visual foxpro ch2 by chang yu1 chapter two database management part one database definition record...

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Chapter TwoDatabase Management

Part one• Database definition

• Record and Field

• Type of columns

• Expression

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2.1 Database and Table

• Database : An organized collection of logically related tables. (staff.dbc )

• Table: An organized collection of related data. ( student.dbf, course.dbf)

• A record consists of one or more columns.

• A table consists of one or more records.

• A database consists of one or more tables.

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record

columntable

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2.2 Expression

• ? < Expression> ---- this command will display the result of the expression on the main screen.

? 32+5 , ? pay , ? sqrt(100)

• Go < nRecordNumber> ---- this command will move the pointer to the nth record of the table.

Use d:/basic/person.dbf

Browse

go 3

? pay

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2.2 Expression

• Five kinds of expression:• Numeric Expression 34 + 34

• Character Expression “ ABC” + “DEF”

• Date Expression Date( ) +20

• Logical Expression Not .T.

• Relation Expression 34 > 12

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2.2 Expression

< operand 1> < operator> < operand 2 > 32 + 56 • The operand 1 and operand 2 must match the data type.• The operator may be an unary operator.

• Not • “ -” -32 , not .t.

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2.2 Expression

• The types of operants :• Constant

• Variable » use only with letters and “_” and numbers .

» 128 letters.

» begin with letters or “_”.

» Can not use with keywords.

• Column name

pay, xname…

• Function Date(), LEFT( “abcdefg” , 3”)

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2.2 Expression

• The kinds of expression :

• Numeric expression: + , - ,^ , ** , * , / , %

• Character expression: + , -

• Date expression: +, -

• Logical expression: NOT, AND, OR

• Relation expression: =, #, < >, > , < ,>= , <= , $

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Operator Example Result

+ - 3 + 4 7

^ ** 3 ^ 4 81

* / 30 / 6 5

% 10 % 3 1

Numeric Expression:

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Operator Example Result

+ “ABC ”+ “DEF” “ABC DEF”

- “ABC ” – “DEF” “ABCDEF ”

Character Expression

Operator Example Result

+ {^1999.05.11} + 50 {^1999.06.30}

- {^1999.05.11} - 50 {^1999.03.22}

- {^1999.05.11} - {^1999.03.22} 50

Date Expression

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.T..T. OR .F.OR

.T..T. AND .T.AND

.F.NOT .T.NOT

ResultExampleOperator

Logical Expression

.T.“ABCD” = “AB”=

.T.“AB” $ “ABCD”$

.F.32 # 32#, < >

ResultExampleOperator

Relation Expression

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? 66 + sqrt(4)? 66 + pay? 3 ^ 4? 23 % 7? 1/3set decimals to 4? 1/3? “ABC” + Left(“defgh”, 3)?date() + 19? {^1999.06.03} -100? 3 # 4? “caa”> “bbb”

Exercise

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? {^1999.06.03}-{^1999.02.23}

? 100 + date( )

? {^1999.06.03} + {^1999.02.23}

? A = .F.

? .T. ANF .F.

? .T. AND A

? NOT .T.

? NOT .T. OR .F. AND .T.

? “a” > “b”

? “caa” > “bbb”

? “abcd” = “ab”

set exact on

? “abcd” = “ab”

EXERCISE

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Database managementPart two

• Database• Create database• Select database• modify database• Close database

• Table– Free table– Database table

– Create table– Open table and close table– Modify table– Select work Area

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The type of the column • Character : 1--254 letters(127 Chinese words) , for any word.

• Currency : For money.• Numeric : For numeric value.

• Float : For numeric value.• Date Time : 0001.0101 --9999.132.31. For date and time.

• Double : Double precise float number. Width 8• Integer : -214783647--2147483646. Width 4.• Logic : true or false.• Memo : 4 bytes. (*.fpt). Unlimited width.• General : music, picture, video. 4 bytes.

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2.3 Create Database

• Database table :

– A table which is in the database.

create database staff

create

• Free table :

– A table which is independent and is not in any

databases.

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2.3.1 Create new database

• Use the menu bar– file --> new --> database --> database name.

• Command: Create database [<dbname> | ? ]• this command will create a new database.

• Command: Modify database [ <dbname> ]• this command will call the database designer to modify and

display the database structure.

• Project manager

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2.3.2 Create new table

• Use the menu bar : – > file -> open -> table -> input table name

• Command: Create [ <table name> | ? ]

• Press the right button of mouse in the database designer :– database designer -> press the right button of the mouse -> choice

the new table -> input the table name “persoin1.dbf”

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2.3.3 Design the table structure

• Name : column name , 128 letters.

• Type : the type of a column.

• Width : the width of a column.

• Floating point number : the number of

decimal points.

• Caption: input the Chinese column name.

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2.3.3 Design the table structure

• Field Validation : • Rule : .NOT. EMPTY (NO)• Message: the staff-no must be entered in the table.• Append : insert the data to test the rule and message.

• Default value:• Field command:• Entry the data: Ctr-w to save the data. (Esc)• Table name:• Field Validation of a table:

– rule and message. – .NOT.(empty(addr).AND.empty(tel))

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2.3.4 Create a free table

• A free table is independent. It is not in any databases. So we do not need to open any database before we create a free table.– Use the menu bar– Command: Create < tablename>

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2.4 How to use databases-- open a database

• Open a database:– use the menu bar– Command:

OPEN DATABASE [<databasename> | ? ] [ Exclusive | Shared]

• Exclusive : A keyword indicates that the database cannot be opened by more than one user at a same time.

• Shared : the database can be opened by more than one user at a same time.

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Convert a database

• Visual FoxPro allows a user to open more

than one database at any time, but he/she

can manipulate only one database at a time.

• Use the tool bar. Using the mouse to choice.

• Command: SET DATABASE TO[<databasename>]

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Close a database

• Close Database – this command will close the database which is

being used now.

• Close All– this command will close all databases which be

opened by the user.

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Modify a database

• Modify Database [ < DatabaseName > | ? ] – Modify Database library = Open database library + modify database

• View and modify a table :

• Based on the database designer, a user can use the

right button of the mouse on the table structure to

view, delete and modify a table.

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Modify a database

• Add a free table in a database:– The table must be free table.

– The table must be closed.

– Cannot add any database table.

• Move the table from a database:– The database must be opened in the exclusive mode.

– The table must be closed.

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Open a table -- USE

• Visual FoxPro allows a user to open more than one table. But you can choice only one table to manipulate at a time.

• Work Area is a place where a table can be opened. There are 225 Work Areas. One table can be opened on only one workArea. So we can open up to 225 tables at a time.

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WorkArea

1

2

3

224

225

database

table

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USE

• Any time we can modify and edit only one database and one table, although we can open many databases and many tables.

• Open table:– use menu bar: file -> open -> *.dbf -> person.dbf

– command: Use [ < tablename> | ? ]

– [use <tablename>] can open the table in workArea one. If we open more tables, we should select other workAreas.

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Select a WorkArea• Select < nWorkArea > |< cTableAlias >

– close all– open database library– use book ALIAS book-data– select 2– use student ALIAS student-data– ...– select book-data ( = select 1 )– select student-data ( = select 2 )

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Select a WorkArea

• Use [ < tablename | ?] [Alias <aliasname>] [Exclusive | Shared ] [In <nworkarea> |<ctablealias>]

• – close all– open database library– use student in 5 – use book in 0– use course in A Minimum workarea number

select 5

use student

= use course in 1

*Workarea A—j represent workarea 1—10 respectively.

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Modify table Structure

• Use database designer– press the right button of mouse on the table.

• Command: Modify Structure– open database staff1– use person1– modify structure

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ExerciseDesign the database score.dbc and two tables: Score1.dbf

Column-name TYPE WIDTH Description

stuid character 9 Student no

Cour_num character 5 Course no

Score1 numeric 5.1 midterm

Score2 numeric 5.1 Final_exam

Flag character 1

Req_sel character 1 Major/Minor

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Exercise

Column-name Type Width Description

Cour_num character 5 course no

grade character 1 term no

credit numeric 3.1 grade

hour numeric 1 hour

Chin_name character 30 Course name

Eng_name character 60 Course name

Course1.dbf

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Command? <Expression>

Go <nRecordNumber>

Create database [ <dbname> | ? ]

Create [ <tablename> | ? ]

Open database [ <databasename> | ? ]

Set database to [ < dbname> ]

Close database

Close all

Modify database [ <dbname> | ? ]

Use [ <tablename> | ? ] [ Alias <aliasname> ]

Select <nworkarea> | <ctableAlias>

Use <tablename> IN <nworkarea> | <ctableAlias>

Create

Create table-name

Create ?

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Question:1. Open database library

Use student use student

Use loan use loan in 0

Use book use book in 0

2. Select 5

Use person ALIAS ppp

3. Select A

use person

select C

use course

?

Result ?

= use person in 1

= use course in 3

?