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Okay, enough of all that DB Admin stuff.
Let's get down to the nitty gritty of retrieving data from your
database.
In SQL, the "SELECT - FROM" statement
is used to grab data from a database. The statement follows
the generic syntax of:
SELECT column_name
FROM table_name;
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There are a few things to notice about
the format of this SQL statement that will help us understand
all SQL statement formats.
First, notice that the statement
ends in semicolon. Like English, SQL requires termination
punctuation so that the SQL database will know when you
are done speaking to it. In the case of SQL, the semicolon (;)
character works like the period in English.
Second, notice that
the statement spans multiple lines. This is more of
a convention than a necessity. Like HTML, SQL ignores
whitespace in a statement, so you could just as easily write
SELECT column_name FROM table_name. The reason we break the
statement up into multiple lines is to increase readability. As
your SQL statements get more and more complex, you will find
that if you break them up into logical blocks, they will be
easier to read.
Finally, notice that we have used all
uppercase letters for our keywords (like SELECT and FROM).
This is a good idea as even though most implementations of
SQL are case insensitive, some are. Okay, let's get back
to the example...
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In other words, if you wanted to get
all the names of the employees in the EMPLOYEE table, you
would type:
SELECT EMP_NAME
FROM EMPLOYEES;
In the case of our
sample database, you would get
the following results:
EMP_NAME
-------------
Lim Li Chuen
Lim Sing Yuen
Loo Soon Keat
-------------
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We are going to be using the
sample database throughout the
day in order to show examples, so get familiar with the
tables.
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You needn't limit yourself to single
columns of course, The column_name parameter may take
a comma delimited list so that if you also wanted a report for
the employee number and salary, for example, you would simply
use:
SELECT EMP_NAME, EMP_NUMBER, EMP_SALARY
FROM EMPLOYEES;
In this case, you would get the following
results:
EMP_NAME EMP_NUMBER EMP_SALARY
------------------------------------------
Lim Li Chuen 001 90,000
Lim Sing Yuen 002 40,000
Loo Soon Keat 003 50,000
------------------------------------------
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Note that if you specify a
column name that does not exist, you will get an error.
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