Using SQL Queries to Insert, Update, Delete, and View Data

A Guide to Oracle9i 1

Using SQL Queries to Insert,Update, Delete, and View Data

Chapter 3


Lesson A Objectives

• Learn how to run a script to create database tables automatically

• Learn how to insert data into database tables• Learn how to create database transactions and commit

data to the database• Create search conditions in SQL queries• Understand how to update and delete database records,

and how to truncate tables• Learn how to create and use sequences to generate

surrogate key values automatically• Learn how to grant and revoke database object privileges


Using Scripts to Create Database Tables

• One or more SQL commands saved in a text file

• Usually have .sql extension• To run from SQL*Plus:

– Start full file path (c:\temp\myfile.sql)– @full file path (@c:\temp\myfile.sql)– Extension can be omitted if it is .sql


Inserting Data into Tables

• INSERT command adds new records• Field values should match column order, or be

specified in command• INSERT INTO faculty (F_ID, F_LAST, F_FIRST,

F_MI, LOC_ID) VALUES (1, 'Cox', 'Kim', 'J', 9);


Format Models

• Used to format data retrieved from database• Can be used to format a date to display time

or a number to display as a currency


Numerical Format Models


Date Format Models


Date Format Models


Inserting Date and Interval Values

• Use to_date function to convert a character string to a date– Specify date string and matching format model

– TO_DATE('08/24/2004', 'MM/DD/YYYY')

– TO_DATE('10:00 AM', 'HH:MI AM')

• Use functions to convert character strings to intervals– TO_YMINTERVAL('4-9') inserts a positive interval of 4 years, 9

months

– TO_DSINTERVAL('0 01:15:00') inserts a positive interval of 4 days, 1 hour, 15 minutes, 0 seconds


Inserting LOBs

• Before inserting LOB must insert a LOB locator

• LOB locator: a structure that contains information that identifies the LOB data type and points to the alternate memory location

• Write a program or use a utility to add LOB data to database

• Use EMPTY_BLOB() function to insert a LOB locator


Creating Transactions and Committing New Data

• Transaction: series of action queries that represent a logical unit of work

• User can commit (save) changes

• User can roll back (discard) changes

• Pending transaction: a transaction waiting to be committed or rolled back

• Oracle DBMS locks records associated with pending transactions

• Other users cannot view or modify locked records


Commit and Roll Back in SQL*Plus• Transactions begin automatically with first command• Type COMMIT to commit changes• Type ROLLBACK to roll back changes


Savepoints• A bookmark that designates the beginning of an individual

section of a transaction• Changes are rolled back to savepoint


Creating Search Conditions in SQL Queries

• An expression that seeks to match specific table records

• Used in SELECT, UPDATE and DELETE statements• WHERE fieldname comparison_operator

search_expression• WHERE S_ID = 1


Comparison Operators


Defining Search Expressions

• Character strings – Must be enclosed in single quotes– Case sensitive

• Dates– Use to_date function with date string and format model

• Intervals– Use to_yminterval and to_dsinterval with interval string

format model


Creating Complex Search Conditions

• Combines multiple search conditions using the AND,OR, and NOT logical operators.

• AND – both conditions must be true• OR – one or both condition must be true• NOT – opposite of actual value• Use () to group logical operators


Updating and Deleting Existing Table Records

• UPDATE:– Updates field values in one or more records in a table

– Only one table may be updated at a time

– UPDATE tablename SET field1= new_value1, field2 = new_value2, ... WHERE search condition;

• DELETE:– Removes specific records from a database table

– If search condition is omitted, entire table data is removed

– DELETE FROM tablename WHERE search condition;


Updating and Deleting Existing Table Records

• TRUNCATE

– Removes all of the table data without saving any rollback information

– Must disable foreign key constraints before truncating table

– TRUNCATE TABLE tablename;


Sequences

• Sequential lists of numbers to create unique surrogate key values

• To use a sequence:– SELECT sequence_name.NEXTVAL FROM DUAL;– INSERT INTO location LOC_ID)

VALUES(loc_id_sequence.NEXTVAL);


Database Object Privileges

• Privileges must be granted so that other users can access objects in user schema

• GRANT privilege1, privilege2,…ON object_name TO user1,user2,...;

• REVOKE privilege1, privilege2,... ON object_name FROM user1, user2, ...;

• To grant or revoke privileges for everyone use PUBLIC as user


Lesson B Objectives

• Learn how to write SQL queries to retrieve data from a single database table

• Create SQL queries that perform calculations on retrieved data

• Use SQL group functions to summarize retrieved data


Retrieving Data from a Single Database Table

• SELECT fieldname1, fieldname2, ... FROM ownername.tablename WHERE search_condition;

• To select:– All rows omit where clause

– All fields, use *: SELECT * FROM …

– Only unique field values: SELECT DISTINCT fieldname

• Search condition:– Use comparison and logical operators

– IS NULL/IS NOT NULL to match/exclude NULL values

– IN/NOT IN to match set values

– LIKE with wildcards % and _ to match character strings


Sorting Query Output• Use ORDER BY sort_key_field(s)• Default order is ascending, use DESC to sort descending


Using Calculations in SQL Queries

• Calculations are performed by DBMS, result only sent to client• Can use arithmetic operators (+, -, *, /)• Place calculation in select clause: SELECT price * quantity

FROM …• Calculations can be performed on NUMBER, DATE and

INTERVAL fields only• Single-row functions: built in Oracle functions to perform

calculations and manipulate retrieved data values


Oracle9i SQL Group Functions• Group functions: perform an operation on a group of queried

rows and returns a single result


Group By

• Use to group output by the field with duplicate values and apply group functions to the grouped data


Having

• Use to place a search condition on results of group function calculations

• Like “WHERE” for group functions• HAVING group_function comparison_operator value• HAVING SUM(capacity) >= 100


Formatting Output in SQL*Plus

• To change default column headings:– Specify alternate column headings: SELECT fieldname1

"heading1_text", fieldname2 "heading2_text", ...

– Use an alias for column headings: SELECT fieldname1 AS alias_name1...

• To change SQL*Plus line and page size settings– Select Options/Environment on menu bar

– Modify linesize and pagesize to desired values


Formatting Numbers and Dates

• Use to_char function with format models• TO_CHAR(field_name, 'format_model')• SELECT inv_id, TO_CHAR(inv_price, '$99,999.99')

FROM inventory WHERE item_id = 1;


Lesson C Objectives

• Learn how to create SQL queries that join multiple tables

• Learn how to create nested SQL queries• Understand how to combine query results using set

operators• Create and use database views


Joining Multiple Tables

• Join: combine data from multiple database tables using foreign key references

• SELECT field1, field2, ... FROM table1, table2 WHERE table1.joinfield = table2.joinfield AND search_condition(s);

• If tables share field names, must prefix field in select with table name (table1.field1, table2.field1)

• Join condition: part of where clause indicating how tables are related (table1.foreign_key = table2.primary key)

• Search conditions can be added to join condition using AND operator


Inner Join• Join two tables based on values in one table being equal

to values in another table

• Also known as equality join, equijoin or natural join

• Returns results only if records exist in both tables


Joining Via Linking Table


Using a Query Design Diagram

• Helpful for creating complicated queries• Can use a formula to derive actual query from diagram


Outer Join

• Returns all rows in one table and matching rows in joined table

• Inner table: all rows are returned

• Outer table: matching rows are returned

• Outer table marked with a + in join condition

• inner_table.join_field = outer_table.join_field(+)

• Null values are inserted for fields in outer table that are not found


Self-Join

• A query that joins a table to itself

• Used when a table has a foreign key relationship to itself (usually parent-child relationship)

• Must create a table alias and structure the query as if you are joining the table to a copy of itself

• FROM table1 alias1, ...

• Use alias, not table name for select and where clauses


Self-Join Example


Creating Nested Queries

• Used to select results based on the result of a query• Consists of a main query and one or more subqueries.

– Main query: first query that appears in the SELECT command– Subquery retrieves values that the main query’s search condition

must match


Creating Nested Queries

• Nested queries can return single or multiple values– To match single values use = operator

– To match multiple values use IN operator

• Subqueries can be nested to more than one level (nested subqueries)

• Nested subqueries are slower than joins and should be used sparingly


Nested Subquery Example


Using Set Operators To Combine Query Results

• Use to select data from multiple tables not connected with foreign key relationships


Set Operators

• query1 OPERATOR query2; (where operator is UNION, UNION ALL, INTERSECT, or MINUS)

• Both queries must have same number of select fields and same data types in same order

• UNION suppresses duplicate values

• UNION ALL includes duplicate values

• INTERSECT takes only matching fields

• MINUS takes only fields in query1 not query2


Creating and Using Database Views

• Similar to storing the result of a query in the database

• Based on a source query that:– can specify a subset of a single table’s fields or records

– can join multiple tables

• Can be used to enforce security (user has access to view but not underlying table)


Creating and Using Database Views

• Views can be updateable if:– SELECT clause contains only fieldnames, no functions or

calculations

– cannot contain the ORDER BY, DISTINCT, or GROUP BY clauses, group functions, or set operators

– search condition cannot contain a nested query

• Views are used like tables for selecting, inserting, updating and deleting data (only updatable views can be modified)


Creating and Deleting Views

• CREATE OR REPLACE VIEW view_name AS source_query;• DROP VIEW viewname;


Summary

• Use INSERT commands to add data• NUMBER, DATE and INTERVAL data types can be converted

to and from character strings using format models• Database changes are made within a transaction that can be

committed or rolled back• Use search conditions to specify records to update, delete or

select• Arithmetic, logical, grouping, and built-in Oracle functions can

be used to specify search conditions and manipulate data• Query output can be formatted by modifying SELECT clause


Summary

• Results from more than one table related through foreign key relationships can be combined in a join

• Results from more than one unrelated table can be combined using set operators

• Queries can be “saved” by creating a view• Views can be used like tables to select, insert, update and

delete data

Documents

Using SQL Queries to Insert, Update, Delete, and View Data