1. Introduction to Databases Chapter 6: Understanding the SQL Language

2. Introducing the SQL Language Two primary aspects: –Data definition: Requires data definition language (DDL) that defines tables, attributes, and indexes in DBMS –Data manipulation: Requires data manipulation language (DML) for issuing data manipulation commands to DBMS

3. Introducing the SQL Language Data retrieval statements: –Sometimes placed in different category, (separate from DML), as data query language (DQL) statements SQL: –Standard current relational DBMS language –Incorporates DDL and DML features

4. SQL Features ANSI SQL standard Basic features of standard SQL: –Data definition language (DDL): Used to create and maintain database objects –Data manipulation language (DML): Used to retrieve and manipulate data –Command operators: Symbols and keywords used to run arithmetic, comparison, and logical operations –Functions: Special executables that return values –Transaction control: Statements to initiate and complete or abort transaction processing

5. Using SQL Two basic options for executing SQL commands: –Interactive SQL: SQL statements that you run directly, interacting with database server –Embedded SQL: SQL functionality embedded in procedure or part of application written in different programming language

6. Interactive SQL All DBMS provide command interface or command prompt for running interactive SQL commands Microsoft SQL Server - Two options: –Command prompt: Issuing statements one at a time or several in set or batch –Loading and running scripts, groups of SQL Server commands stored as file Text-based interfaces: Complex, but allow execution of SQL language commands through batch files Some DBMS also have graphic user interface (GUI)

7. Sqlcmd Command Interface

8. SQL Server Management Studio

9. Embedded SQL Uses same SQL language commands as interactive SQL statements Are included as part of executable program –For example: SQL Server’s stored procedures and user-defined functions, which provide embedded SQL support Also used in application programs: –Programming environment provides connectivity tools to communicate with database server and execute SQL commands

10. Command Basics Command syntax: –Includes command name and any command keywords and parameters Command keywords: –Describe specific actions that command will take Command parameters: –Values supplied so command can run Example: SELECT select_list FROM table [WHERE qualifying_conditions]

11. Command Basics Commands typically run in context of default database –Each connection will have associated user Query results vary according to command: –SELECT command returns result set (relational result) of columns and rows –DML statements usually return count of rows affected

12. The SELECT Command SELECT commands: Declarative statements (not procedural) Relational DBMS: –Analyzes SQL SELECT statement –Creates access path—plan for steps to take in responding to query SQL SELECT commands can be run in interactive query or embedded mode

13. Example: Simple Data Retrieval

14. To find commission percentage and year of hire of salesperson 186: SELECT COMMPERCT, YEARHIRE FROM SALESPERSON WHERE SPNUM=186 To retrieve entire record for salesperson 186: SELECT * FROM SALESPERSON WHERE SPNUM=186 To list salesperson number and salesperson name of all of salespersons: SELECT SPNUM, SPNAME FROM SALESPERSON To return all rows and columns of data in Salesperson table: SELECT * FROM SALESPERSON

15. Retrieving Other Values In Microsoft SQL Server, SELECT statement can be used to evaluate expressions –Syntax: SELECT expression Expression: Any mathematical or logical expression that returns result For example: SELECT 5 + 7 will return “12” Syntax for resolving function: SELECT function [(parameter_list)]

16. Operators and Functions SQL operators: –Arithmetic operators –Logical operators Used in WHERE clause to build search conditions that depend on more than one qualifying condition Unary operator: –Operator applied to only one operand –Typical format : operator operand –For example: NOT A Binary operator: –Operator applied to two operands –Typical format: operand operator operand –For example: A OR B

17. Arithmetic Operators

18. To add two values: SELECT 5+ 5 total_value To concatenate two values as strings: SELECT ‘5’ + ‘5’ total_value Data type may affect precision and scale of result of arithmetic operation

19. Comparison Operators

20. Can be used: –In SELECT statement’s WHERE clause –With decision statements; for example: If A>B, then perform action –By themselves or together with logical operators

21. Logical Operators

22. Used to evaluate set of conditions Return results of TRUE, FALSE, or “unknown” Can be used: –In SELECT statement WHERE clause –With decision statements; for example: If A AND B are true, then perform action

23. Example: Comparison and Logical Operators

24. To list customer numbers, customer names, and headquarter cities of customers that are headquartered in New York or that satisfy two conditions: having customer number higher than 1500 and being headquartered in Atlanta SELECT CUSTNUM, CUSTNAME, HQCITY FROM CUSTOMER WHERE HQCITY=’New York’ OR (CUSTNUM>1500 AND HQCITY=’Atlanta’) Note that: –AND has higher precedence than OR –Clauses in parentheses evaluated first

25. The Like Operator

26. Used when criteria in WHERE clause of SELECT query are only partially known –For example, to find records for customers whose names begin with letter A SELECT * FROM CUSTOMER WHERE CUSTNAME LIKE ‘A%’

27. Standard SQL Functions Functions supported by various DBMS providers vary widely from ANSI standard function list and from each other Deterministic functions: –Always return same result if you pass in same arguments –E.g. ABS: Returns absolute value of number Nondeterministic functions: –May return different results when called with same arguments –E.g. GETDATE( ): Accepts no arguments and returns only current date and time

28. General Function Categories Numeric –Functions that operate with numbers –Statistical functions (e.g. mean and standard deviations) –Random number generator Mathematical –Perform specific mathematic calculations –For example, trigonometric functions for SIN, COS, and so forth

29. General Function Categories Date/Time –Performing calculations on dates and times, for example: Current date/time information Formatting date and time strings Performing calculations based on date and time Aggregate –Used to generate aggregate values based on sets of numeric values –For example, generating total, count, or average

30. General Function Categories String –Perform string manipulations such as: Modifying strings Locating patterns within string Inserting characters Concatenating strings Finding string length Changing character case Conversion –Used to convert values between data types –Allow explicit conversions between otherwise incompatible types

31. Sample SQL Functions Standard SQL-99 functions include: –BIT_LENGTH –CAST –CURRENT_DATE –SUBSTRING –UPPER SQL Server built-in aggregate functions include: –AVG –COUNT –MAX –SUM

32. DML Commands Three basic DML statements (ANSI SQL): –INSERT: To add rows to table –UPDATE: To modify values in existing columns and rows –DELETE: To remove rows from tables Statements may be subject to constraints or other limits placed on table –E.g. Foreign key constraint may disallow deletion of row referenced in another table

33. DDL Commands DDL commands are used to create and manage server and database objects –Server objects: Objects implemented at server level –Database objects: Database-specific objects, such as tables DDL commands vary widely in how they are implemented by various DBMSs

34. DDL Commands Three basic object management commands: –CREATE To create server and database objects, such as: – CREATE TABLE and CREATE INDEX –ALTER: To modify server and database objects, such as: – ALTER TABLE and ALTER INDEX –DROP: To delete server and database objects, such as: –DROP TABLE and DROP INDEX

35. Summary SQL: Standard relational DBMS language developed by ANSI that incorporates data definition language (DDL) and DML (data manipulation language (DML) features SQL commands follow specified syntax structure, using command name, command keywords, and parameters SQL commands feature arithmetical, comparison, and logical operators to modify queries and results Different SQL vendors may provide different functions, in categories such as mathematical, numeric, date/time, aggregate, string, conversion DML commands include INSERT, UPDATE, and DELETE DDL commands include CREATE, ALTER, and DROP

36. Key Terms Access path Aggregate function Batch Binary Operator Built-in functions Clause Command operators Command syntax Data definition language (DDL) Data manipulation language (DML) Data query language (DQL) Declarative statement Default database Deterministic function Domain Dynamic SQL Embedded SQL Explicit conversion Function Implicit conversion Interactive SQL

37. Key Terms Keyword Minimally logged operation Non-logged operation Nondeterministic function Operator precedence Parameters Parsing Procedure Qualifying conditions Query mode Relational result Result set Script Search argument Sqlcmd Subquery Temporary table Transaction control User-defined data type Unary operator Working database

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