Joins in report studio

8/10/2019 Joins in report studio

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Documentation Developed by Elisabetta Zodeiko, Princeton University

March 2011

Report Studio

Understanding Joins

Cardinality

Report Studio Joins, Intersects, Excepts, Unions


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Princeton University

Report Studio Joins pg. 2

From Cognos: in general, join relationships should be created in the Framework Manager model.

Create a join relationship in Report Studio if what you are trying to do cannot be modeled in

Framework Manager.

What is a Query?

SQL (Structured Query Language) is a standard language for accessing databases. An example of a

SQL statement used in an Oracle database is:

Select * from Personal_Data_Table where Last_Name = Smith;

Select * from Personal_Data_Table where Last Name = Smith;

Select all records from the Personal Data Table which have Smith as the

Last Name field. Thesemicolon ends the

statement.

What is a Join?

A Join is a relationship between two database tables, created to combine records from each table.

A Join is a combination of two database tables.

A Join Relationship Example:

The Person Table (containing personal columns) is joined to the Citizenship table (containing

citizenship columns) so that all the records, pertaining to both personal and citizenship, can be

joined together and displayed in one query, or in one report.

Personal Data Table 1 Citizenship Data Table 2

---ID Field (00000012) ---ID Field (00000012)

---First Name Field (Joe) ---Citizenship Status Field (A1)

---Last Name Field (Smith) ---Citizenship Status Descr Field

(Active)

---City Field (Princeton) ---Country of Citizenship Field (USA)

---State Field (NJ) ---Country of Citizenship

Description Field (United States

of America)

---Country Descr Field

(USA)

---Gender Field (M)


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After joining the two tables:

Joined Table 3 (Personal Data & Citizenship Data)

---ID Column

---First Name Column

---Last Name Column

---City Column---State Column

---Country Descr Column

---Gender Column

---ID Column

---Citizenship Status Column

---Citizenship Status Descr Column

---Country of Citizenship Column

--- Country of Citizenship Description Field Column

The Query behind the Joined Table 3 can be displayed as a report.

The Query for Joined Table 3 would be:

Select * from Personal_Data_Table join Citizenship Data on ID = ID;

Select all records from the Personal Data Table matching records on the ID columns.


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Join Types: Inner, Outer, Left, Right, Cartesian Product.

An INNER Join returns rows when there is at least one matching record found in both tables.

Visually, an INNER Join can be seen in through Venn diagram

Table A Table B

EmplID Country EmplID Dept

123 USA 120 HR

124 USA 121 HR

125 USA 123 HR

130 Mexico 124 HR

131 Mexico 125 HR

132 Mexico 130 Finance140 Mexico 133 Finance

Total: 7 Records 140 OIT

141 OIT

142 OIT

Total: 10 Records

Select A.Emplid, A.Dept from Table A INNER JOIN Table B on A.Emplid = B.Emplid;

This is how the Join happens

A total of 5 records will be returned because the Query only returns records which have an EmplID

in both Table A and Table B: EmplIDs 123, 124, 125, 130, 140.

Table A Table B

JoinR

esults


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An OUTER Join returns rows when there are records from Table A even if there are no matching

records in Table B (LEFT OUTER Join), or vice-versa, the OUTER Join can return rows when there are

records from Table B even if there are no matching records in Table A (RIGHT OUTER Join),.

Visually, an OUTER Join (bothLEFTand RIGHT) can be seen in through Venn diagrams

LEFT OUTER Join RIGHT OUTER Join

Table A Table B


123 USA 120 HR

124 USA 121 HR

125 USA 123 HR

130 Mexico 124 HR

131 Mexico 125 HR

132 Mexico 130 Finance

140 Mexico 133 Finance

Total: 7 Records 140 OIT

141 OIT

142 OIT

Total: 10 Records

Select A.Emplid, A.Dept from Table A OUTER JOIN Table B on A.Emplid = B.Emplid;

This is how the LEFT OUTER Join happens

Table A Table B

Join Results

Table A Table B

Join Results


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A total of 7 records will be returned because the Query only returns records which have an EmplID

and Dept from Table A which matches exactly in Table B. EmplIDs 123, 124, 125, 130, 131, 132, 140.

Query Results

EmplID Dept

123 HR

124 HR

125 HR

130 B

131 NULL (no record

of 131 in Table B)

132 NULL (no record

of 132 in Table B)

140 C

Total: 7 Records

A LEFT OUTER JOIN returns all the rows from the left table, or the first table, mentioned in the

Query, even if there are no matches in the right table (second table).

A RIGHT OUTER JOIN returns all the rows from the right table, or the second table, mentioned in the

Query, even if there are no matches in the left table (first table).


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Cartesian Production

A Cartesian product, also known as a Cross Joinis a relationship which joins each row from Table A

to each row in Table B. This happens because no relationship is defined in the Query.

Select A.EmplID, B.Dept

Notice there is no where clause to define the relationship.

If a Cartesian product, or cross join, was created between Table A and Table B below, the resulting

Table would have 70 rows.

Table A Table B


123 A 120 A

124 A 121 A

125 A 123 A

130 B 124 A

131 B 125 A

132 B 130 B

140 B 133 B

Total: 7 Records 140 C

141 C

142 C

Total: 10 Records

Query Results

EmplID Dept

123 A

123 A

123 A

123 A

123 A

123 B

123 B

123 C

123 C

123 C

124 A

124 A

124 A

124 A


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124 A

124 B

124 B

124 C

124 C

124 Cetc

Total: 70 Records


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What is Cardinality?The term cardinalityrefers to the uniqueness of data values contained in a particular column

(attribute) of a database table. The lower the cardinality, the more duplicated elements in a column.

In Report Studio, Cardinality is a visual representation of the type of Join, either Inner, Outer, Left, or

Right.

Cardinality can be expressed as:

One-to-one relationship (1:1)

One-to-many relationship (1:N)

Zero-to-one (0:1)

Zero-to-many (0:N)

A one-to-one Cardinality would look like:

Each ID record in the Personal Table has one and only one matching ID record in the Citizen

Table.

Each ID record in the Citizen Table has one and only one matching ID records in the Personal

Table.

(This is an Inner Join)


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In this join, the Cardinality is a one-to-many relationship, meaning that:

Each ID record in the Personal Table has one or more than one matching ID record,in the Citizen

Table.

Each ID record in the Citizen Table has one or more than one matching ID record in the Personal

Table.

(This is an Inner Join)


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A zero-to-one Cardinality would look like:

Each ID record in the Personal Table has zero or only one matching ID record,in the Citizen

Table.

Each ID record in the Citizen Table has zero or only one matching ID record in the Personal

Table.

(This is an Outer Join)


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A zero-to-many Cardinality would look like:

Each ID record in the Personal Table has zero or many matching ID record,in the Citizen Table.

Each ID record in the Citizen Table has zero or many matching ID record in the Personal Table.

(This is an Outer Join)


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Referring to the definition of a LEFT JOIN:

A LEFT JOINreturns all the rows from the left table, or the first table, mentioned in the Query, even

if there are no matches in the right table (second table)

A LEFT OUTER JOIN, using a zero-to-many relationship, would look like:

Each ID record in the Personal Table has zero or many matching ID record,in the Citizen Table.

Each ID record in the Citizen Table has one or many matching ID record in the Personal Table.


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Referring to the definition of a RIGHTJOIN:

A RIGHT JOINreturns all the rows from the right table, or the second table, mentioned in the

Query, even if there are no matches in the left table (first table).

A RIGHT OUTER JOIN, using a zero-to-many relationship, would look like:

Each ID record in the Personal Table has one or many matching ID record,in the Citizen Table.

Each ID record in the Citizen Table has none or many matching ID record in the Personal Table.


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Report Studio Terms

Report Studio lends the ability to create joins between Query Subjects. Usually these joins between

Query Subjects are completed using the Cognos Framework Manager tool, and are already available

to the report writer in Report Studio. However, the report writer can choose to create his own joins,

either between Query Subjects which have not been joined using the Framework Manager tool, orthose that have been joined, for which the report writer needs to enforce his own join relationship,

overriding the relationship defined in Framework Manager.

From Cognos: in general, join relationships should be created in the Framework Manager model.

Create a join relationship in Report Studio if what you are trying to do cannot be modeled in

Framework Manager.

In the Cognos 8 Training Package, none of the three available Query Subjects, Personal Data,

Citizenship Data, and Job Data, are joined to any other Query Subject. The only way to retrieve data

from more than one Query Subject into one report is to create a join between the Query Subjects.

The following four Exercises will explore the different types of Joins we can create in Report Studio.

Exercise One - Join

The Personal Data Query Subject contains data about someones address. The Job Query Subject

contacts data about someones job information. Joining the two will allow a report to be written

showing both sets of data.

We will create two queries, each one holding either a set of Personal Data columns or Job Data

columns. We will then create a join relationship, specifying a one-to-many relationship on the

EmplIDs from each field. Finally, we will then create a third query to contain both sets of columns.

Query Subjects:

1.

Personal Data containing 1059 records

2.

Job Data containing 34 records

3.

Result: 32 Records (with Auto Aggregation). 34 Records (without Auto Aggregation).


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Steps:

Create two queries.

1. Open Report Studio. Select a List type report. Save this report as Join Personal & Job Data.

2. Mouse over the Query Explorer and click on yellow Queries icon.

3. Click once on the blue Query 1 icon.

4. In the Properties area, in the Name option, rename Query1 to PersonalQuery.


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5. Double click on the PersonalQuery icon. Once inside the query, add the following columns from

the Personal Data Query Subject, found on the Source tab.

ID

Last Name

First Name Street Address 1

City

State

Postal Code


7. From the Toolbox tab, drag over a Query icon, placing below the PersonalQuery.


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8. In the Properties area, in the Name option, rename Query1 to JobQuery.

9. Double click on the JobQuery icon. Once inside the query, add the following columns from the

Job Data Query Subject, found on the Source tab.

We are ready to join both Queries.


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11. From the Toolbox tab, drag over a yellow Join icon and place it below JobQuery.

12. Drag the PersonalQuery into the first block of the Join (called a Join Operand).

13. Drag the JobQuery into the second block of the Join.

14. Double click on the Join icon. A new window will open. Here we will create the join

relationship, setting the Cardinality to a one-to-many relationship.


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15. Click the New Link button. A new link will be created between the first column listed under

each Query. (To change which columns are linked, click on the desired column name).

16. Set the Cardinality to a one-to-many relationship.

Each ID record in the Personal Table has one or many matching ID records,in the Citizen Table.

Each ID record in the Citizen Table has one or many matching ID records in the Personal Table.

17. Click OK to exit the Join Relationships window.

18. Click once on Query One found to the left of the Join icon. This is the query which is the

recipient of the joins.

19. In the Properties area, in the Name option, rename Query1 to JoinPersonJobQuery.


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20. Double-click on JoinPersonJobQuery. From the Source Tab, add the following columns from

both the PersonalQuery and JobQuery, into the Data Items section of the page:

PersonalQuery JobQuery

ID ID

Last Name Full Name

First Name Last Name

Street Address 1 First Name

City Middle Name

State Dept ID

Postal Code Dept Name

Salary

These are the fields which will be used in the PersonalJobQuery to populate the list report, on the

Report Page.

21. Mouse over the Page Explorer and click on Page1.


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22. Click anywhere on the List. In the Properties area, click up the Ancestor arrow button, and

select List. The entire List will be highlighted grey.

23. In the Properties section, in the Query area, change the Query which supplies the List to

PersonalJobQuery.


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24. From the Data Items tab, located to the right of the Source tab, add the following columns to

the List Reportfrom the JoinPersonJobQuery.

ID

Last Name

First Name Street Address 1

City

State

Postal Code

Dept ID

Dept Name

Salary

25. To set the number of rows which appear in the report on one page, click anywhere in the list. In

the Properties area, click up the Ancestor arrow button, and select List. The entire List will be

highlighted grey. In the Rows Per Page property, set the number of rows to 1500.

26. To sort records in the ID Column, click on the ID Colum, in the blue List Column Title area.

27. With the ID List Column Title area highlighted, click the Sort button. The ID Column will now

be sorted.

28. To count the number of IDs appearing in the list, click on the ID column, in the blue List Column

Title area.

29. With the ID List Column Title area highlighted, click the Aggregate Button in the toolbar, and

select Count. A new summary row should appear in the list.


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30. Run the report

Result: Notice that there are 32 rows returned, yet there are 34 rows in the Job Table, and 1059 in

the Personal Data table. The reason for this is that by default, a Join in Report Studio is an

INNER JOIN, and our Cardinality specified there should be one record.

Also, Auto Aggregation.

Finish


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Turn Auto Aggregation Off

Using the results from the Job Personal Report, in the previous Join exercise, we notice there are

32 records returned. There is only one record returned for ID #000000012, Yat-Tze Huang,

stating a Salary entry for $457,500. However, this person actually has two records in the Job

Table, each record containing a different Salary entry. The Salary column in the Job Table is anumeric field. All numeric records are Auto Aggregated in Report Studio, meaning that

multiple records for one unique ID are combined into one row. To see each record broken out,

so that in this example there would be two rows returned for Yat-Tze Huang, each one showing

the different Salary entries, the Auto Aggregation feature in Report Studio needs to be turned

off.

1. Open the previous Join Personal & Job Data report created in the Join Exercise above. Rename

it Auto Aggregation Off and save the report.

In a report which displays a list, based on the results of a Join, the auto-aggregation property is

turned off on the column in the source query, not in the resulting joined query.

2. Mouse over the Query Explorer and click on JobQuery.

3. Click once on the Salary data item.

4. In the Properties area, change the Aggregate Function Property to None.


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5. Run the report. A total of 34 records should be returned, with two Salary rows returned for ID

000000012.

Finish.


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Exercise Two - Union

A Union Join combines the records of two tables together. It is similar to a Join, but the restriction

of a Union Join is that all corresponding columns need to be of the same data type and only distinct

values are selected. Said another way, it removes duplicate rows between the various select

statements.

The Personal Data Query Subject contains data about someones address. The Citizenship Query

Subject contacts data about someones citizenship information. Joining the two will allow a report

to be written showing both sets of data.

We will create two queries, each one holding either a set of Personal Data columns or Citizenship

Data columns. We will then create a join relationship, specifying a one-to-many relationship on the

EmplIDs from each field. Finally, we will then create a third query to contain both sets of columns.

Query Subjects:

1.

Personal Data containing 1059 records

2.

Citizenship Data containing 1049 records

Exercise Three - Intersect

A Intersect Join combines the records of two queries together and returns only rows that appear in

both queries.

SELECT * FROM Table A WHERE EmplID BETWEEN 1 AND 100

INTERSECT

SELECT * FROM Table A WHERE EmplID BETWEEN 50 AND 200;


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Exercise Four - Except

An Except Join finds the distinct rows from one query and returns only those rows that do not

appear in query two.

SELECT *

FROM Table A

WHERE EmpID BETWEEN 00000001 AND 00000100

EXCEPT

SELECT *

FROM Table A

WHERE EmpID BETWEEN 00000050 AND 00000075;

Documents

Joins in report studio