![21
Saving Table Changes
• Changes made to table contents are not
physically saved on disk until, one of the
following occurs:
– Database is closed
– Program is closed
– COMMIT command is used
• Syntax:
– COMMIT [WORK];
• Will permanently save any changes made
to any table in the database](https://image.slidesharecdn.com/introductiontostructuredquerylanguagesql1-230516065050-cc1c27cd/85/Introduction-to-Structured-Query-Language-SQL-1-ppt-21-320.jpg)
![23
Updating Table Rows
• UPDATE
– Modify data in a table
– Syntax:
• UPDATE tablename
SET columnname = expression [, columname =
expression]
[WHERE conditionlist];
• If more than one attribute is to be updated
in row, separate corrections with commas](https://image.slidesharecdn.com/introductiontostructuredquerylanguagesql1-230516065050-cc1c27cd/85/Introduction-to-Structured-Query-Language-SQL-1-ppt-23-320.jpg)
![25
Deleting Table Rows
• DELETE
– Deletes a table row
– Syntax:
• DELETE FROM tablename
[WHERE conditionlist ];
• WHERE condition is optional
• If WHERE condition is not specified, all
rows from specified table will be deleted](https://image.slidesharecdn.com/introductiontostructuredquerylanguagesql1-230516065050-cc1c27cd/85/Introduction-to-Structured-Query-Language-SQL-1-ppt-25-320.jpg)
![27
Selecting Rows with
Conditional Restrictions
• Select partial table contents by placing
restrictions on rows to be included in
output
– Add conditional restrictions to SELECT
statement, using WHERE clause
• Syntax:
– SELECT columnlist
FROM tablelist
[ WHERE conditionlist ] ;](https://image.slidesharecdn.com/introductiontostructuredquerylanguagesql1-230516065050-cc1c27cd/85/Introduction-to-Structured-Query-Language-SQL-1-ppt-27-320.jpg)
Introduction to Structured Query Language (SQL) (1).ppt
- 1. Introduction to Structured Query Language (SQL)
- 2. 2 Objectives • Explore basic commands and functions of SQL • How to use SQL for data administration (to create tables, indexes, and views) • How to use SQL for data manipulation (to add, modify, delete, and retrieve data) • How to use SQL to query a database to extract useful information
- 3. 3 Introduction to SQL • SQL functions fit into two broad categories: – Data definition language • SQL includes commands to: – Create database objects, such as tables, indexes, and views – Define access rights to those database objects – Data manipulation language • Includes commands to insert, update, delete, and retrieve data within database tables
- 4. 4 Introduction to SQL (continued) • SQL is relatively easy to learn • Basic command set has vocabulary of less than 100 words • Nonprocedural language • American National Standards Institute (ANSI) prescribes a standard SQL • Several SQL dialects exist
- 5. 5 Introduction to SQL (continued)
- 6. 6 Introduction to SQL (continued)
- 7. 7 Introduction to SQL (continued)
- 8. 8 Data Definition Commands • Examine simple database model and database tables that will form basis for many SQL examples • Understand data environment
- 10. 10 Creating the Database • Following two tasks must be completed: – Create database structure – Create tables that will hold end-user data • First task: – RDBMS creates physical files that will hold database – Tends to differ substantially from one RDBMS to another
- 11. 11 The Database Schema • Authentication – Process through which DBMS verifies that only registered users are able to access database – Log on to RDBMS using user ID and password created by database administrator • Schema – Group of database objects—such as tables and indexes—that are related to each other
- 12. 12 Data Types • Data type selection is usually dictated by nature of data and by intended use • Pay close attention to expected use of attributes for sorting and data retrieval purposes
- 14. 14 Creating Table Structures • Use one line per column (attribute) definition • Use spaces to line up attribute characteristics and constraints • Table and attribute names are capitalized • NOT NULL specification • UNIQUE specification
- 15. 15 Creating Table Structures (continued) • Primary key attributes contain both a NOT NULL and a UNIQUE specification • RDBMS will automatically enforce referential integrity for foreign keys • Command sequence ends with semicolon
- 16. 16 SQL Constraints • NOT NULL constraint – Ensures that column does not accept nulls • UNIQUE constraint – Ensures that all values in column are unique • DEFAULT constraint – Assigns value to attribute when a new row is added to table • CHECK constraint – Validates data when attribute value is entered
- 17. 17 SQL Indexes • When primary key is declared, DBMS automatically creates unique index • Often need additional indexes • Using CREATE INDEX command, SQL indexes can be created on basis of any selected attribute • Composite index – Index based on two or more attributes – Often used to prevent data duplication
- 18. 18 Data Manipulation Commands • Adding table rows • Saving table changes • Listing table rows • Updating table rows • Restoring table contents • Deleting table rows • Inserting table rows with a select subquery
- 19. 19 Adding Table Rows • INSERT – Used to enter data into table – Syntax: • INSERT INTO columnname VALUES (value1, value2, … , valuen);
- 20. 20 Adding Table Rows (continued) • When entering values, notice that: – Row contents are entered between parentheses – Character and date values are entered between apostrophes – Numerical entries are not enclosed in apostrophes – Attribute entries are separated by commas – A value is required for each column • Use NULL for unknown values
- 21. 21 Saving Table Changes • Changes made to table contents are not physically saved on disk until, one of the following occurs: – Database is closed – Program is closed – COMMIT command is used • Syntax: – COMMIT [WORK]; • Will permanently save any changes made to any table in the database
- 22. 22 Listing Table Rows • SELECT – Used to list contents of table – Syntax: • SELECT columnlist FROM tablename; • Columnlist represents one or more attributes, separated by commas • Asterisk can be used as wildcard character to list all attributes
- 23. 23 Updating Table Rows • UPDATE – Modify data in a table – Syntax: • UPDATE tablename SET columnname = expression [, columname = expression] [WHERE conditionlist]; • If more than one attribute is to be updated in row, separate corrections with commas
- 24. 24 Restoring Table Contents • ROLLBACK – Used to restore database to its previous condition – Only applicable if COMMIT command has not been used to permanently store changes in database • Syntax: – ROLLBACK; • COMMIT and ROLLBACK only work with data manipulation commands that are used to add, modify, or delete table rows
- 25. 25 Deleting Table Rows • DELETE – Deletes a table row – Syntax: • DELETE FROM tablename [WHERE conditionlist ]; • WHERE condition is optional • If WHERE condition is not specified, all rows from specified table will be deleted
- 26. 26 Inserting Table Rows with a Select Subquery • INSERT – Inserts multiple rows from another table (source) – Uses SELECT subquery • Query that is embedded (or nested) inside another query • Executed first – Syntax: • INSERT INTO tablename SELECT columnlist FROM tablename;
- 27. 27 Selecting Rows with Conditional Restrictions • Select partial table contents by placing restrictions on rows to be included in output – Add conditional restrictions to SELECT statement, using WHERE clause • Syntax: – SELECT columnlist FROM tablelist [ WHERE conditionlist ] ;
- 28. 28 Selecting Rows with Conditional Restrictions (continued)
- 29. 29 Selecting Rows with Conditional Restrictions (continued)
- 30. 30 Arithmetic Operators: The Rule of Precedence • Perform operations within parentheses • Perform power operations • Perform multiplications and divisions • Perform additions and subtractions
- 31. 31 Arithmetic Operators: The Rule of Precedence (continued)
- 32. 32 Special Operators • BETWEEN – Used to check whether attribute value is within a range • IS NULL – Used to check whether attribute value is null • LIKE – Used to check whether attribute value matches given string pattern
- 33. 33 Special Operators (continued) • IN – Used to check whether attribute value matches any value within a value list • EXISTS – Used to check if subquery returns any rows
- 34. 34 Advanced Data Definition Commands • All changes in table structure are made by using ALTER command – Followed by keyword that produces specific change – Following three options are available: • ADD • MODIFY • DROP
- 35. 35 Changing a Column’s Data Type • ALTER can be used to change data type • Some RDBMSs (such as Oracle) do not permit changes to data types unless column to be changed is empty
- 36. 36 Changing a Column’s Data Characteristics • Use ALTER to change data characteristics • If column to be changed already contains data, changes in column’s characteristics are permitted if those changes do not alter the data type
- 37. 37 Adding a Column • Use ALTER to add column – Do not include the NOT NULL clause for new column
- 38. 38 Dropping a Column • Use ALTER to drop column – Some RDBMSs impose restrictions on the deletion of an attribute
- 40. 40 Copying Parts of Tables • SQL permits copying contents of selected table columns so that the data need not be reentered manually into newly created table(s) • First create the PART table structure • Next add rows to new PART table using PRODUCT table rows
- 41. 41 Adding Primary and Foreign Key Designations • When table is copied, integrity rules do not copy, so primary and foreign keys need to be manually defined on new table • User ALTER TABLE command – Syntax: • ALTER TABLE tablename ADD PRIMARY KEY(fieldname); • For foreign key, use FOREIGN KEY in place of PRIMARY KEY
- 42. 42 Deleting a Table from the Database • DROP – Deletes table from database – Syntax: • DROP TABLE tablename;
- 43. 43 Advanced Select Queries • SQL provides useful functions that can: – Count – Find minimum and maximum values – Calculate averages • SQL allows user to limit queries to only those entries having no duplicates or entries whose duplicates may be grouped
- 49. 49 Grouping Data
- 52. 52 Virtual Tables: Creating a View • View is virtual table based on SELECT query – Can contain columns, computed columns, aliases, and aggregate functions from one or more tables • Base tables are tables on which view is based • Create view by using CREATE VIEW command
- 53. 53 Virtual Tables: Creating a View (continued)
- 54. 54 Joining Database Tables • Ability to combine (join) tables on common attributes is most important distinction between relational database and other databases • Join is performed when data are retrieved from more than one table at a time • Join is generally composed of an equality comparison between foreign key and primary key of related tables
- 55. 55 Joining Tables with an Alias • Alias can be used to identify source table • Any legal table name can be used as alias • Add alias after table name in FROM clause – FROM tablename alias
- 56. 56 Summary • SQL commands can be divided into two overall categories: – Data definition language commands – Data manipulation language commands • The ANSI standard data types are supported by all RDBMS vendors in different ways • Basic data definition commands allow you to create tables, indexes, and views
- 57. 57 Summary (continued) • DML commands allow you to add, modify, and delete rows from tables • The basic DML commands are SELECT, INSERT, UPDATE, DELETE, COMMIT, and ROLLBACK • INSERT command is used to add new rows to tables • SELECT statement is main data retrieval command in SQL
- 58. 58 Summary (continued) • Many SQL constraints can be used with columns • The column list represents one or more column names separated by commas • WHERE clause can be used with SELECT, UPDATE, and DELETE statements to restrict rows affected by the DDL command
- 59. 59 Summary (continued) • Aggregate functions – Special functions that perform arithmetic computations over a set of rows • ORDER BY clause – Used to sort output of SELECT statement – Can sort by one or more columns and use either an ascending or descending order • Join output of multiple tables with SELECT statement
- 60. 60 Summary (continued) • Natural join uses join condition to match only rows with equal values in specified columns • Right outer join and left outer join used to select rows that have no matching values in other related table