mysql> ALTER TABLE vehicles ADD COLUMN (model_year

Int);[enter ]

Modifying Column Types

To change the data type of an existing field in a table with the

ALTER TABLE statement, use the following syntax:

ALTER TABLE table_name MODIFY [COLUMN] column_name

column_type;

Because the model_year field will hold only four-digit years, it can

fit in a two-byte SMALLINT rather than a four-byte INT. The following

statement changes the column type of the model_year field from INT

to SMALLINT in the vehicles table in the vehicle_fleet database:

mysql> ALTER TABLE vehicles MODIFY COLUMN model_year

SMALLINT;[ENTER ]

Unlike the ADD COLUMN clause, the MODIFY COLUMN clause applies to

only a single field.

Renaming Columns

To change the name of an existing field in a table with the

ALTER TABLE statement, use the following syntax:

ALTER TABLE table_name CHANGE [COLUMN] column_name

new_name column_type;

Be careful

407

The following statement changes the name of the miles field to

mileage in the vehicles table in the vehicle_fleet database:

mysql> ALTER TABLE vehicles CHANGE COLUMN miles mileage

FLOAT;[ENTER ]

Like the MODIFY COLUMN clause, the CHANGE COLUMN clause applies to

only a single field. The column_type must always be specified, even

if it doesn’t change. To change the data type of the field at the same

time, you specify the new column type for column_type. As when

using the MODIFY COLUMN clause, make sure that any existing data can

be converted to the new data type.

Renaming Tables

To change the name of an existing table with the ALTER TABLE

statement, use the following syntax:

ALTER TABLE table_name RENAME [TO] new_name;

The following statement changes the name of the vehicles table to

company_cars in the vehicle_fleet database:

mysql> ALTER TABLE vehicles RENAME TO company_cars;[ENTER ]

Removing Columns

To remove an existing field from a table with the ALTER TABLE state-

ment, use the following syntax:

ALTER TABLE table_name DROP [COLUMN] column_name;

The following statement removes the assigned_to column from the

company_cars table in the vehicle_fleet database:

mysql> ALTER TABLE company_cars DROP COLUMN assigned_to;[ENTER ]

You must be

Working with Databases and MySQL

Deleting Tables

To delete a table, you execute the DROP TABLE statement, which

removes all data and the table definition. The syntax for the

DROP TABLE statement is as follows:

DROP TABLE table;

408

Although the

The following statement deletes the company_cars table from the

vehicle_fleet database:

mysql> DROP TABLE company_cars;[ENTER ]

Short Quiz

1.

Explain the importance of selecting the most appropriate data

type for table fields.

Illustrate the SQL syntax to create a table.

What six columns are shown in the output of the

DESCRIBE table statement?

What SQL keywords are used with the ALTER TABLE statement

to add columns, modify columns, rename columns, or

remove columns for an existing table?

2.

3.

4.

Modifying User Privileges

MySQL assigns privileges to specify which actions and operations

a user can perform with a table or database. By default, only admin-

istrator accounts such as the root account have full permissions on

every database object. Regular users normally cannot create or drop

databases. Within a database, the database owner and the root user

are the only users who can create, alter, and drop tables, unless other

users are expressly granted these permissions. Users can also be

restricted in their ability to insert, update, delete, and select records

from tables.

For security purposes, user accounts should only be assigned the

minimum necessary privileges to perform given tasks. For example,

if a user should only be able to view records from a table, you should

only assign the SELECT privilege to the user’s account. This helps

secure your database by preventing the user from unintentionally (or

maliciously) changing or tampering with database records.

This section provides an overview of how to manage user privileges.

Table 7-4 lists common MySQL database privileges.

Privilege

ALL

ALTER

CREATE

DELETE

DROP

INDEX

INSERT

SELECT

UPDATE

USAGE

Description

Assigns all privileges to the user

Allows the user to modify the table structure

Allows the user to create databases, tables, and indexes

Allows the user to delete records

Allows the user to delete databases and tables

Allows the user to create and delete indexes

Allows the user to add records

Allows the user to select records

Allows the user to modify records

Creates a user with no privileges

Common MySQL database privileges

For informa-

409

Table 7-4

Granting Privileges

You use a GRANT statement to create user accounts and assign privi-

leges. The basic syntax for the GRANT statement is as follows:

GRANT privilege [(column)] [, privilege [(columns)] ...]

ON {table | * | *.* | database.*}

Privileges can be granted at the following levels: column, table, data-

base, and global. The first line in the GRANT statement syntax allows

you to specify individual columns to apply privileges. The ON por-

tion of the GRANT statement determines the level to which privileges

apply at the table, database, and global levels. You can specify the

name of an individual table in the current database or an asterisk,

which applies privileges to all the tables in the current database. If you

specify “*.*”, privileges are applied at a global level to all databases in

your MySQL installation. You can also indicate a specific table within

another database by appending the table name to the database name

with a period.

The GRANT statement creates the user account if it does not exist and

assigns the specified privileges. If the user account already exists, the

GRANT statement just updates the privileges. As an example, the fol-

lowing statement creates a new user named dongosselin and assigns

SELECT, INSERT, and UPDATE privileges to the user for all tables in the

currently selected database. The statement also assigns a password of

'rosebud' to the dongosselin account.

After you

Working with Databases and MySQL

mysql> GRANT SELECT, INSERT, UPDATE[ENTER ]

-> ON *[ENTER ]

The following statement assigns privileges to the user dongosselin to

a table named students in the currently selected database:

mysql> GRANT SELECT, INSERT, UPDATE[ENTER ]

-> ON students[ENTER ]

410

The following statement assigns privileges to the user dongosselin at

the global level to all databases in a MySQL installation:

mysql> GRANT SELECT, INSERT, UPDATE[ENTER ]

-> ON *.*[ENTER ]

The following statement assigns privileges to the user dongosselin to

the company_cars table in the vehicle_fleet database:

mysql> GRANT SELECT, INSERT, UPDATE[ENTER ]

-> ON vehicle_fleet.company_cars[ENTER ]

If you are

Finally, the following statement uses a wildcard (*) to assign privileges

to the user dongosselin to all tables in the vehicle_fleet database:

mysql> GRANT SELECT, INSERT, UPDATE[ENTER ]

-> ON vehicle_fleet.*[ENTER ]

All of the preceding examples specified the user dongosselin. MySQL

does not support wildcards for the user.

To create a new user account with privileges to the sitevisitors

database:

1.

2.

Return to MySQL Monitor.

Enter the following statement to create a new user account

with CREATE, DROP, ALTER, DELETE, INDEX, INSERT, SELECT, and

UPDATE privileges assigned to all the tables in the sitevisi-

tors database. The statement also assigns a password to the

account. Enter your own name (as one word) and a password

you will remember.

mysql> GRANT CREATE, DROP, ALTER, DELETE, INDEX,

INSERT, SELECT, UPDATE[ENTER ]

-> ON sitevisitors.*[ENTER ]

3.

Type exit or quit and press Enter to log out of MySQL.

4.

Enter the following command to log back in to MySQL with

the user account and password you just created:

mysql -u yourname –p

5.

When prompted, enter the new password you assigned to the

user account.

411

Revoking Privileges

You use the REVOKE statement to take away privileges from an exist-

ing user account for a specified table or database. The syntax for the

REVOKE statement is as follows:

REVOKE privilege [(column)] [, privilege [(columns)]] ...

ON {table | * | *.* | database.*}

The following example revokes INSERT and UPDATE privileges from

the dongosselin user account for the company_cars table in the

vehicle_fleet database:

mysql> REVOKE INSERT, UPDATE[ENTER ]

-> ON vehicle_fleet.company_cars[ENTER ]

The REVOKE ALL PRIVILEGES statement removes all privileges from a

user account for a specified table or database. The following example

takes away all privileges from the dongosselin user account for the

company_cars table in the vehicle_fleet database:

mysql> REVOKE ALL PRIVILEGES[ENTER ]

-> ON vehicle_fleet.company_cars[ENTER ]

You must be

In this chapter, the user account you created does not need the INDEX

privilege, so you revoke it in the next exercise.

To revoke privileges:

1.

2.

3.

4.

Return to MySQL Monitor.

Type exit or quit and press Enter to log out of MySQL.

Log back in to MySQL with the root account.

When prompted, enter the password you assigned to the root

account.

Enter the following command to revoke the INDEX privilege to

the tables in the sitevisitors database from your user account:

mysql> REVOKE INDEX[ENTER ]

-> ON sitevisitors.*[ENTER ]

5.

Working with Databases and MySQL

6.

7.

8.

Type exit or quit and press Enter to log out of MySQL.

Log back in to MySQL with your user account.

Enter the following command to select the sitevisitors

database:

mysql> use sitevisitors;[ENTER ]

412

Short Quiz

1.

2.

3.

Explain the term “user privileges.”

What are the four levels for which privileges may be granted?

What statement is used to take away privileges from an exist-

ing user account for a specified table in the database?

Working with Database Records

As described earlier, a record is a set of related field data stored as

a single row in a table. A table can store an unlimited number of

records, each with its own set of data. In this section, you will learn

how to add records to a table and how to update and delete existing

records.

Adding Records

You add individual records to a table with the INSERT statement. The

basic syntax for the INSERT statement is as follows:

INSERT INTO table_name (column1, column2, ...)

VALUES(value1, value2, ...);

The values you enter into the VALUES list will be stored, in order, in

the columns specified after the table name. Any values that you want

left NULL can be omitted from the column list, or you can put the

name in the column list and the keyword NULL in the corresponding

position in the VALUES list. For example, the following statement adds

a new row to the company_cars table in the vehicle_fleet database:

mysql> INSERT INTO company_cars (license, model_year,

make, model, mileage)[ENTER ]

-> VALUES('CK-2987', 2009, 'Toyota', 'Corolla',

You can also omit the column list, as follows:

INSERT INTO table_name VALUES(value1, value2, ...);

When you omit the column list, the values you enter in the VALUES list

must be in the same order in which you defined the table fields, and

each field in the table must have a specified value, even if the value

specified is NULL. For example, the following statement adds a new row

(record) to the company_cars table in the vehicle_fleet database:

mysql> INSERT INTO company_cars VALUES('CK-2987', 2009,[ENTER ]

-> 'Toyota', 'Corolla', 3508.4);[ENTER ]

413

Specify NULL in any fields for which you do not have a value. For

example, if you do not know the mileage of the vehicle, you can enter

NULL as the last item in the VALUES list, as follows:

mysql> INSERT INTO company_cars VALUES('CK-2987', 2009,[ENTER ]

-> 'Toyota', 'Corolla', NULL);[ENTER ]

Although it is permissible to omit the column list from the INSERT

statement, it is generally considered a poor programming practice. If

the structure of the table changes, values will not be assigned to the

appropriate columns.

To add two records to the pagevisits table in the sitevisitors

database:

1.

2.

Return to MySQL Monitor.

Enter the following command to add a record to the

pagevisits table:

mysql> INSERT INTO pagevisits (page_filename, visit_

date, visit_time,[ENTER ]

-> previous_page, request_method, remote_host,

3.

After you see the “Query OK” message, add another record, as

follows:

mysql> INSERT INTO pagevisits (page_filename, visit_

date, visit_time,[ENTER ]

-> previous_page, request_method, remote_host,

Your screen should look like Figure 7-10.

Working with Databases and MySQL

414

Figure 7-10

MySQL Monitor after adding two records to the pagevisits table

Sometimes you need to insert more than one row of data. You can

use multiple INSERT statements, but you also can insert multiple

records with a single INSERT statement, using the following syntax:

INSERT INTO table_name (column1, column2, ...)

VALUES(value1, value2, ...), (value1, value2, ...), ...;

In order to

As shown above, multiple VALUE lists are separated by commas. Each

value list is inserted as a separate record into the table. As with the

single-record INSERT statement shown previously, the column list is

optional, but should be included for good form.

For large data sets stored in external files, it is much more efficient to

use the LOAD DATA statement to add multiple records to a database

table. You use the LOAD DATA statement with the full path and name

of a local text file that contains the records you want to add. The syn-

tax for the LOAD DATA statement is as follows:

LOAD DATA INFILE 'file_path' INTO TABLE table_name

(column1, column2, ...);

Place each record in the text file on a separate line and place tabs

between each field. The fields will be stored into the columns speci-

fied in the column list in the order specified. As with the INSERT

statement, the column list is optional, but should always be used.

If the column list is omitted, the values on each line must be in the

same order in which you defined the table fields. For missing field val-

ues, do not use the keyword NULL, because it will be interpreted as the

text value “NULL”, not as a NULL value. Simply use consecutive tabs

with nothing between them.

The following statement loads a file named company_cars.txt into the

company_cars table in the vehicle_fleet database:

mysql> LOAD DATA INFILE 'company_cars.txt' INTO TABLE

company_cars;[ENTER ]

To add new records to the pagevisits table in the sitevisitors

database:

1.

2.

The optional

If your MySQL

Use the

MySQL serv-

er’s direc-

tory path,

not the Web

URL path.

The path

415

Return to MySQL Monitor.

Enter a LOAD DATA statement that inserts records from the

page_visits.txt file in your Chapter directory for Chap-

ter 7. Be certain to enter the full path for the location of

your data files. Enter the following command, replac-

ing path_to_PHP_folders with the full path for your

PHP_Projects directory:

mysql> LOAD DATA INFILE 'path_to_PHP_folders/

Chapter.07/Chapter/page_visits.txt'[ENTER ]

-> INTO TABLE pagevisits [ENTER ]

3.

You should see a result similar to the following:

Query OK, 12 rows affected (0.01 sec)

Records: 12 Deleted: 0 Skipped: 0 Warnings: 0

mysql>

Retrieving Records

You use the SELECT statement to retrieve records from a table. The

basic syntax for a SELECT statement is as follows:

SELECT criteria FROM table_name;

You use the asterisk (*) wildcard with the SELECT statement to

retrieve all fields from a table. You can also specify individual fields to

return by separating field names with a comma. The following state-

ment returns the model and mileage fields from the company_cars

table in the vehicle_fleet database:

Working with Databases and MySQL

mysql> SELECT model, mileage FROM company_cars;[ENTER ]

+---------+---------+

| model| mileage |

+---------+---------+

| Corolla | 3508.4 |

| Cobalt | 24829.4 |

| Focus| 24829.4 |

| Civic| 48891.1 |

| Sentra | 28336.7 |

| Accord | 77484.4 |

| Camry|855.5 |

| Fusion |95.9 |

| Malibu | 57024.2 |

| Sonata | 62993.6 |

| Altima | 17398.3 |

+---------+---------+

11 rows in set (0.00 sec)

416

To enter SELECT statements that return records from the pagevisits

table in the sitevisitors database:

1.

2.

Return to MySQL Monitor.

Enter the following SELECT statement, which returns all

records from the pagevisits table. Your output should look

like Figure 7-11, although the lines might wrap, depending on

your screen resolution.

mysql> SELECT * FROM pagevisits;[ENTER ]

417

Figure 7-11

3.

SELECT statement that returns all records from the pagevisits table

Enter the following SELECT statement, which returns the

visit_date, previous_page, and page_filename fields

from the pagevisits table. Your output should look like

Figure 7-12.

mysql> SELECT visit_date, previous_page, page_

filename FROM pagevisits;[ENTER ]

Working with Databases and MySQL

418

Figure 7-12

SELECT statement that returns the visit_date, previous_page, and

page_filename fields from the pagevisits table

Using Aggregate Functions

You often need to summarize data in a set of records, rather than

view the individual records. SQL offers various functions that you

can include in queries to retrieve this aggregate data. Table 7-5 shows

these functions.

Function

AVG()

COUNT()

GROUP_CONCAT()

MAX()

MIN()

STD()

STDDEV_POP()

STDDEV_SAMP()

STDDEV()

SUM()

VAR_POP()

VAR_SAMP()

VARIANCE()

Description

Return the average value of the argument

Return a count of the number of rows returned

Return a concatenated string

Return the maximum value

Return the minimum value

Return the population standard deviation

Return the population standard deviation

Return the sample standard deviation

Return the population standard deviation

Return the sum

Return the population standard variance

Return the sample variance

Return the population standard variance

SQL aggregate functions

Table 7-5

The GROUP_CONCAT() and VARIANCE() functions were added

in Version 4.1 of MySQL. The STDDEV_POP(), STDDEV_SAMP(),

VAR_POP(), and VAR_SAMP() functions were added in Version 5.0.3

of MySQL.

The COUNT() function has two unique features when compared to

the other aggregate functions. First, you can use the wildcard (*)

instead of a field name as the function argument. Second, the key-

word DISTINCT can be used after the opening parenthesis. When the

DISTINCT keyword is used, each unique value is counted as 1, no mat-

ter how many records contain that value.

There are two ways to use the aggregate functions. If only aggregate

functions are used in the SELECT statement, the aggregate values

include all records returned based on the WHERE clause. The following

query will return 31476.991042397, the average of the mileage col-

umn for all records in the company_cars table:

mysql> SELECT AVG(mileage) FROM company_cars;[ENTER ]

419

To retrieve aggregate values for groups of records, you use the

GROUP BY clause and include the fields that you use to group the

records as part of the query. The following query will return the aver-

age mileage for each model year:

mysql> SELECT model_year, AVG(mileage)[ENTER ]

-> FROM company_cars[ENTER ]

To determine the number of pages visited from each remote_host:

1.

2.

Return to MySQL Monitor.

Enter the following SELECT statement, which returns each

remote_host from the pagevisits table with the number of

pages visited from that remote_host. Your output should look

like Figure 7-13.

mysql> SELECT remote_host, COUNT(*)[ENTER ]

-> FROM pagevisits[ENTER ]

Working with Databases and MySQL

420

Figure 7-13

SELECT statement that returns the total number of visits from each

remote_host in the pagevisits table

3.

Enter the following SELECT statement, which returns each

remote_host from the pagevisits table with the number of

distinct pages visited from that remote_host. Note that the

wildcard was replaced by the name of the field that contains

the names of the pages visited. Your output should look like

Figure 7-14. Because three of the remote_host values had

multiple records with the same value in the page_filename

field, those three values had fewer distinct records than they

had records.

mysql> SELECT remote_host, COUNT(DISTINCT page_

filename)[ENTER ]

-> FROM pagevisits[ENTER ]

Figure 7-14 SELECT statement that returns the number of different pages visited from

each remote_host in the pagevisits table

Sorting Query Results

You use the ORDER BY keyword with the SELECT statement to per-

form an alphanumeric sort of the results returned from a query.

The following statement returns the make and model fields from the

company_cars table in the vehicle_fleet database and sorts the

results by the make field. The statement also performs a secondary

sort on the model field:

mysql> SELECT make, model FROM company_cars ORDER BY make,

model;[ENTER ]

+-----------+---------+

| make| model|

+-----------+---------+

| Chevrolet | Cobalt |

| Chevrolet | Malibu |

| Ford| Focus|

| Ford| Fusion |

| Honda| Accord |

| Honda| Civic|

| Hyundai| Sonata |

| Nissan| Altima |

| Nissan| Sentra |

| Toyota| Camry|

| Toyota| Corolla |

+-----------+---------+

11 rows in set (0.01 sec)

421

To perform a reverse sort, add the DESC keyword after the name of

the field by which you want to perform the sort. (DESC stands for

“descending.”) The following statement returns the

mysql> SELECT make, model FROM company_cars ORDER BY make

DESC, model;[ENTER ]

+-----------+---------+

| make| model|

+-----------+---------+

| Toyota| Camry|

| Toyota| Corolla |

| Nissan| Altima |

| Nissan| Sentra |

| Hyundai| Sonata |

| Honda| Accord |

| Honda| Civic|

| Ford| Focus|

| Ford| Fusion |

| Chevrolet | Cobalt |

| Chevrolet | Malibu |

+-----------+---------+

11 rows in set (0.00 sec)

Working with Databases and MySQL

To enter several SELECT statements that sort records from the

pagevisits table in the sitevisitors database:

1.

2.

422

Return to MySQL Monitor.

Enter the following SELECT statement, which returns the

visit_date, previous_page, and page_filename fields from

the pagevisits table, and sorts the returned records by

previous_page and page_filename. Your output should look

like Figure 7-15.

mysql> SELECT visit_date, previous_page, page_

filename[ENTER ]

-> FROM pagevisits ORDER BY previous_page, page_

Figure 7-15

SELECT statement that returns the visit_date, previous_page, and

page_filename fields from the pagevisits table, and sorts the returned records by

previous_page and page_filename

3.

Enter the following SELECT statement, which returns the

visit_date, previous_page, and page_filename fields from

the pagevisits table, and performs a descending sort of the

returned records by visit_date. Your output should look like

Figure 7-16.

mysql> SELECT visit_date, previous_page, page_

filename[ENTER ]

-> FROM pagevisits ORDER BY visit_date

423

Figure 7-16

SELECT statement that returns the visit_date, previous_page, and

page_filename fields from the pagevisits table, and performs a descending sort of the

returned records by visit_date

Filtering Query Results

The criteria portion of the SELECT statement determines which

fields to retrieve from a table. You can also specify which records

to return by using the WHERE keyword. For example, the following

statement returns all records from the company_cars table in the

vehicle_fleet database in which the make field is equal to “Toyota”:

mysql> SELECT * FROM company_cars WHERE make='Toyota';[ENTER ]

+---------+--------+---------+---------+------------+

| license | make| model| mileage | model_year |

+---------+--------+---------+---------+------------+

| CK-2987 | Toyota | Corolla | 3508.4 |2009 |

| 8331-RT | Toyota | Camry|855.5 |2010 |

+---------+--------+---------+---------+------------+

2 rows in set (0.00 sec)

SQL includes the keywords AND and OR that you can use to specify

more detailed conditions about the records you want to return.

For example, the following statement returns all records from the

company_cars table in the vehicle_fleet database in which the

model_year field is equal to 2007 and the mileage is less than 60000:

Working with Databases and MySQL

mysql> SELECT * FROM company_cars WHERE model_

year=2007[ENTER ]

-> AND mileage<60000;[ENTER ]

424

The following statement shows an example of how to use the OR key-

word by returning all records from the company_cars table in the

vehicle_fleet database in which the make field is equal to “Toyota”

or “Honda”. The statement also sorts the returned records by mileage.

mysql> SELECT * FROM company_cars WHERE

make='Toyota'[ENTER ]

-> OR make='Honda' ORDER BY mileage;[ENTER ]

To enter several SELECT statements that use the WHERE keyword to fil-

ter records from the pagevisits table in the sitevisitors database:

1.

2.

Return to MySQL Monitor.

Enter the following SELECT statement, which returns

all records from the pagevisits table in which the

previous_page field is equal to “index.php”. Your output

should look like Figure 7-17.

mysql> SELECT * FROM pagevisits WHERE

previous_page='index.php';[ENTER ]

425

Figure 7-17 SELECT statement that returns all records from the pagevisits table

in which the previous_page field is equal to “index.php”

3.

Enter the following SELECT statement, which returns all

records from the pagevisits table in which the remote_port

field is greater than 80. Your output should look like

Figure 7-18.

mysql> SELECT * FROM pagevisits WHERE remote_

port>80;[ENTER ]

Figure 7-18 SELECT statement that returns all records from the pagevisits table

in which the remote_port field is greater than 80

Updating Records

If you need to update records in a table, you use the UPDATE state-

ment. The basic syntax for the UPDATE statement is as follows:

UPDATE table_name

SET column_name=value

WHERE condition;

Working with Databases and MySQL

The UPDATE keyword specifies the name of the table to update, and the

SET keyword specifies the value to assign to the fields in the records

that match the condition in the WHERE keyword. For example, the fol-

lowing statement modifies the mileage of the Ford Fusion to 368.2:

426

mysql> UPDATE company_cars SET mileage=368.2[ENTER ]

-> WHERE make='Ford'[ENTER ]

Notice that the preceding statement uses the WHERE keyword to spec-

ify that the make field should be equal to “Ford” and the model field

should be equal to “Fusion”. This ensures that only the correct record

is updated. If the statement only specified that the make field should

be equal to “Ford”, the mileage field would have been updated to

368.2 for all other records in the table that included a make field with

a value of “Ford”.

Next, you enter several UPDATE statements to modify records from

the pagevisits table in the sitevisitors database. The table

contains one record that includes a value of “contact.php” in the

previous_page field and another record that includes “contact.php”

in the page_filename field. Assume that the page name has been

changed to “contact_us.php.”

To enter several UPDATE statements to modify records from the

pagevisits table in the sitevisitors database:

1.

2.

Return to MySQL Monitor.

Enter the following UPDATE statement to modify the

previous_page field in records in the pagevisits table from

“contact.php” to “contact_us.php” (two rows will be changed):

mysql> UPDATE pagevisits[ENTER ]

-> SET previous_page='contact_us.php'[ENTER ]

3.

Enter the following UPDATE statement to modify the

page_filename field in records in the pagevisits table

from “contact.php” to “contact_us.php” (three rows will be

changed):

mysql> UPDATE pagevisits[ENTER ]

-> SET page_filename='contact_us.php'[ENTER ]

4.

Enter the following SELECT statement to view all the records

in the table. The "contact.php" values should now be

"contact_us.php."

mysql> SELECT * FROM pagevisits;[ENTER ]

Deleting Records

To delete records from a table, you use the DELETE statement. The

basic syntax for the DELETE statement is as follows:

DELETE FROM table_name

WHERE condition;

427

Be careful when you use the DELETE statement because it deletes all

records that match the condition. Therefore, carefully construct the

conditions assigned to the WHERE keyword. For example, the follow-

ing statement deletes the record for the 2006 Honda Accord from the

company_cars table in the vehicle_fleet database:

mysql> DELETE FROM company_cars WHERE model_

year=2006[ENTER ]

-> AND make='Honda'[ENTER ]

A bug in some

To delete all the records from a table, omit the WHERE clause. The fol-

lowing statement deletes all the records from the company_cars table:

mysql> DELETE FROM company_cars;[ENTER ]

Query OK, 10 rows affected (0.28 sec)

To delete several records from the pagevisits table in the

sitevisitors database:

1.

2.

Return to MySQL Monitor.

Enter the following statement to delete the first record in the

table:

mysql> DELETE FROM pagevisits WHERE

visit_date='2012-03-17'[ENTER ]

-> AND visit_time='10:32:29';[ENTER ]

3.

Enter the following statement to delete the next record in the

table:

mysql> DELETE FROM pagevisits WHERE

visit_date='2012-03-17'[ENTER ]

-> AND visit_time='10:35:18';[ENTER ]

4.

Enter the following SELECT statement to view all the records

in the table. The table should now only consist of 12 records.

mysql> SELECT * FROM pagevisits;[ENTER ]

Short Quiz

1.

When the column names are omitted from the INSERT INTO

statement, what two important considerations must be

followed?

Working with Databases and MySQL

2.

What SQL command is used to add records from an external

text file?

What value should be entered in a text field as a placeholder

for missing values?

What clause can specify the delimiter in a text file that is used

as a data source for a MySQL table?

What keyword is used to specify a reverse or descending sort

order for selected records in a table?

3.

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4.

5.

Working with phpMyAdmin

You must learn the proper SQL syntax to store, manipulate, and

retrieve data in a MySQL database from PHP, but SQL can be cum-

bersome for database administration and maintenance. Normally, you

create the table structure in MySQL using a graphical interface and

maintain the data with PHP.

Be sure that

The phpMyAdmin application is an open source tool written in PHP

to handle the administration of MySQL databases. The phpMyAdmin

tool can perform all of the administrative tasks that you’ve already

studied in this chapter, plus many others you haven’t learned yet. The

full functionality of phpMyAdmin is beyond the scope of this section,

but you will learn the basics of the interface and be exposed to some

common activities.

Logging in to phpMyAdmin

Your instructor should have provided you with a link to a Web page

for logging in to phpMyAdmin. When you visit the Web page, you

should see a page like the one shown in Figure 7-19. Enter the user

name and password provided by your instructor in the appropriate

fields, and then click the Login button.

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Figure 7-19

The phpMyAdmin login page

Different ver-

If you enter an incorrect user name or password, you will see a page

like the one shown in Figure 7-20, with an error message above the

Login button. The error message will be something like “#1045 -

Access denied for user ‘username’@‘ host’ (using password: YES)”,

where username is the user name that you entered, and host is the

name of the computer you are using. The user name and password

fields are still available, so you can attempt to log in again.

Working with Databases and MySQL

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Figure 7-20

The phpMyAdmin invalid login message

Once you have successfully entered your user name and pass-

word, you should see the phpMyAdmin main screen, as shown in

Figure 7-21. Whenever you need to return to the main screen, click

the small house icon in the upper-left corner.

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Figure 7-21

The phpMyAdmin main screen

If you have access to more than one database, the left side of the

screen will display a drop-down list of databases to which you have

access, with the number of tables in each database listed in parenthe-

ses after the name. When you select the database, the phpMyAdmin

main screen appears. The name of the selected database and its tables

will be listed on the left side of the screen below the drop-down list.

Figure 7-21 shows a database (student200) with no tables defined.

Working with Databases

If you do not have access to more than one database, and you do not

have privileges to create databases, you can skip this section.

The right side of the main screen has two columns, one for MySQL

and one for phpMyAdmin. The first option under the MySQL col-

umn header is “Create new database”. If you do not have privileges

to create a new database, you cannot select this option, and the mes-

sage “No Privileges” will appear beneath it, as shown in Figure 7-21.

If you have privileges, a text box appears beneath the “Create new

database” option with a Create button beside it. Enter the name of

the new database and click the Create button. The database will be

created and selected as the active database, much like entering the

USE database command in MySQL Monitor.