SQL Review

Tonga Institute of Higher Education

SQL Introduction SQL (Structured Query Language) a language

that allows a developer to work with data in a database.

This presentation serves to provide a basic review of SQL statements. Advanced concepts are covered in IT244 – Database Management Systems

All examples will use the Northwind Access database. This database is available from www.microsoft.com.

Working with Data in a Database

SQL answers 4 common questions:

How do I get data from a database? SELECT How do I add new data to a database? INSERT How do I change data in a database? UPDATE How do I delete data from a database? DELETE

SELECT Statement Basics

How do I get data from a database? Use SELECT!

SELECT <Column Names> FROM <Table Name> WHERE <Criteria>

Returns data from the columns of the rows that match the criteria.

SELECT Column Names

Specify the column names that you wish to receive data from.

Multiple column names should be separated by commas. SELECT CompanyName, ContactName, Phone FROM

Customers An asterick (*) can be used to get data from all the

columns. SELECT * From Customers

SELECT Criteria

Criteria can be added to get specific rows of data. For example, this code returns rows that include

CompanyNames from Customers that have a contact name Maria.

SELECT CompanyName FROM Customers WHERE ContactName = ‘Maria’

In this case, nothing is returned because there is no customer with the Contact Name of exactly ‘Maria’

SELECT Criteria Wildcards Criteria wildcards can be used to

find rows that contains certain pieces of data.

For example, this code returns all CompanyNames from Customers that INCLUDE a contact name Maria.

SELECT CompanyName FROM Customers WHERE ContactName like ‘%Maria%’

Returns 2 rows both include Maria in the ContactName column.

Any characters can be after Maria

Any characters can be before Maria

Often % is used for wildcardsSometimes * is used for wildcards

SELECT Summary

Using the SELECT statement, we can query our database.

For example, to get all the column data from all rows with a contact name that includes Maria, use this code:

SELECT * FROM Customers WHERE ContactName like ‘%Maria%’

Comprehension Check

SELECT Statement

INSERT Statement Basics

How do I add new data to a database? Use INSERT!

INSERT INTO <Table Name> (<Column Names>) VALUES (<Data>)

Inserts a new row with data in the columns specified.

INSERT Data

INSERT INTO Customers (CustomerID, CompanyName) VALUES (‘TICO’, ‘Ti Company and Associates’)

Each column name to the left of VALUES matches a piece of data to the right.

Use commas to separate each column name and piece of data.

String require single quotes. Sometimes, double quotes may be used.

Make sure you insert data for required columns.

INSERT Summary

Using the INSERT statement, we can insert new rows into our database.

For example, to add a new customer with the ID TICO and name of Ti Company and Associates, use this code:

INSERT INTO Customers (CustomerID, CompanyName) VALUES (‘TICO’, ‘Ti Company and Associates’)

Comprehension Check

INSERT Statement

UPDATE Statement Basics

How do I change data in a database? Use UPDATE!

UPDATE <Table Name> SET <Column Name> = ‘<New Value>’ WHERE <Criteria>

Updates rows that match the criteria by changing the data in the columns specified to the new value.

UPDATE Details

UPDATE Customers SET ContactName = ‘Sione Tukuia’, Phone = ‘13533’ WHERE CustomerID = ‘ANATR’

Use commas to separate each data update. String require single quotes. Sometimes, double

quotes may be used. Make sure the criteria is correct. If no criteria is

included, then all data will be updated.

UPDATE Summary

Using the UPDATE statement, we can update data in our database.

For example, to change the contact name and phone number of the customer with ID ANATR, use the following code:

UPDATE Customers SET ContactName = ‘Sione Tukuia’, Phone = ‘13533’ WHERE CustomerID = ‘ANATR’

Comprehension Check

UPDATE Statement

DELETE Statement Basics

How do I delete data from a database? Use DELETE!

DELETE FROM <Table Name> WHERE <Criteria>

Deletes rows that match the criteria.

DELETE FROM Customers WHERE ContactName like ‘%Maria%’

DELETE Details

DELETE FROM Customers WHERE CustomerID = ‘ANATR’

Make sure the criteria is correct. If no criteria is included, then all data will be deleted.

DELETE Summary

Using the DELETE statement, we can delete data in our database.

For example, to delete the customer with ID ‘ANATR’, use the following code:

DELETE FROM Customers WHERE CustomerID = ‘ANATR’

Comprehension Check

DELETE Statement