The SQL Query Language: Simple SELECT Commands

The SQL Query
Language: Simple
SELECT Commands
Database Systems
9/19/24

Announcements
• Team Project
• Mid-terms
• Chapter review questions
• Question from students
• W3schools SQL Quiz

What is SQL?
• SQL stands for Structured Query Language and is a computer language that
we use to interact with a relational database.
• In a DBMS, the SQL database language is used to:
• Create the database and table structures
• Perform basic data management chores (add, delete and modify)
• Perform complex queries to transform raw data into useful information
• There are two types of SQL: data definition language (DDL) and data
manipulation language (DML)
• DDL- create the database and table structures
• DML- insert, delete, select and update data within the database tables

DDL
• The major SQL DDL statements are CREATE DATABASE and
CREATE/DROP/ALTER TABLE. The SQL statement CREATE is
used to create the database and table structures.
• CREATE: use the CREATE command to create a UNIVERSITY
database.
• CREATE DATABASE PetShop

CREATE TABLE command
• The general format for the CREATE TABLE command is:
• CREATE TABLE <tablename>
(
ColumnName, Datatype, Optional Column Constraint,
ColumnName, Datatype, Optional Column Constraint,
Optional table Constraints
);
• Optional column constraints include:
• NULL, NOT NULL, UNIQUE, PRIMARY KEY and DEFAULT

Data Type
• The data type must be a system data type or a user-defined data
type. Many of the data types have a size such as CHAR(35) or
Numeric(8,2).
• Bit –Integer data with either a 1 or 0 value
• Int –Integer (whole number) data from -2^31 (-2,147,483,648) through 2^31 – 1
(2,147,483,647)
• Smallint –Integer data from 2^15 (-32,768) through 2^15 – 1 (32,767)
• Tinyint –Integer data from 0 through 255
• Decimal –Fixed precision and scale numeric data from -10^38 -1 through 10^38
• Numeric –A synonym for decimal
• Timestamp –A database-wide unique number
• Uniqueidentifier –A globally unique identifier (GUID)
• Money – Monetary data values from -2^63 (-922,337,203,685,477.5808) through
2^63 – 1 (+922,337,203,685,477.5807), with accuracy to one-ten-thousandth of a
monetary unit
• Smallmoney –Monetary data values from -214,748.3648 through
+214,748.3647, with accuracy to one-ten-thousandth of a monetary unit

Data Types continued
• Float –Floating precision number data from -1.79E + 308 through 1.79E + 308
• Real –Floating precision number data from -3.40E + 38 through 3.40E + 38
• Datetime –Date and time data from January 1, 1753, to December 31, 9999,
with an accuracy of one-three-hundredths of a second, or 3.33 milliseconds
• Smalldatetime –Date and time data from January 1, 1900, through June 6,
2079, with an accuracy of one minute
• Char –Fixed-length non-Unicode character data with a maximum length of
8,000 characters
• Varchar –Variable-length non-Unicode data with a maximum of 8,000
characters
• Text –Variable-length non-Unicode data with a maximum length of 2^31 – 1
(2,147,483,647) characters
• Binary –Fixed-length binary data with a maximum length of 8,000 bytes
• Varbinary –Variable-length binary data with a maximum length of 8,000 bytes
• Image – Variable-length binary data with a maximum length of 2^31 – 1
(2,147,483,647) bytes

Primary Key if Composite and Foreign
Key
USE HOTEL
GO
CREATE TABLE tblRoom
(
HotelNo Int NOT NULL ,
RoomNo Int NOT NULL,
Type Char(50) NULL,
Price Money NULL,
PRIMARY KEY (HotelNo, RoomNo),
FOREIGN KEY (HotelNo) REFERENCES tblHotel
)

The SQL Query Language: Simple SELECT Commands

DML
• The SQL data manipulation language (DML) is used to query
and modify database data. In this chapter, we will describe
how to use the SELECT, INSERT, UPDATE, and DELETE SQL
DML command statements, defined below.
• SELECT – to query data in the database
• INSERT – to insert data into a table
• UPDATE – to update data in a table
• DELETE – to delete data from a table

In the SQL DML statement:
• Each clause in a statement should begin on a new line.
• The beginning of each clause should line up with the
beginning of other clauses.
• If a clause has several parts, they should appear on separate
lines and be indented under the start of the clause to show
the relationship.
• Upper case letters are used to represent reserved words.
• Lower case letters are used to represent user-defined
words.

SELECT (from a single table)
• Sample query:
SELECT student_id
FROM Enrolled
WHERE credit_status = 'grad’;
• Basic syntax:
SELECT column1, column2, …
FROM table
WHERE selection condition;
• the FROM clause specifies which table you are using
• the WHERE clause specifies which rows should be included in the result
• the SELECT clause specifies which columns should be included

SELECT (from a single table) (cont.)
• Example:
SELECT student_id
FROM Enrolled
WHERE credit_status = 'grad';

Selecting Entire Column
• If there's no WHERE clause, the result will consist of one or
more entire columns. No rows will be excluded.
SELECT student_id
FROM Enrolled;

Selecting Entire Rows
• If we want the result to include entire rows (i.e., all of the
columns), we use a * in the SELECT clause:
SELECT *
FROM Enrolled
WHERE credit_status = 'grad';

The WHERE Clause
• The selection condition must be an expression that
evaluates to either true or false.
• example: credit_status = 'grad’
• can include any column from the table(s) in the FROM clause
• The results of the SELECT command will include only those
tuples for which the selection condition evaluates to true.

Simple Comparisons
• The simplest selection condition is a comparison that uses
one of the following comparison operators:

Practice
• Write a query that finds the names and capacities of all
rooms that hold at least 70 people.

The SQL Query
Language: Simple
SELECT Commands

Why Learn SQL?
• Desktop database systems like Access provide tools for
manipulating data in a database.
• However, these tools don't allow you to perform all possible
types of queries.
• For more flexibility and power, we use SQL.
• a query language
• In addition, knowledge of SQL is needed to perform queries
from within a program.

How could we get all info about movies
released in 2010?

How could we get all info about movies
released before 2010?

How could we get the name and
runtime of movies released before
2010?

runtime of all movies?

Forming More Complex Selection
Conditions
• We often want to combine conditions or take the opposite
of one.
• SQL provides logical operators for this purpose:

Range Comparisons
• SQL also provides a special operator called BETWEEN for
checking if a value falls within a range of values.

runtime of both Titanic and Toy Story 3?

Practice with Simple SQL Queries
• Write a query that finds all information about CAS 315.
• Write a query that lists the names and start times of all
courses.
• Write a query that gets the ID numbers of student(s) who
are taking CS 105 for undergraduate (ugrad) credit.

The SQL Query Language: Simple SELECT Commands

Recommended

More Related Content

Similar to The SQL Query Language: Simple SELECT Commands (20)

Recently uploaded (20)

The SQL Query Language: Simple SELECT Commands