1 creating and maintaining database objects part 1 database systems

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Creating and MaintainingDatabase Objects

Part 1

Database Systems

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Script: text file that contains a sequence of SQL commands

Running a script:SQL> START path_to_script_file;

Path cannot contain any blank spaces

SQL Scripts

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Syntax:INSERT INTO tablename VALUES

(column1_value, column2_value, …);

You must insert a value or a NULL placeholder for every field

Fields must be entered in the order they appear in the table when you issue the DESC command

Inserting a Value Into EveryField in a Record

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Inserting a Value Into EveryField in a Record

• Example:

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Command to insert values for selected record fields:

INSERT INTO tablename

(column1_name, column2_name, …)

VALUES

(column1_value, column2_value, …);

Inserting Selected Table Fields

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Example:

Inserting Selected Table Fields

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Date values must be converted from characters to dates using the TO_DATE function and a format mask

Example:

Inserting Date Values

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Must be enclosed in single quotes Is case-sensitive To insert a string with a single

quote, type the single quote twice Example:'Mike''s Motorcycle Shop'

Inserting Text Data

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Transaction Logical unit of work consisting of one or

more SQL DML commands INSERT, UPDATE, DELETE

All transaction commands must succeed or none can succeed

Transaction results are not visible to other users until they are “committed” to the database

Until a transaction is committed, it can easily be “rolled back” (undone)

Transactions

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A transaction starts when you type one or more commands in SQL*Plus

A transaction ends when you issue either the COMMIT or ROLLBACK command

SQL>COMMIT;

SQL>ROLLBACK;

Transactions

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Committing and Rolling Back Data

• COMMIT• Makes transaction command changes

permanent in the database and visible to other users

• ROLLBACK• Rolls back transaction command

changes and restores database to its state before the transaction

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Used to mark individual sections of a transaction

You can roll back a transaction to a savepoint

Savepoints

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Syntax:UPDATE tablename

SET column1 = new_value,

column2 = new_value, …

WHERE search_condition;

Records can be updated in only one table at a time

Can update multiple records if they all match the search condition

Updating Records

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Format:WHERE fieldname operator expression

Operators Equal (=) Greater than, Less than (>, <) Greater than or Equal to (>=) Less than or Equal to (<=) Not equal (< >, !=, ^= LIKE BETWEEN IN NOT IN

Search Conditions

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WHERE s_name = ‘Sarah’

WHERE s_age > 18

WHERE s_class <> ‘SR’

Text in single quotes is case sensitive

Search Condition Examples

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Syntax:DELETE FROM tablenameWHERE search_condition;

Deletes multiple records if search condition specifies multiple records

If search condition is omitted, all table records are deleted

You can’t delete a record if it contains a primary key value that is referenced as a foreign key

Deleting Records

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Truncating Tables

• Removes all table data without saving any rollback information• Advantage: fast way to delete table

data• Disadvantage: can’t be undone

• Syntax:TRUNCATE TABLE tablename;

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Sequential list of numbers that is automatically generated by the database

Used to generate values for surrogate keys

Sequences

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Syntax:CREATE SEQUENCE sequence_name

[optional parameters];

Example:CREATE SEQUENCE f_id_sequence

START WITH 200;

Creating Sequences

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Viewing Sequence Information

• Query the SEQUENCE Data Dictionary View:

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Pseudocolumns

• Acts like a column in a database query

• Actually a command that returns a specific values

• Used to retrieve:• Current system date • Name of the current database user• Next value in a sequence

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Pseudocolumn Examples

PseudocolumnName

Output

CURRVAL Most recently retrieved sequence value

NEXTVAL Next value in a sequence

SYSDATE Current system date from database server

USER Username of current user

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Retrieving the current system date:SELECT SYSDATEFROM DUAL;

• Retrieving the name of the current user:

SELECT USERFROM DUAL;

DUAL is a system table that is used with pseudocolumns

Using Pseudocolumns

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Accessing the next value in a sequence:

sequence_name.NEXTVAL

Inserting a new record using a sequence:

INSERT INTO my_faculty VALUES

(f_id_sequence.nextval, ‘Professor Jones’);

Using PseudocolumnsWith Sequences

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• Permissions that you can grant to other users to allow them to access or modify your database objects

• Granting object privileges:GRANT privilege1, privilege2, …ON object_nameTO user1, user 2, …;

• Revoking object privileges:REVOKE privilege1, privilege2, …ON object_nameFROM user1, user 2, …;

Object Privileges

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Examples of Object Privileges

Object Type Privilege Description

Table, Sequence

ALTER Allows user to change object’s structure using the ALTER command

Table, Sequence

DROP Allows user to drop object

Table, Sequence

SELECT Allows user to view object

Table INSERT, UPDATE, DELETE

Allows user to insert, update, delete table data

Any database object

ALL Allows user to perform any operation on object

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Granting and Revoking Object Privileges

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Syntax:

SELECT column1, column2, …

FROM tablename

WHERE search_condition;

Retrieving Data From a Single Table

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To retrieve every column in a table:SELECT * FROM …

To retrieve every record in a table, omit the search conditionSELECT column1, column2, …

FROM tablename;

Retrieving Data From a Single Table

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Qualifying Table Names

• If you retrieve data from a table that is owned by another user, you must qualify the table name by prefacing it with the owner’s name

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Sometimes queries retrieve duplicate records

To suppress duplicate outputs, use the DISTINCT qualifier:SELECT DISTINCT column1, column2, …

FROM ...

Suppressing Duplicate Records

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Combining search conditions AND: both conditions must be true OR: either condition can be true

Combining AND and OR in a single operation AND comparisons are evaluated first Always use parentheses to force

conditions to be evaluated in the correct order

Using Multiple Search Conditions

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NULL: not defined Use IS NULL search condition

SELECT s_name, s_class

FROM my_students

WHERE s_class IS NULL;

Searching for NULL Records

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Use IS NOT NULL operator

SELECT s_name, s_age

FROM my_students

WHERE s_class IS NOT NULL;

Searching for NOT NULL Records

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Using the IN and NOT IN Operators

• IN retrieves all values where the search column value matches a set of values

SELECT *

FROM enrollment

WHERE grade IN (‘A’, ‘B’);

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Using the IN and NOT IN Operators

• NOT IN retrieves all values where the search column value matches a set of values

SELECT *

FROM enrollment

WHERE grade NOT IN (‘A’, ‘B’);

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Using the LIKE Operator

• Performs inexact searches by matching part of a character string

WHERE fieldname LIKE character_string;

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Using the LIKE Operator

• Character string must be in single quotes and use wildcard characters• % represents multiple wildcard characters• _ represents a single wildcard character• Wildcard characters can be placed at

beginning or end of string

• Examples:WHERE s_class LIKE ‘_R’;WHERE s_name LIKE ‘J%’;

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Use the ORDER BY clause Specify sort key, which is

column by which output is sorted

SELECT s_name, s_age

FROM my_students

ORDER BY s_age;

Sorting Query Output

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Default sort order Numerical: ascending Character: A - Z Date: oldest - newest To force the sort order: use ASC or

DESC Example

SELECT s_name, s_ageFROM my_studentsORDER BY s_age DESC;

Sorting Query Data

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Arithmetic operations on retrieved data Addition (+) Subtraction (-) Multiplication (*) Division (/)

Example:SELECT inv_id, qoh*price

FROM inventory;

Using Calculations in Queries

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ABS - absolute value CEIL – rounds a number up to the next integer FLOOR – rounds a number down to the

previous integer MOD – returns the remainder of a number and

a divisor POWER - raises a number to an exponent ROUND - rounds a number SQRT – returns the square root of a value TRUNC - truncates a number to the nearest

whole number

Single-RowNumber Functions

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Example:SELECT s_name,

TRUNC((SYSDATE - s_dob)/365)

FROM my_students;

Using Single-RowNumber Functions

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CONCAT – joins 2 character strings INITCAP – returns a string with the initial letter only

uppercase LENGTH – returns the length of a string LPAD, RPAD – returns a string with a specific number

of characters added on the left or right side LTRIM, RTRIM – returns a string with all instances of a

specific character trimmed from the left or right side REPLACE – replaces all instances of a character with

another character UPPER/LOWER – returns a string in all upper/lower

case letters

Single-RowCharacter Functions

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Example:SELECT UPPER(s_name)

FROM my_students;

Using Single-RowCharacter Functions

End of Lecture