IFS180.81 Intro. to Data Management

Chapter 8 Inner Joins

Joining Tables

Concept of linking together two or more tables, required if DB is 3rd normalized form

Create a result set of related information Create a result set based on matching values Returning columns in the result set Generally linking Primary Key and Foreign

Key. However, you can link any column.

Intersection Set Theory

Interested in finding commonality between two (or more sets)

Attributes describe the properties of each member

Set member is not simply the matching value (i.e. PK or FK values) but rather the entire row associated with the matching value

Intersections

Attributes:

Black Allister Seattle WA 166

Hallmark Joe Woodin WA 157

Ehrlich Zachary Seattle WA 143

Rojales Joe Tacoma WA 166

Patterson Rachel Auburn WA 157

Riser Brian Seattle WA 152

HindmanRick Duvall WA 145

Manken Don Bellevue WA 157

Rojales Joe Tacoma WA 166

Jones Fred Seattle WA 158

Intersections

Identification

Black Allister Seattle WA 166

Hallmark Joe Woodin WA 157

Ehrlich Zachary Seattle WA 143

Rojales Joe Tacoma WA 166

Patterson Rachel Auburn WA 157

Riser Brian Seattle WA 152

HindmanRick Duvall WA 145

Manken Don Bellevue WA 157

Rojales Joe Tacoma WA 166

Jones Fred Seattle WA 158

Last Name First Name City St Avg

5

10

7

15

17

1

3

8

15

20

Prim

ary Key

Tuesday League

Prim

ary Key

Monday League

Intersections

Intersection use to find equality between one or more data sets

Members inSeattle

Members Names Joe

Average > 160

Seattle and JoeSeattle, Joe, > 160

Intersection

Set theory intersection implemented in SQL standard with the (INNER) JOIN operation

Join on specific columns Creating a “Logical” table within the DB Join on any field as long as data types are

the same Performance issue Modify the from clause to contain two or more

table names from the DB Imperative to understand the relationships

between the tables

SQL JOIN

From Clause (single table)

From TABLENAME From Clause (multiple table)

From TABLENAME1 as T1 INNER JOIN

TABLENAME2 as T2

ON Search Condition - OR -

Using Column name Limited Support With multiple table reference, good practice dictates

the use of fully qualified names (table references) or (as per the SQL standard) Correlation Names

Join on column examples

Show me a list of bowling team names and the members on each team

Some DB’s do not support the Join statement, however tables can still be linked (PK or FK only) and use WHERE clause instead of the Join search criteria

Show me a listing of bowling team names, team members where raw scores between 150 and 155 Embedded Join

Join with Embedded Select Statements

Substitute a complete select statement for a table name

Requires a correlation name assigned to the embedded select (for reference purposes)

Embedded select may include all clauses except order by clause

In essence, query within a query and you must return any column and linking values for joins

Embedded Select Examples

Create a list of Team captain ID’s and names where the captain lives in Redmond

Create a list of Bowlers that have the same average.

Relationships

To be successful when joining tables it is imperative to understand the table relationships.

Most DB vendors provide a graphical format for viewing table relations.

Typically, these relationships are called ERD’s or Entity Relationship Diagrams