Sq lite module7

MODULE 7: WORKING WITH MULTIPLE
TABLES
SQL and Scripting Training
(C) 2020-2021 Highervista, LLC 1

2
TOPICS
Introduction to Joins
Joins and the relational database
structure
Joins and aliases
Inner join, left outer join, and right outer
join
Joining more than two tables
Adding calculations to queries
Types of functions in SQL
String functions
Date functions
Aggregate functions
Using the WHERE and HAVING clauses
with functions
Grouping by multiple columnssubqueries
and aggregate functions
SELECT statement subqueries
WHERE clause subqueries
Summary

INTRODUCTION TO JOINS
SQL and Scripting
Training

5
A JOIN is a command that combines fields in two or more tables of a relational database.
As an example: For the sTunes database, it would be logical to query fields from both the
Invoices and Customers tables, since customers can have invoices.

6
Since CustomerId is the primary key of the Customers table and there is a similar field of the
same name in the Invoices table, there is a linkage between these two tables.
Both tables can be merged on the CustomerId field for each.
Note: This type of join is called
an INNER JOIN. We′ll discuss
other types of joins.

7
The query begins with a SELECT * (for
all fields). This will provide fields from
both tables (22 total fields).
The ON keyword provides the linkage
between the two tables. The resulting
table looks like this:

JOINS AND THE RELATIONAL
DATABASE STRUCTURE
SQL and Scripting
Training

9
HOW JOINS INTERACT WITH THE RELATIONAL
DATABASE STRUCTURE
When examining the output from the prior Join command, you can see a repeating set of
information for customer 1 (Luis).
Looking back at an ERD, you can say that this customer (Luis) has a 1:M relationship with the
Invoices table.
Let′s examine the ERD for the sTunes db. Note that the ERD is in an MS/Access type of ERD
notation.

11
STUNES ERD
The database is normalized (through 3NF).
Examine the linkages between tables (PK to FK).
As noted earlier, the relationship between each pair of tables is bidirectional. It can be
read in either direction.

12
USING JOINS WITH AN ALIAS
Since two tables in any given database may have fields with identical names,
when creating joins it is necessary to specify the table name with the associated
field name.
Aliases reduce the amount of typing required and serve to help readability.

13
IDENTICAL JOINS
SELECT
*
FROM
invoices
INNER JOIN
customers
ON
invoices.CustomerID =
customers.CustomerID
SELECT
*
FROM
Invoices AS i
INNER JOIN
Customers AS c
ON
i.CustomerID = c.CustomerID

14
USING ALIASES WITH FIELD NAMES:
EXAMPLE
SELECT
c.LastName,
c.FirstName,
i.InvoiceID,
i.CustomerID,
i.InvoiceDate,
i.Total
FROM
invoices AS i
INNER JOIN
customers AS c
ON
i.CustomerId = c.CustomerID
ORDER BY
c.Lastname

15
USING ALIASES WITH FIELD NAMES:
RESULTS

16
JOIN TYPES AND THEIR DIFFERENCES
What happens if the data from the tables joined doesn’t match up?
For example, suppose a customer deleted his customer database record (removing his record from the
Customers table).
Because the company is required to keep financial records, the invoices for the customer were not deleted.
It is not unusual to find discrepancies in databases, and you must decide whether queries should include or
exclude data that does not match up.

17
EXAMPLE TABLES (NOT THE STUNES DB)
Discrepancies
1. Invoices table shows someone with a
customer ID of 6 who made a purchase
on 5/1/2017, but this customer does not
show up on the Customers table.
2. It appears that customer ID 1 and
customer ID 5 (on the Customers table)
never made a purchase (they’re not on
the Invoices table).
3. We’ll look at how this is handled with
various JOIN types.

18
INNER JOIN: HOW ARE DISCREPANCIES HANDLED?
Inner Join—Only returns matching records. Any unmatched data from either table is
ignored.

19
Note: In this example, the Inner Join
will join four common records.

20
SELECT
i.InvoiceId,
c.CustomerId,
c.LastName,
c.Address,
i.InvoiceDate,
i.BillingAddress,
i.total
FROM
invoices AS i
INNER JOIN
customers AS c
ON
i.CustomerId = c.CustomerId

21
LEFT OUTER JOIN: HOW ARE DISCREPANCIES
HANDLED?
Note: The concept of a left table and a
right table depends entirely on the order
that tables are listed in the JOIN
statement.

22
HANDLED?
Note: With the LEFT OUTER JOIN, everything in the Invoices table will be
displayed. Only common records in the Customers table will be displayed.

23
HANDLED?
Can you think of a business case for
displaying all invoices and only
customer data related to invoices?
SELECT
i.InvoiceId,
c.CustomerId,
c.Name,
c.Address,
i.InvoiceDate,
i.BillingAddress,
i.Total
FROM
invoices AS i
LEFT OUTER JOIN
customers AS c
ON

24
JOIN INVOICES AND
CUSTOMERS TABLE

25
RIGHT OUTER JOIN: HOW ARE DISCREPANCIES
HANDLED?
Note: For LEFT OUTER JOIN or
RIGHT OUTER JOIN, you can use
LEFT JOIN or RIGHT JOIN (same
results).
Note: RIGHT OUTER JOINs are not supported in SQLite

26
RIGHT OUTER JOIN: HOW ARE DISCREPANCIES
HANDLED?
Note: With the RIGHT OUTER JOIN, everything in the Customers table
will be displayed. Only common records in the invoices table will be
displayed.

27
HANDLED?
Can you think of a business case for
displaying all customers and only invoice
data related to customers?
SELECT
i.InvoiceId,
c.CustomerId,
c.Name,
c.Address,
i.InvoiceDate,
i.BillingAddress,
i.Total
FROM
invoices AS i
RIGHT OUTER JOIN
customers AS c
ON

28
INNER JOINS WITH MORE THAN TWO
TABLES
Joins can combine two or more tables.
Adding additional tables using joins is straightforward: It follows the same pattern as inner
joins.
Review database schema on next slide: There is a relationship between Invoices, Customers,
and Employee tables.
Note: Look at SupportRepId field (Customers table) and the EmployeeId field (Employees table).

29
TABLES
The Invoices table is
related to the Customers
table (bidirectional
relationship).
The Customers table is
related to the Employees
table (bidirectional
relationship).

30
TABLES
When using two or more
tables in a Join, think
about the fields that you
need from each table.

31
TABLES SELECT
e.FirstName,
e.LastName
e.EmployeeId,
c.FirstName,
c.LastName,
c.SupportRepID,
i.CustomerId,
i.Total
FROM
invoices AS i
INNER JOIN
customers AS c
ON
INNER JOIN
employees AS e
ON
c.SupportRepId = e.EmployeeId
ORDER BY
i.Total DESC
LIMIT 10

32
INNER JOINS WITH
MORE THAN TWO
TABLES

33
SQL
SELECT
e.FirstName,
e.LastName,
e.EmployeeId,
c.FirstName,
c.LastName,
c.SupportRepId,
i.CustomerId,
i.Total
FROM
invoices AS i
INNER JOIN
customers AS c
ON
INNER JOIN
employees AS e
ON
c.SupportRepId = e.EmployeeId
ORDER BY
i.Total DESC
LIMIT 10

34
USING LEFT OUTER JOINS WITH NULL, IS, AND
NOT
Left Outer Join—shows everything from the left table and all matching information from the
right table.
When looking at the artists and albums tables in the sTunes database, if you want to
generate a list of all artists who do not have an album, what is the process?

35
USING LEFT OUTER JOINS WITH NULL, IS, AND
NOT
A Left Outer Join provides a list of all artists along with any associated albums for artists
with albums.
The Left Outer Join will fill in any fields that do not have album titles with NULL values.

36
USING LEFT OUTER JOINS WITH NULL, IS,
AND NOT SELECT
ar.ArtistId AS [ArtistId From Artist Table],
al.ArtistId AS [ArtistId From Albums Table],
ar.Name AS [Artist Name],
al.Title AS [Album Title]
FROM
artists AS ar
LEFT OUTER JOIN
albums AS al
ON
ar.ArtistId = al.ArtistId

37
AND NOT
SELECT
al.ArtistId AS [ArtistId From Albums
Table],
FROM
artists AS ar
LEFT OUTER JOIN
albums AS al
ON
Note: The result will include artists with albums and artist without
albums (NULL).

38
AND NOT SELECT
al.ArtistId AS [ArtistId From Albums
Table],
FROM
artists AS ar
LEFT OUTER JOIN
albums AS al
ON
WHERE
al.ArtistId IS NULL
Note: To generate a report that shows artists who
do not have albums (IS NULL), include a
comparison statement where the ArtistId on the
Albums table is NULL.
Use (NOT NULL) to return only values
that were not NULL.

39
TURNING A RIGHT JOIN INTO A LEFT
JOIN
Since RIGHT OUTER JOINS are not supported in SQLite, keep in mind that:

40
DAY 7, ASSIGNMENT 2: IDENTIFY PK, FK,
CREATE INNER JOIN
Use
Using the Genres table, create a third inner
join to include the Name field from the table
in your result set.
Create
Create an inner join between the Albums and
Tracks tables and display the album names and
track names in a single result set.
Identify Identify PKs and FKs in other tables that are
associated to the Tracks table.
Use Using the sTunes ERD, view the Tracks table.

ADDING CALCULATIONS TO
QUERIES
SQL and Scripting
Training

42
ADDING CALCULATIONS TO QUERIES
Calculations, like counting the number of records returned, can be performed by
adding functions to queries.
The function COUNT ( ) can count a given field, like LastName. You can put the results
in a temporary field such as NameCount.
SELECT
COUNT (LastName) AS [NameCount]
FROM
customers
WHERE
LastName LIKE ‘B%’

TYPES OF FUNCTIONS IN SQL
SQL and Scripting
Training

44
FUNCTIONS IN SQL
Functions are special keywords that accept certain parameters,
perform an operation (such as a calculation or modification of the
data in a field), and return the result of that operation as a value.
There is a list of all SQLite functions on the SQLite website.
Note: Other DBMSs may have an extended set of
functions.

45
FUNCTIONS
• String functions modify
character and text-based
data.
• Date functions modify time
and date data.
• Aggregate functions
perform mathematical
operations.

46
FUNCTIONS
• Functions in SQL operate similarly to the way functions operate
in a spreadsheet.
• If you’ve ever used Excel functions, there is a ″pop-up″ style
definitions box that prompts the user for parameters.
• In SQL, you will need to supply the parameters when calling the
function.

STRING FUNCTIONS
SQL and Scripting
Training

48
STRING FUNCTIONS: EXAMPLE
Note: NVARCHAR is a variable character data format.
The following query would return all names with mailing addresses in the United States:
SELECT
FirstName,
LastName,
Address
FROM
customers
WHERE
Country = ‘USA’
Problem: Name data is split into parts in the database.

49
CONCATENATING STRINGS OF TEXT
Joining fields is known as concatenation.
To add two fields together, use the double pipe symbol ||
For example:
SELECT
FirstName || LastName
FROM
customers
WHERE
CustomerId = 1

50
CONCATENATING STRINGS OF TEXT
Another example:SELECT
FirstName,
LastName,
FirstName || ‘ ‘ || LastName
FROM
customers
WHERE
Country = “USA”

51
USING MULTIPLE CONCATENATIONS
Using multiple concatenations, you can create a one-line name and address list for all
customers.
SELECT
FirstName || ‘ ‘ || LastName || ‘
‘ || Address || ‘, ‘ || City || ‘, ‘ || State || ‘
‘ || PostalCode AS [MainlingAddress}
FROM
customers
WHERE
Country = “USA”

52
TRUNCATING TEXT
You can separate or truncate text to create more uniformity in the
output.
Remember that users can input inconsistencies or errors in database
fields. Using truncation is one tool to clean up how data looks in
reports.
You can use LENGTH ( ) to examine how a given value was entered in
a field.
SELECT
PostalCode,
LENGTH(PostalCode) AS [Postal
Code Length]
FROM
customers
WHERE
Country = “USA”

53
TRUNCATING TEXT
Since there are different sizes in the field, you can use another function SUBSTR() to
substring the field value and place the output on the report.
More detail on the SUBSTR ( ) function:

54
TRUNCATING TEXT: POSTAL CODE
SELECT
PostalCode,
SUBSTR(PostalCode, 1, 5) AS [Five Digit Postal Code]
FROM
customers
WHERE
Country = “USA”

55
MORE STRING FUNCTIONS: UPPER( ) AND
LOWER( )

56
UPPER AND LOWER EXAMPLE
SELECT
FirstName as [First Name Unmodified],
UPPER(FirstName) as [First Name in UPPERCASE],
LOWER(FirstName) as [First Name in lowercase],
UPPER(FirstName) || ‘ ‘ || UPPER(LastName) AS [Full Name in
UPPERCASE]
FROM
customers

DATE FUNCTIONS
SQL and Scripting
Training

58
DATE FUNCTIONS
Date functions allow you to
manipulate data stored in various
date and time formats.
In sTunes, date information is stored
in DATETIME format: YYYY-MM-DD
HH:MM:SS
All timecodes not being used are
stored as 00:00:00
Two date functions (out of several)

59
STRFTIME FUNCTION—ARGUMENTS IN ORDER:
FORMAT, TIMESTRING, MODIFIER (OPTIONAL)

60
STRFTIME FUNCTION—ARGUMENTS IN ORDER:
FORMAT, TIMESTRING, MODIFIER (OPTIONAL)

61
STRFTIME FUNCTION—ARGUMENTS IN
ORDER: FORMAT, TIMESTRING, MODIFIER
(OPTIONAL)

62
STRFTIME EXAMPLE
SELECT
STRFTIME(‘The Year is: %Y The Day
is: %d The Month is %m’, ‘2011-05-22’)
AS [Text with Conversion Specifications]

63
STRFTIME EXAMPLE—CALCULATE EMPLOYEE′S
AGE
SELECT
LastName,
FirstName,
STRFTIME(‘%Y-%m-%d’,BirthDate) AS
[Birthday No Timecode],
STRFTIME(‘%Y-%m-%d’,’now’) –
STRFTIME(‘%Y-%m-%d’, BirthDate) AS [Age]
FROM
employees
ORDER BY
Age

AGGREGATE FUNCTIONS
SQL and Scripting
Training

65
AGGREGATE FUNCTIONS
Aggregate functions can turn a
range of numbers into a single
data point based on a variety of
mathematical functions.
Previously, we used the COUNT (
) function to find the total number
of customers.
Additional aggregate functions
(not a complete list):

66
AGGREGATE FUNCTIONS: EXAMPLE
SELECT
SUM(Total) AS TotalSales,
AVG(Total) AS AverageSales,
MAX(Total) AS MaximumSale,
MIN(Total) AS MinSale,
COUNT(*) AS SalesCount
FROM
invoices

67
NESTING FUNCTIONS WITH THE ROUND (
) FUNCTION
A nested function is a function contained within another function.
One reason that you want to nest functions is to further modify the format of the inner
function.
For example, if you use the AVG ( ) function, you will see too many decimal places. You
can use the ROUND ( ) function to limit the number of decimal places.

68
NESTING FUNCTIONS WITH THE ROUND (
) FUNCTION
SELECT
AVG (Total) AS [Average Sales],
ROUND(AVG(Total), 2) AS [Rounded Average Sales]
FROM
invoices
Note: When using the ROUND ( )
function with monetary values, be
careful of rounding up, since this may
change intermediary calculations!

USING THE WHERE AND HAVING
CLAUSES WITH FUNCTIONS
SQL and Scripting
Training

70
USING AGGREGATE FUNCTIONS WITH THE
GROUP BY CLAUSE
A useful feature of aggregate functions is their ability to calculate subtotals or
aggregates for different groups of data.
SELECT
BillingCity,
AVG(Total)
FROM
invoices
ORDER BY
BillingCity
Something is wrong!?!?

71
USING AGGREGATE FUNCTIONS WITH THE
GROUP BY CLAUSE
Incorrect: A global average of all cities is calculated and ′Delhi′ is the first in the db.
To correct, you need a GROUP BY clause.
SELECT
BillingCity,
AVG(Total)
FROM
invoices
GROUP BY
BillingCity
ORDER BY
BillingCity

72
HAVING CLAUSES WITH GROUPED QUERIES
Adding criteria to a grouped query works like previous queries.
The WHERE clause allows you to add new criteria.

73
AGGREGATE FUNCTIONS: IDENTIFYING AN
ERROR
SELECT
BillingCity,
AVG(Total)
FROM
invoices
WHERE
AVG(Total) > 5
GROUP BY
BillingCity
ORDER BY
BillingCity
Note the following error message from this query:
Misuse of aggregate: AVG():
We cannot use the WHERE clause to create a
condition based on an aggregate function. The
WHERE clause can only direct the query about
what information to pull from the fields in our
SELECT clause. If you want additional filtering
based on aggregate functions, use the HAVING
clause.

74
AGGREGATE FUNCTIONS: CORRECTING AN
ERROR
SELECT
BillingCity,
AVG(Total)
FROM
invoices
GROUP BY
BillingCity
HAVING
AVG(Total) > 5
ORDER BY
BillingCity
SELECT
BillingCity,
AVG(Total)
FROM
invoices
WHERE
AVG(Total) > 5
GROUP BY
BillingCity
ORDER BY
BillingCity
Note: With a GROUP BY clause,
you must use HAVING, or you will
get an error.

75
WHERE VS. HAVING
The WHERE clause is for filtering non-aggregate data. The WHERE
clause tells the query what information to include from the table.
The HAVING clause is for filtering results containing aggregates. The
HAVING clause acts as a further filter following the WHERE.

76
WHERE VS. HAVING: EXAMPLE
SELECT
BillingCity,
AVG(Total)
FROM
invoices
WHERE
BillingCity LIKE ‘B%’
GROUP BY
BillingCIty
HAVING
AVG(Total) > 5
ORDER BY
BillingCIty

GROUPING BY MULTIPLE
COLUMNS
SQL and Scripting
Training

78
USING GROUP BY WITH MULTIPLE FIELDS
It is possible to group by more than one aggregate field at a time.
In the following example, data are grouped first by country and then by
city.

79
USING GROUP BY WITH MULTIPLE FIELDS:
EXAMPLE
SELECT
BillingCountry
BillingCity,
AVG(Total)
FROM
invoices
GROUP BY
BillingCountry, BillingCIty
HAVING
AVG(Total) > 5
ORDER BY
BillingCIty
Note: Database files are likely to contain
spelling errors.

80
SUBQUERY
A subquery is one query nested inside of another query, usually in the
SELECT, FROM, or WHERE clause.
Subqueries are useful when the query you want to create requires a few
more steps or calculations to produce the required dataset.
Instead of writing one query and copying the results to another one, you
can use a subquery to perform both operations.

81
INTRODUCTION TO SUBQUERIES
SELECT
ROUND (AVG (Total), 2) AS [Average Total]
FROM
invoices

82
INTRODUCTION TO SUBQUERIES USING AGGREGATE FUNCTIONS
SELECT
InvoiceDate,
BillingAddress,
BillingCity,
Total
FROM
invoices
WHERE Total <
(
select
AVG (Total)
from
invoices)
ORDER BY
Total DESC
Scenario: From sTunes, gather data about all invoices
that are lower than the average. Show InvoiceDate,
BillingAddress, BillingCity, and Total.

83
USING A SUBQUERY IN THE SELECT STATEMENT
SELECT
BillingCity,
AVG(Total) AS [City Average],
FROM
invoices
select
AVG (Total)
from
invoices)
FROM
invoices
GROUP BY
BillingCity
ORDER BY
BillingCity

WHERE CLAUSE SUBQUERIES
SQL and Scripting
Training

85
USING A WHERE CLAUSE IN A SUBQUERY
Our outer query can have a WHERE clause which, in turn, contains a
subquery with its own WHERE clause.
For example, if you want to find the all-time largest sale from the
dataset (records between the years of 2009-2012) and see if there are
any invoice totals in the latest year of the records (2013) that are higher
than that value (in the range 2009-2012), you would first have to get
the largest sale prior to 2013. This is done in the next example.

86
SELECT
MAX(Total)
FROM
invoices
WHERE
InvoiceDate < ‘2013-01-01’
Note: An initial look at the MAX(Total), largest sale, from years < 2013.

87
SELECT
InvoiceDate,
BillingCity,
Total
FROM
invoices
WHERE
InvoiceDate >= ‘2013-01-01’AND total >
(select
max(Total)
from
invoices
where
InvoiceDate < ‘2013-01-01’)
Note: You can build out the query by wrapping the MAX(Total) query in parentheses and write the
outer query.

88
SUMMARY
Joins harness the power of a relational database to bring data together from different tables.
Use of an entity relationship diagram is helpful when writing joins.
When selecting fields from multiple tables at once, aliases are needed to specify the table of origin.
Inner joins do not include rows where there is no corresponding data
Outer joins include all rows of one table, even when there is no corresponding data between tables. Rows that do not
match show up as NULL.
The IS and NOT keywords must be used to test for NULL values.
Right joins can be used in implementations of SQL but are not available in SQLite. To do the equivalent of a right join
in SQLite, simply switch the position of the two tables you are comparing in your query statement.

89
SUMMARY
Functions allow you to alter, reformat, and perform calculations on the data in your tables.
Queries containing numerical data can be manipulated with arithmetic operations and aggregate functions
Queries containing text can be split, concatenated, capitalized, etc.
Once data is aggregated with functions, it can be further sorted by the GROUP BY and HAVING Clauses.
The HAVING Clause does for aggregate fields what the WHERE clause does for non-aggregate fields.
The HAVING clause can be used in a query only if a GROUP BY clause is also present.
You can use GROUP BY with multiple fields to further narrow down your aggregated data.

90
SUMMARY
Subqueries allow you to execute multiple SQL statements within a single query.
Subqueries are comprised of two or more separate SQL statements identified as
inner and outer queries.
Subqueries are usually used to compare existing data with data you derive with
aggregates or other functions
The DISTINCT keyword allows you to ignore redundant data in records and
search for unique instances only.

91
REFERENCES
Allen, G., & Owens, M. (2010). The definitive guide to SQLite. Apress. (PDF)
Shields, W. (2019). Sql quickstart guide: the simplified beginner's guide to managing, analyzing,
and manipulating data with Sql. Clydebank Media.
Tutorialspoint SQLite: https://www.tutorialspoint.com/sqlite/index.htm

92
INTRODUCTION
Ron McFarland
Technologist, Educator
Source: Microsoft Images

93
ABOUT THIS COURSE
This course is distributed free. I use several
sources. But importantly, I use the book noted
on the next slide.
If you are using these PowerPoints, please
attribute Highervista, LLC and me (Ron
McFarland). IN ADDITION, please attribute
the author noted on the next slide, as the
author’s textbook provides essential
information for this course.
Source: Microsoft Images

94
INTRODUCTION
This course is offered to you free. HOWEVER, please
purchase the following book, as it is a primary resource for
this course. I do not make any $ from this course or this
book. So, since a handful of good content is derived from the
following text, please support this author!
Title: SQL Quickstart Guide
Author: Walter Shields
Available: Amazon, B&N, and through ClydeBank media
website at:
https://www.clydebankmedia.com/books/programming-
tech/sql-quickstart-guide

Sq lite module7

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Sq lite module7

Similar to Sq lite module7 (20)

More from Highervista

More from Highervista (10)

Recently uploaded

Recently uploaded (20)

Sq lite module7