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Basic SQL

ITCS 201 Web Programming Part II

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ITCS201 Web Programming, The Faculty of Information and Communication Technology, Mahidol University

Outline for Today

What is SQL?

SQL Category

Basic DML Commands

INSERT

UPDATE

DELETE

SELECT

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ITCS201 Web Programming, The Faculty of Information and Communication Technology, Mahidol University

What is SQL?

SQL Structured Query Language

Language that defines commands for user to

Create database and table structure

Basic data management

Query useful information

Not case-sensitive

Non procedural language : users specify what must be done, NOT

how it is to be done

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SQL Categories

Two broad type1. Data Definition Language (DDL) NOT Study in this course

Commands used to create database objects including

Database

Table/Attributes

Keys etc.

2. Data Manipulation Language (DML)

Commands used to insert, update, delete, and retrieve datawithin tables.

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Basic DML Commands

Commands DescriptionINSERT Insert row(s) into a table

UPDATE Modify an attributes value in one or more tables rows

DELETE Delete one or more rows from a table

SELECTSelect attributes from rows in one or more tables

WHERE Restrict the selection of rows based on condition expression

GROUP BY Group the selected rows based on one or more attributes

HAVING Restrict the selection of group rows based on a condition

ORDER BY Order the selected rows based on one or more attributes

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Commands Description

Comparison Operators

=,,, Used in conditional expression

Logical Operators

AND/OR/NOT Used in conditional expression

Special Operators

IS NULL Check whether an attribute value is null

LIKE Check whether an attribute value matches a given string patternDISTINCT Limit values to unique values

Aggregate Functions

COUNT Returns the number of rows with non-null values for a givencolumn

MIN Return the minimum attribute value found in a given columnMAX Return the maximum attribute value found in a given column

SUM Return the sum of all values for a given column

AVG Return the average of all values for a given column

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INSERT Command

Use INSERT command to enter data into a tableBasic syntax:

Note: Be careful with data type and allow-null attribute

INSERT INTO tablenameVALUES( value1, value2, , valueN)

INSERT INTO computers VALUES( '37', Lenovo Y550');

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INSERT Command (cont.)

Special case of INSERT1. Insert rows with null attributes

If we do not know some values of attribute, we have to leavethem as null

To enter a null, use following syntax

Note: You can insert NULL only the allow-null attribute

INSERT INTO tablenameVALUES(value1,NULL,,valueN)

INSERT INTO inventoryVALUES( '57', '2010-04-23', 37', 2', NULL);

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INSERT Command (cont.)

2. Insert rows with only required attributes Rather than declaring each attribute as NULL, indicate just

only the required value

To insert only some require attribute (e.g. col1, col2, ,

colN), use following syntax

INSERT INTO tablename(col1,col2,...,colN)VALUES(value1,value2,,valueN)

INSERT INTO inventory(inventoryID, dateAcquired, computerID, employeeID)

VALUES( '57', '2010-04-23', 37', 2');

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UPDATE Command

Use UPDATE command to modify data in a tableBasic syntax:

Note: Be careful about WHERE clause, there could be a hugeproblem if you forget to insert WHERE condition

UPDATE tablenameSET col1 = expression1,

col2 = expression2,

colN = expressionN[WHERE conditionList]

UPDATE inventorySET dateAcquired= 2010-08-22,comments = go go go

WHERE inventoryID = 57;

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DELETE Command

Use DELETE command to delete a table rowBasic syntax:

Note: Be careful about WHERE clause, there could be a hugeproblem if you forget to insert WHERE condition

DELETE FROMtablename[WHERE conditionList]

DELETE FROMinventory

WHERE inventoryID = 57;

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SELECT Command

Use SELECT command to query partial table contents by placingconditions we want specified in WHERE clause (optional)

Basic Syntax:

The columnList specifies the selected attribute we want, if we wantall attributes in that table, simply use *

SELECT columnList

FROMtablename[ WHERE conditionList ]

SELECT *FROM employee

SELECT employeeID, firstNameFROM employee

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SELECT Command (cont.)

Using a conditional expression in SELECT command

SELECT *FROM employees

WHERE lastName = 'Mouse'

SELECT *FROM employees

WHERE employeesID = 3

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SELECT Command Logical Operators

Use Logical Operatorsin SELECT command to connect multipleconditional expressions

AND / OR / NOT

SELECT *

FROM employeesWHERE lastName = 'Mouse'AND firstName = 'Mickey';

SELECT *FROM employees

WHERE (lastName = 'Mouse'ORlastName = 'Jetson')AND NOT(

firstName ='Mickey');

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SELECT Command Comparison Operators

Use Comparison Operatorsin SELECT command =,,,

SELECT *FROM employees

WHERE employeeID >10

SELECT *FROM employees

WHERE employeeID >10

AND lastName Jetson

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SELECT Command Special Operators: IS NULL

Use Special Operatorsin SELECT command1. IS NULL Operator

Use to check for a null attribute value

SELECT inventoryID, commentsFROM inventory

WHERE comments IS NULL

SELECT inventoryID, comments

FROM inventoryWHERE inventoryID >50AND comments IS NOT NULL

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SELECT Command Special Operators: LIKE

2. LIKE Operator Use with wildcards to find pattern within string attribute

% means any and all following character are eligibleP% include Paul, Peter, PatPa% include Paul, Pat, Parrot

_ means any one character may be substituted13_11 include 13A11, 13411_a_ include Rat, Van , Tap

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SELECT Command Special Operators: LIKE

2. LIKE Operator (cont)SELECT *FROM `computers`

WHERE computerDescriptionLIKE 'DELL%'

SELECT *FROM `employees`

WHERE lastName LIKE '_o_'

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SELECT Command Special Operators: DISTINCT

3. DISTINCT Operator Use DISTINCT operator to produce a list of unique attribute

values

SELECT DISTINCT computerIDFROM inventory

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SELECT Command Aggregate Function: COUNT

Use Aggregate Functionsto perform mathematical summary inSELECT command

1. COUNT Function

Use COUNT function to count the number of non-null values

of an attributeSELECT COUNT( * )FROM inventory

WHERE computerID =1

SELECT COUNT( comments )FROM inventory

WHERE 1

(there are totally 26 rows)

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SELECT Command Aggregate Function: MIN/ MAX

2. MIN/MAX Function Use MIN function to find the lowest value of a given attribute

Use MAX function to find the highest value of a givenattribute

SELECT MIN( computerID )FROM computers

SELECT MAX( computerID )FROM computers

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SELECT Command Aggregate Function: SUM

3. SUM Function Use SUM function to compute a total sum for any specific

attribute

SELECT SUM(computerID)FROM inventory

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SELECT Command GROUP BY

Use GROUP BY when you have other attribute columns combinedwith aggregate functions in SELECT command

Basic Syntax:

SELECT columnList

FROMtablename[ WHERE conditionList ][ GROUP BY columnList ]

SELECT employeeID,

COUNT( computerID )FROM `inventory`GROUP BY employeeID

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SELECT Command -- HAVING

Use HAVING clause when you want to specify condition ofGROUP BY clause in SELECT command

Basic Syntax:

SELECT columnListFROMtablename[ WHERE conditionList ][ GROUP BY columnList ][ HAVING conditionList ]

SELECT employeeID,

COUNT( computerID )FROM `inventory`GROUP BY employeeIDHAVING count(computerID)>1

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SELECT Command ORDER BY

Use ORDER BY in SELECT command to sort values in a givenattribute

Basic Syntax:

SELECT columnList

FROMtablename[ WHERE conditionList ][ GROUP BY columnList ][ HAVING conditionList ][ ORDER BY columnList [ASC | DESC]]

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SELECT Command ORDER BY

SELECT inventoryID,

employeeID,comments

FROM `inventory`WHERE inventoryID >40ORDER BY employeeID

SELECT inventoryID,

employeeID,comments

FROM `inventory`WHERE inventoryID >40ORDER BY employeeID DESC

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SELECT Command Joining Tables

Perform when data are retrieved from more than one tables

Normally compose of an equality comparison (=) of FK and PK ofrelated tables.

SELECT *FROMinventory, computers

WHERE inventoryID >40AND inventory.computerID = computers.computerID

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SELECT Command Join Tables : Alias

Use Aliasto identify the source table from which data are takenwhen join is performed

SELECT e.firstName, e.lastName,COUNT( * )AS 'number of computer'

FROM inventoryAS i, employeesAS eWHERE e.employeeID = i.employeeIDGROUP BY e.firstName, e.lastNameHAVING COUNT( computerID ) >1ORDER BY COUNT( * ) DESC