IS6126 Databases for Management
Information Systems
Lecture 2: SQL II – Joins, Updates,
Insertions, and Deletions
Rob Gleasure
[email protected]
robgleasure.com
IS6126
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Today’s session
 More SQL
 Insert Into
 Update
 Delete
 Joins
 Exercise
More on the SQL DML
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So far we’ve looked at getting data from specific tables, but there
are still two parts of the Data Manipulation Language (DML) we
haven’t covered
The DML has four main elements
 Select
 Insert Into
 Update
 Delete
Also, what if our data isn’t on one table?…
Insert Into
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We use INSERT INTO queries to add new tuples (aka records,
rows) into a table
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The basic structure of an INSERT-INTO query is as follows
INSERT INTO
table_name1 (column_name1, column_name2, …)
VALUES
value1, value2, …;
Insert Into
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For example, say we want to insert a new student in a Students
table with a Student_ID of 12345678 and a Name of “Jane Smith”,
we might have the following
INSERT INTO Students (Student_ID, Name) VALUES (12345678, “Jane Smith”) ;
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Note that we insert the data in the form of a new tuple (aka record,
row) and if we do not specify a column, we have to provide data for
each column in the new record
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Example
http://www.w3schools.com/sql/trysql.asp?filename=trysql_insert_cols
Update
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We use UPDATE queries to modify existing tuples (aka records,
rows) in a table
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The basic structure of an UPDATE query is as follows
UPDATE
table_name1, table_name2, …
SET
col_name1 = value1, col_name2 = value2, …;
WHERE
some_column=some_value;
Update
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For example, say we want to change the previously added student
record to be “Janet Smith”, we might have the following
UPDATE Students SET (Name = “Janet Smith”) WHERE (Student_ID=12345678) ;
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Careful with this, if you don’t set a WHERE condition you will
change every record in the database
Example
http://www.w3schools.com/sql/trysql.asp?filename=trysql_update
Delete
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We use DELETE queries to remove existing tuples (aka records,
rows) in a table
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The basic structure of a DELETE query is as follows
DELETE FROM
table_name
WHERE
some_column=some_value;
Delete
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For example, say we want to delete the previously added student
record, we might have the following
DELETE FROM Students WHERE (Name = “Janet Smith”);
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Again – be careful, if you don’t set a WHERE condition you delete
every record in the database
Example
http://www.w3schools.com/sql/trysql.asp?filename=trysql_delete
Joins
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Joins combine tuples (aka rows, records) from multiple tables
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Joins come in several forms
 Inner Joins
 Left Joins
 Right Joins
 Full Joins
 Unions
 Select Into/Into Select
Inner Joins
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Inner Joins return the specified columns at the intersection of two or
more tables
Image from http://www.w3schools.com/
Inner Joins
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Inner Joins are the most basic (and probably most common) type of
join
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The basic structure of an INNER JOIN query is as follows
SELECT
column_name(s)
FROM
table1
INNER JOIN
table2
ON
table1.column_name=table2.column_name;
Inner Joins
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For example, say in addition to the previously added student record,
a separate REFERENCES table stores student details. We could
retrieve Student_IDs included in both tables as follows:
SELECT Students.Student_ID, Student.Name, References.Ref_Details
FROM Students INNER JOIN References
ON Students.Student_ID = References.Student_ID;
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Example
http://www.w3schools.com/sql/trysql.asp?filename=trysql_select_join_inner
Left Joins
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Left Joins (sometimes called left outer joins) return all of the
specified columns from the first table and their intersection (where it
exists) with two or more tables
Image from http://www.w3schools.com/
Left Joins
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The big difference here is that columns from our first table that have
no corresponding entry in the latter tables are still returned (with null
signifying the missing entry)
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The basic structure of an LEFT JOIN query is as follows
SELECT
column_name(s)
FROM
table1
LEFT JOIN
table2
ON
table1.column_name=table2.column_name;
Left Joins
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For example, what if some students do not have references and we
still want to see their Student_ID and Name? We could retrieve
these records as follows:
SELECT Students.Student_ID, Student.Name, References.Ref_Details
FROM Students LEFTJOIN References
ON Students.Student_ID = References.Student_ID;
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Example
http://www.w3schools.com/sql/trysql.asp?filename=trysql_select_join_left
Right Joins
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Right Joins (sometimes called right outer joins) return all of the
specified columns from the latter tables and their intersection (where
it exists) with the first table
Image from http://www.w3schools.com/
Right Joins
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Here, columns from our latter tables that have no corresponding
entry in the first tables are still returned (with null signifying the
missing entry in the first table)
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The basic structure of an RIGHT JOIN query is as follows
SELECT
column_name(s)
FROM
table1
RIGHT JOIN
table2
ON
table1.column_name=table2.column_name;
Right Joins
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For example, what if some references have been received before
the corresponding student records have been created and we still
want to see them? We could retrieve these records as follows:
SELECT Students.Student_ID, Student.Name, References.Ref_Details
FROM Students RIGHT JOIN References
ON Students.Student_ID = References.Student_ID;
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Example
http://www.w3schools.com/sql/trysql.asp?filename=trysql_select_join_right&
ss=-1
Full Outer Joins
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Full Outer Joins return all of the specified columns from the first and
latter tables, including entries in either table with no corresponding
table in the other(s)
Image from http://www.w3schools.com/
Full Outer Joins
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Here, columns from our any table that have no corresponding entry
in other tables are still returned (with null signifying the missing
entry)
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The basic structure of an FULL OUTER JOIN query is as follows
SELECT
column_name(s)
FROM
table1
FULL OUTER JOIN
table2
ON
table1.column_name=table2.column_name;
Full Outer Joins
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For example, what if we want to see the full set of records to
determine which student records we have not yet created and which
references are still outstanding? We could retrieve these records as
follows:
SELECT Students.Student_ID, Student.Name, References.Ref_Details
FROM Students FULL OUTER JOIN References
ON Students.Student_ID = References.Student_ID;
Unions
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Unions are a bit different, they tend to be used for retrieving
comprehensive sets of similar records
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Unions combine two or more SELECT queries, provided the
following conditions are met
 Each SELECT query must have the same number of columns
 Each merged column must share data types
 Columns in each SELECT query must be in the same order
Unions
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The basic structure of a UNION query is as follows
SELECT
column_name(s)
FROM
table1
UNION
SELECT
column_name(s)
FROM
table2;
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Note that this will automatically return only distinct records, though
we can used UNION ALL if we want to include duplicates
Unions
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For example, what if our students table only stores enrolled
students, whereas another Provisional_Students table stores
students in provisional places awaiting confirmation? We could
retrieve these records as follows:
SELECT Name FROM Students
UNION
SELECT Name FROM Provisional_Students
ORDER BY Name;
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Example
http://www.w3schools.com/sql/trysql.asp?filename=trysql_select_union_all2
Select Into
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Sometimes we want to copy an entire schema into a new table. We
can do this using SELECT INTO as follows
SELECT
column_name(s)
INTO
newtable
FROM
table1;
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This often ends up as a way of backing things up, e.g.
SELECT * INTO Students_Backup FROM Students
Insert Into Select
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Alternatively, sometimes we want to add data from one table to an
existing table. We can do this using INSERT INTO SELECT as
follows
INSERT INTO
table2 (column_name(s))
SELECT
column_name(s)
FROM
table1;
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Example
http://www.w3schools.com/sql/trysql.asp?filename=trysql_insert_into_select
Exercise
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1.
2.
Consider the following problems related to the Customers database,
what queries best solve them?
We want to retrieve all customers with addresses in Mexico?
We want to add a new Customer called 'Juan Garcia Ramos', with
contact name 'Juan Ramos', address of 'Tribulete 4356', in the city
'México D.F', with a post code of '05029', in the country of 'Mexico‘?
3.
We want to update that customer’s contact name to ‘Anna Ramos’?
4.
We want to delete the same customer?
Exercise
5.
We want to select ProductName and CategoryID from the Products
table, along with the SupplierName from the Suppliers table using a
left join. Hint: use the SupplierID column in the Products table as a
foreign key
6.
We want to retrieve all cities mentioned in customer records and
supplier records using a union
7.
We want create e new Customer_Cities_Backup table storing all
cities listed in the Customers table
8.
We want to add all cities listed in the Suppliers table into the
Customers table