will work (mostly) regardless of platform Each vendor adds extensions Two main categories Data Manipulation Language Data Definition Language 10

11 SQL SQL DML statements SELECT INSERT UPDATE DELETE SQL DDL statements CREATE DATABASE, TABLE, INDEX ALTER TABLE, INDEX DROP DATABASE, TABLE, INDEX 11

12 SQL Coding Guidelines Freeform Lines, spaces, linebreaks do not affect code Not case sensitive (!) Comments Block /* */ Single line -- 12

13 SQL Coding Guidelines Recommendations: Each clause should be on a new line Break up long clauses and indent Keywords should be capatalized (or in all caps) Column and table names should use CamelCase Each statement should end with a semicolon Technically not required by SQL Server but... 13

14 SQL Coding Guidelines A SELECT statement that s difficult to read select invoicenumber, invoicedate, invoicetotal, invoicetotal paymenttotal credittotal as balancedue from invoices where invoicetotal paymenttotal credittotal > 0 order by invoicedate A SELECT statement that s coded with a readable style Select InvoiceNumber, InvoiceDate, InvoiceTotal, InvoiceTotal PaymentTotal CreditTotal As BalanceDue From Invoices Where InvoiceTotal PaymentTotal CreditTotal > 0 Order By InvoiceDate; 14

15 Our Setup Server set up for us We'll be sharing...so be nice! Need a client DBVisualizer 15

16 Connecting to the DB Server name: supplied to you Authentication Username: washu Password: workshop 16

17 Database Diagrams Shows: Table relationships Column names Primary keys Great for visualizing the database as a whole 17

18 Queries Click the green triangle SQL Commander Ensure that the DB you d like to work with is selected in the combobox Type in the query Execute button Results displayed at the bottom Once a query works the way you want, save it! 18

19 Syntax Errors Sometimes detected by the query editor Common mistakes Wrong DB selected in combobox Misspellings Missing quotation/parentheses 19

20 Documentation Short version: Use it! Long version: It will save you time and effort. Use it! 20

21 SELECT Used to retrieve information (Up to) four clauses: SELECT Column name(s) FROM Table name WHERE (Optional) Conditional statement(s) ORDER BY (Optional) Column name(s) 21

22 SELECT Examples A simple SELECT statement SELECT * FROM Invoices; A SELECT statement that retrieves and sorts rows SELECT InvoiceNumber, InvoiceDate, InvoiceTotal FROM Invoices ORDER BY InvoiceTotal; A SELECT statement that retrieves a calculated value SELECT InvoiceID, InvoiceTotal, CreditTotal + PaymentTotal AS TotalCredits FROM Invoices WHERE InvoiceID = 17; A SELECT statement that retrieves all invoices between given dates SELECT InvoiceNumber, InvoiceDate, InvoiceTotal FROM Invoices WHERE InvoiceDate BETWEEN ' ' AND ' ' ORDER BY InvoiceDate; 22

23 Column Specifications The expanded syntax of the SELECT clause SELECT [ALL DISTINCT] [TOP n [PERCENT] [WITH TIES]] column_specification [[AS] result_column] [, column_specification [[AS] result_column]]... Five ways to code column specifications All columns in a base table Column name in a base table Arithmetic expression String expression Function 23

24 Column Specifications Column specifications that use base table values The * is used to retrieve all columns SELECT * Column names are used to retrieve specific columns SELECT VendorName, VendorCity, VendorState Column specifications that use calculated values An arithmetic expression is used to calculate BalanceDue SELECT InvoiceNumber, InvoiceTotal - PaymentTotal CreditTotal AS BalanceDue A string expression is used to calculate FullName SELECT VendorContactFName + ' ' + VendorContactLName AS FullName A function is used to calculate CurrentDate SELECT InvoiceNumber, InvoiceDate, GETDATE() AS CurrentDate 24

25 Naming Columns Two ways to name the columns in a result set Using the AS keyword (the preferred technique) SELECT InvoiceNumber AS [Invoice Number], InvoiceDate AS Date, InvoiceTotal AS Total FROM Invoices; Using the equal operator (an older technique) SELECT [Invoice Number] = InvoiceNumber, Date = InvoiceDate, Total = InvoiceTotal FROM Invoices; The result set for both SELECT statements 25

26 String Expressions How to concatenate string data SELECT VendorCity, VendorState, VendorCity + VendorState FROM Vendors; How to format string data using literal values SELECT VendorName, VendorCity + ', ' + VendorState + ' ' + VendorZipCode AS Address FROM Vendors; How to include apostrophes in literal values SELECT VendorName + '''s Address: ', VendorCity + ', ' + VendorState + ' ' + VendorZipCode FROM Vendors; 26

27 Functions A SELECT statement that uses the LEFT function SELECT VendorContactFName, VendorContactLName, LEFT(VendorContactFName, 1) + LEFT(VendorContactLName, 1) AS Initials FROM Vendors; A SELECT statement that uses the CONVERT function SELECT 'Invoice: #' + InvoiceNumber + ', dated ' + CONVERT(char(8), PaymentDate, 1) + ' for $' + CONVERT(varchar(9), PaymentTotal, 1) FROM Invoices; A SELECT statement that computes the age of an invoice SELECT InvoiceDate, GETDATE() AS 'Today''s Date', DATEDIFF(day, InvoiceDate, GETDATE()) AS Age FROM Invoices; 27

28 DISTINCT A SELECT statement that returns all rows SELECT VendorCity, VendorState FROM Vendors ORDER BY VendorCity; A SELECT statement that eliminates duplicate rows SELECT DISTINCT VendorCity, VendorState FROM Vendors; 28

29 TOP A SELECT statement with a TOP clause SELECT TOP 5 VendorID, InvoiceTotal FROM Invoices ORDER BY InvoiceTotal DESC; A SELECT statement with a TOP clause and the PERCENT keyword SELECT TOP 5 PERCENT VendorID, InvoiceTotal FROM Invoices ORDER BY InvoiceTotal DESC; A SELECT statement with a TOP clause and the WITH TIES keyword SELECT TOP 5 WITH TIES VendorID, InvoiceDate FROM Invoices ORDER BY InvoiceDate ASC; 29

30 WHERE Recall that this is optional! Examples of WHERE clauses that retrieve Vendors located in Iowa WHERE VendorState = 'IA' Invoices with a balance due (two variations) WHERE InvoiceTotal PaymentTotal CreditTotal > 0 WHERE InvoiceTotal > PaymentTotal + CreditTotal Vendors with names from A to L WHERE VendorName < 'M' Invoices on or before a specified date WHERE InvoiceDate <= ' ' Invoices on or after a specified date WHERE InvoiceDate >= '5/1/12' Invoices with credits that don t equal zero WHERE CreditTotal <> 0 30

31 Logical Operators The syntax of the WHERE clause with logical operators WHERE [NOT] search_condition_1 {AND OR} [NOT] search_condition_2... Examples of queries using logical operators The AND operator WHERE VendorState = 'NJ' AND YTDPurchases > 200 The OR operator WHERE VendorState = 'NJ' OR YTDPurchases > 200 The NOT operator WHERE NOT (InvoiceTotal >= 5000 OR NOT InvoiceDate <= ' ') The same condition without the NOT operator WHERE InvoiceTotal < 5000 AND InvoiceDate <= ' ' 31

32 IN The syntax of the WHERE clause with an IN phrase WHERE test_expression [NOT] IN ({subquery expression_1 [, expression_2]...}) Examples of the IN phrase An IN phrase with a list of numeric literals WHERE TermsID IN (1, 3, 4) An IN phrase preceded by NOT WHERE VendorState NOT IN ('CA', 'NV', 'OR') An IN phrase with a subquery WHERE VendorID IN (SELECT VendorID FROM Invoices WHERE InvoiceDate = ' ') 32

33 BETWEEN The syntax of the WHERE clause with a BETWEEN phrase WHERE test_expression [NOT] BETWEEN begin_expression AND end_expression Examples of the BETWEEN phrase A BETWEEN phrase with literal values WHERE InvoiceDate BETWEEN ' ' AND ' ' A BETWEEN phrase preceded by NOT WHERE VendorZipCode NOT BETWEEN AND A BETWEEN phrase with a test expression coded as a calculated value WHERE InvoiceTotal PaymentTotal CreditTotal BETWEEN 200 AND 500 A BETWEEN phrase with calculated values WHERE InvoiceDueDate BETWEEN GetDate() AND GetDate()

34 Dates Datetime data type includes date and time (duh) So what happens when you compare just the date to a datetime column? More about dates to come... 34

35 LIKE Used for matching string patterns Symbols %: match zero or more characters _: match any single character []: match anything contained within [ - ]: match anything within the given range [ ^ ]: match anything except what is given 35

36 LIKE WHERE clauses that use the LIKE phrase Example 1 WHERE VendorCity LIKE 'SAN%' Cities that will be retrieved San Diego and Santa Ana Example 2 WHERE VendorName LIKE 'COMPU_ER%' Vendors that will be retrieved Compuserve and Computerworld Example 3 WHERE VendorContactLName LIKE 'DAMI[EO]N' Names that will be retrieved Damien and Damion 36

37 LIKE WHERE clauses that use the LIKE phrase (cont.) Example 4 WHERE VendorState LIKE 'N[A-J]' States that will be retrieved NC and NJ but not NV or NY Example 5 WHERE VendorState LIKE 'N[^K-Y]' States that will be retrieved NC and NJ but not NV or NY Example 6 WHERE VendorZipCode NOT LIKE '[1-9]%' Zip codes that will be retrieved and

38 NULL What qualifies as NULL? 0? Empty string? ( ) A single space? ( ) 38

39 NULL A SELECT statement that retrieves rows with zero values SELECT * FROM NullSample WHERE InvoiceTotal = 0; A SELECT statement that retrieves rows with non-zero values SELECT * FROM NullSample WHERE InvoiceTotal <> 0; A SELECT statement that retrieves rows with null values SELECT * FROM NullSample WHERE InvoiceTotal IS NULL; A SELECT statement that retrieves rows without null values SELECT * FROM NullSample WHERE InvoiceTotal IS NOT NULL; 39

40 ORDER BY Can sort by one or more columns Sorts ascending by default Sorting order (ascending) Null Special Characters (&,!, etc.) Numbers Letters Can also use aliases, expressions, and column positions 40

41 ORDER BY An ORDER BY clause that sorts by one column in descending sequence SELECT VendorName, VendorCity + ', ' + VendorState + ' ' + VendorZipCode AS Address FROM Vendors ORDER BY VendorName DESC; An ORDER BY clause that sorts by three columns SELECT VendorName, VendorCity + ', ' + VendorState + ' ' + VendorZipCode AS Address FROM Vendors ORDER BY VendorState, VendorCity, VendorName; 41

42 ORDER BY An ORDER BY clause that uses an alias SELECT VendorName, VendorCity + ', ' + VendorState + ' ' + VendorZipCode AS Address FROM Vendors ORDER BY Address, VendorName; An ORDER BY clause that uses an expression SELECT VendorName, VendorCity + ', ' + VendorState + ' ' + VendorZipCode AS Address FROM Vendors ORDER BY VendorContactLName + VendorContactFName; An ORDER BY clause that uses column positions SELECT VendorName, VendorCity + ', ' + VendorState + ' ' + VendorZipCode AS Address FROM Vendors ORDER BY 2, 1; 42

43 ORDER BY OFFSET and FETCH can optionally be used to retrieve a range of rows OFFSET: Starting position FETCH: Number to retrieve after offset 43

44 ORDER BY The syntax of the ORDER BY clause for retrieving a range of rows ORDER BY order_by_list OFFSET offset_row_count {ROW ROWS} [FETCH {FIRST NEXT} fetch_row_count {ROW ROWS} ONLY] An ORDER BY clause that retrieves the first five rows SELECT VendorID, InvoiceTotal FROM Invoices ORDER BY InvoiceTotal DESC OFFSET 0 ROWS FETCH FIRST 5 ROWS ONLY; An ORDER BY clause that retrieves rows 11 through 20 SELECT VendorName, VendorCity, VendorState, VendorZipCode FROM Vendors WHERE VendorState = 'CA' ORDER BY VendorCity OFFSET 10 ROWS FETCH NEXT 10 ROWS ONLY; 44

45 45 Exercises Write a SELECT statement that returns three columns from the Vendors table: VendorContactFName, VendorContactLName, and VendorName. Sort the result set by last name, then by first name.

46 46 Exercises Write a SELECT statement that returns four columns from the Invoices table, named Number, Total, Credits, and Balance: Number Column alias for the InvoiceNumber column Total Column alias for the InvoiceTotal column Credits Sum of the PaymentTotal and CreditTotal columns Balance InvoiceTotal minus the sum of PaymentTotal and CreditTotal

47 47 Exercises Write a SELECT statement that returns one column from the Vendors table named Full Name. Create this column from the VendorContactFName and VendorContactLName columns. Format it as follows: last name, comma, first name (for example, "Doe, John"). Sort the result set by last name, then by first name.

48 48 Exercises Write a SELECT statement that returns three columns: InvoiceTotal From the Invoices table 10% 10% of the value of InvoiceTotal Plus 10% The value of InvoiceTotal plus 10% Only return those rows with a balance due greater than Sort the result set by InvoiceTotal, with the largest invoice first.

49 49 Exercises Modify the solution to the problem on slide 51 to filter for invoices with an InvoiceTotal that's greater than or equal to $500 but less than or equal to $10,000.

50 50 Exercises Modify the solution to the problem on slide 52 to filter for contacts whose last name begins with the letter A, B, C, or E.

51 51 Exercises Write a SELECT statement that determines whether the PaymentDate column of the Invoices table has any invalid values. To be valid, PaymentDate must be a null value if there's a balance due and a non-null value if there's no balance due. Code a compound condition in the WHERE clause that tests for these conditions.