Granted, most of the work you will be doing
with web databases will probably be viewing. For that, the
SELECT-FROM-WHERE statements will be perfect for you. However,
in many cases you will also want browsers to be able to modify
your database. For example, perhaps you want them to be able
to add themselves to a mailing list.
The most basic database manipulation
is the INSERT operation that adds a new row to a
specified table. The INSERT operation follows the basic
syntax of:
INSERT INTO table_name (column_names)
VALUES (values);
For example, we might want to add a new
EMPLOYEE using:
INSERT INTO EMPLOYEES
(EMP_NUM, EMP_NAME, EMP_COMMISSION, EMP_SALARY)
VALUES
(004, 'Lee Eng Lock', '15%', 65000);
Of course, since we are assigning values for
each column, we need not specify the column names. thus, the following
statement would work as well:
INSERT INTO EMPLOYEES
VALUES
(004, 'Lee Eng Lock', '15%', 65000);
We now have:
EMPLOYEES Table |
EMP_NUM |
EMP_NAME |
EMP_COMMISSION |
EMP_SALARY |
001 |
Lim Li Chuen |
10% |
90000 |
002 |
Lim Sing Yuen |
20% |
40000 |
003 |
Loo Soon Keat |
20% |
50000 |
004 |
Lee Eng Lock |
15% |
65000 |
Note that when we perform an INSERT, the
incoming value must correspond to the data type defined for that
column. Thus, CHARACTER strings must be enclosed in single
quotes. Also note that if a row is inserted and some of the columns
are not defined, the column will be filled with NULL. Finally,
note that the order you specify columns and values does not matter, but if you
change the order, you must specify column names.
It is also useful to remember that there is no
concept of outside order to an SQL table. That is, you cannot know
which row will be stored first or last in a table. Thus,
you should be careful when assigning things such as unique
ordered row id numbers.
Finally, know that you can easily include a
SELECT-FROM-WHERE statement as the VALUE such as:
CREATE TABLE NEW_TABLE
(EMP_NAME CHAR (20),
CLIENT_NUM SMALLINT,
PRODUCT_NUM SMALLINT);
INSERT INTO NEW_TABLE
(EMP_NAME, CLIENT_NUM, PRODUCT_NUM)
SELECT EMPLOYEES.EMP_NAME,
SALES.C_NUM,
SALES.P_NUM
FROM EMPLOYEES, SALES
WHERE SALES.E_NUM = EMPLOYEES.EMP_NUM;
The resulting table would look like
NEW_TABLE Table |
EMP_NAME |
CLIENT_NUM |
PRODUCT_NUM |
Lim Li Chuen |
002 |
001 |
Lim Sing Yuen |
001 |
001 |
Lim Li Chuen |
003 |
002 |
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