1. ITBIS373 Database Development
Lecture3c - Chapter 3: Using SQL Queries to Insert, Update, Delete, and View Data
Guide to Oracle 10g

2. Lesson C Objectives
After completing this lesson, you should be able to:
Create SQL queries that join multiple tables
Create nested SQL queries
Combine query results using set operators
Create and use database views
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3. Joining Multiple Tables
Combine data from multiple database tables using foreign key references
Syntax
SELECT column1, column2, …
FROM table1, table2
WHERE table1.joincolumn = table2.joincolumn
AND search_condition(s);
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4. Joining Multiple Tables (continued)
Must qualify column name in SELECT clause
Specify name of table that contains column followed by period then column name
Join condition
Specifies table names to be joined and column names on which to join tables
SQL supports multiple types of join queries
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5. Inner Joins Simplest type of join
VALUES in one table equal to values in other table
Also called:
Equality join
Equijoin
Natural join
Query design diagram
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7. Fig 3-43 to retrieve the student Id, student last and first names, advisor ID, and advisor last name.
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8. In SQL queries, you can join any number of tables in SELECT command
In SQL queries, you can join any number of tables in SELECT command. When join tables, the name of each table in the query must appear in the FROM clause. This includes tables whose columns are display columns, which are columns that appear in the SELECT clause, and whose columns are search columns, which appear in search condition. The primary key and foreign key columns on which you join the tables are called join columns.
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9. When you join multiple tables, sometimes you must join the tables using an intermediary table whose columns are not display or search columns, but whose columns are join columns that serve to join the two tables.
For example, suppose you want to create a query that lists the last names of all faculty members who teach during the Summer 2007 term.
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10. Visual Representation of the Northwoods University Database
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14. A linking table does not contribute any as display columns or search condition columns, but contains join columns that link the other tables through shared foreign key values.
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15. STUDENT (to search for S_FIRST and S_LAST),
Some times queries that join multiple tables can become complex. For example, suppose that you want to create a query to display the COURSE_NO and GRADE values for each of student ‘Tammy Jones’ courses. This query requires you to join four table:
STUDENT (to search for S_FIRST and S_LAST),
ENROLLMENT (to display GRADE),
COURSE to display COURSE_NO), and
COURSE_SECTION (to join ENROLLMENT to COURSE using the C_SEC_ID join column).
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17. Deriving a SQL Query From a Query Design Diagram
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19. If you accidentally omit a join condition in a multiple-table query, the output retrieves more rows than you expect. When you omit a join condition, the query creates a Cartesian product, whereby every row in one table is joined with every row in the other table. For example , suppose you repeat the query to show each student row, along with each student’s advisor (see Fig 3-43), but you omit the join condition. Every row in the STUDENT table (six rows) is joined with every row in the FACULTY table (five rows). The result is 6 times 5 rows, or 30 rows.
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21. Outer Join
An inner join returns rows only if values exist in all tables that are joined. If no values exist for a row in one of the joined tables, the inner join does not retrieve the row. For example suppose you want to retrieve the different locations of the courses included in the COURSE_SECTION table.
This query requires joining rows in the LOCATION and COURSE_SECTION tables.
Not every location in the LOCATION table has an associated COURSE_SECTION row, so the query retrieves rows only for locations that have associated COURSE_SECTION rows.
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23. SQL> SELECT c_sec_id, location.loc_id
2 From course_section, location
3 Where course_section.loc.id = location.loc_id;
C_SEC_ID LOC_ID
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24. An outer join returns all rows from one table , which is called the inner table. An outer join also retrieves matching rows from a second table, which is called the outer table.
The query designer specifies which table is the inner table and which table is the outer table.
In this case, because you want to retrieve all of the rows in the LOCATION table, you specify LOCATION as the inner table.
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25. Outer Joins Returns all rows from one table
Called inner table
And matching rows from second table
Called outer table
Syntax
inner_table.join_column = outer_table.join_column(+)
The outer join operator (+) signals the DBMS to insert a NULL value for the columns in the outer table that do not have matching rows in the inner table.
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27. Self-Joins
Sometimes a relational database table contains a foreign key that references a column in the same table. For example, at Northwood's University each assistant and associate professor is assigned to full professor who serves as the junior professor’s supervisor.
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28. Self-Joins
To create a query that lists the names of each junior faculty member and the names of their supervisor, you must join the FACULTY table to itself.
When you create a query that joins a table to it self, you create a self-join.
To create a self-join, you must create a table alias and structure the query as if you are joining the table to a copy of itself.
The syntax to create a table alias in the FORM clause is:
FROM table1 alias1,……
When you create a table alias, you must the use the table alias, rather than the table name, to qualify column names in the SELECT clause and in join condition.
T o make the process easier to understand, you create two table aliases _FAC for faculty version of the table and SUPER for the supervisor version of the same table, as shown in Fig 3-51.
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31. Self Joins
PARENT_PROJECT
SUB_PROJECT
PROJECT
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32. Self Join Example
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33. Creating Nested Queries
Nested query
Consists of main query and one or more subqueries
Main query
First query that appears in SELECT command
Subquery
Retrieves values that main query’s search condition must match
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34. Creating Nested Queries with Subqueries that Return a Single Value
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35. The query in Fig 3-54 to retrieve the names of all students who have the same S_CLASS value as student Jorge Perez.
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36. Creating Subqueries that Return Multiple Values.
To create a nested query in which the subquery retrieves multiple values. You must use IN comparison operator instead of the equal to comparison operator.
Ex: To retrieve the names of all students who have enrolled in the same course sections as Jorge Perez. Note that the main query’s search conditions uses the IN comparison operator, because the sub-query returns multiple values.
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37. ENROLLEMENT S_ID C_SEC_ID GRADE PE100 1 B PE100 5 A PE100 6 B
JO C
JO C
JO C
MA B
JO C
JO C
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39. Using Multiple Subqueries Within a Nested Query
Use AND and OR operators
To join search conditions associated with subqueries.
Ex: Fig 3-53 is used to retrieve the names of all students who have the same S_CLASS value as Jorge Perez and who have also been enrolled in course section with him
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41. Creating Nested Subqueries
Nested subquery
Subquery that contains second subquery that specifies its search expression
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42. USING SET Operator to Combine Query Results
UNION set operator
Joins output of two unrelated queries into single output result
Syntax
query1 UNION query2;
Both queries must have the
same number of display columns in their SELECT clauses
must have the same data type
For example, if the display columns retuned by query1 are a NUMBER data column and then a VARCHAR2 data column, then the display columns returned by query2 must also be a NUMBER data column followed by a VARCHAR2 data column.
UNION ALL operator
Same as UNION but includes duplicate rows
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43. Ex: Create a telephone directory of every student and faculty member at Northwood's University
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44. INTERSECT Finds intersection in two queries
Requires that both queries have same number and data types of display columns in SELECT statement
Automatically suppresses duplicate rows.
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46. INTERSECT Some queries require an output that finds the intersection, or matching rows, in two unrelated queries. For example, suppose you need to find a list of faculty members whose offices are in the BUS building and who have also taught a course in the BUS building.
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47. MINUS To find difference between two unrelated query result list.
As with the UNION and INTERSECT operators, the MINUS operator requires that both queries have the same number of display columns in the SELECT statement, and that each column in the first query has the same data type as corresponding column in the second query.
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50. Creating and Using Database Views
Source query
Used to create view
Specify subset of single table’s columns or rows or join multiple tables
Updatable views
Can be used to update database
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51. Database Views Logical table based on a query
Does not physically exist in the database as table
Presents data in a different format from underlying tables
Uses:
Security
Simplifying complex queries
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52. Database Views Creating a view: CREATE VIEW view_name AS SQL_command;
Views can be queried just like tables:
SELECT *
FROM view_name;
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53. Simple Views
Based on SQL query that retrieves data from only one table
View can support all table DML operations:
INSERT
UPDATE
DELETE
Can also execute update action queries and delete action queries using view
Just as with database table
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54. Complex Views Based on query that retrieves data from multiple tables
Can only be used to support SELECT operations
No DML operations supported
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55. Creating Views
If there is possibility that you have already created a view using a specific name, you can use the following command to create or replace the existing view according to this syntax.
CREATE OR REPLACE VIEW view_name
AS source_query;
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56. Ex: This view contains all of the FACULTY columns except F_PIN and F_IMAGE
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57. Executing Action Queries Using Views
1- To insert a row using the FACULTY_VIEW
INSERT INTO faculty_view VALUE (6,’may’,’Lisa,’I’,11,’ ’,’INST’)
2- Type SELECT * FROM faculty_view; to determine whether the new faculty member is included in the table.
Type DELETE FROM faculty_view WHERE f-last =‘MAY’; to delete the new faculty member.
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58. Retrieving Rows from Views.
You can query a view using a SELECT statement, just as with a database table, and use the view in complex queries that involve join operations and subqueries.
You create a query that joins FACULTY_VIEW with the LOCATION to list the names of each faculty member, along with the building code and room number of the faculty member’s office.
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60. Removing Views DROP VIEW command Remove view from user schema Syntax
DROP VIEW view_name;
Ex: DROP VIEW faculty_view;
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61. Selecting Records For Update
Syntax:
SELECT column1, column2, …
FROM table1, table2, …
WHERE search and join conditions
FOR UPDATE OF column1, column2, …
NOWAIT;
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62. The NOWAIT command causes the system to generate an error message immediately if another user has previously locked the selected records. If the NOWAIT command is omitted, the system forces the user to “wait” until the requested records are unlocked, and the user can do no further processing.
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64. Dynamic SQL Queries
Queries that allow users to specify search conditions at runtime
Approaches
Substitution Values
Runtime Variables
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65. Using Substitution Values
Created when search expression is prefaced with an ampersand (&)
System then prompts user for value
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66. Using Runtime Variables
Runtime variable: variable defined in SQL*Plus environment
Syntax:
DEFINE variable_name = variable_value;
You can then substitute the variable name for a query search condition value
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67. Using Runtime Variables
Example:
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68. Indexes
Index: Separate table is maintained that shows index keys and physical locations of corresponding records
In Oracle, ROWID is translated to physical location of row on disk
Improves response time of searches and joins
SLName
ROWID
Brown
Jones
Smith
Helgeson
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69. Using Indexes Create table index AFTER table is populated with data
Indexes make INSERT, UPDATE, and DELETE operations slower because index must also be maintained
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70. Indexing Strategies A table can have indexes on multiple fields
Create indexes based on fields used for search or join operations
Typically, indexes only speed retrievals when <15% of the table records are involved
Each additional index adds processing overhead for INSERT, UPDATE, and DELETE operations
In Oracle, primary keys are automatically indexed
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71. Creating Indexes Syntax: CREATE INDEX index_name
ON tablename(index_field);
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72. Summary INSERT action query SQL search condition UPDATE action query
Match one or more database rows
UPDATE action query
DELETE command
SELECT query
DISTINCT qualifier
Single row and group functions
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73. Summary (continued) Can change appearance of SQL*Plus environment
Join multiple tables in SELECT query
Inner join
Outer join
Nested queries
Set operators
Views
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