Re: Student requests help with SQL

On 24-Apr-98 14:43:22 NChan50315 wrote:

>1. How does the query SELECT 'X' FROM SUPPLIERS; work where X is any
>character string and SUPPLIERS is the table name? When I look at the
>results I understand what the query is doing but why and how does it do
>it? I want to understand the inner functioning of the query

This query returns the constant 'X' for every row in the table SUPPLIERS. As far as I understand the thing, when you type

select <expr> from <table>;

the database evaluates the expression <expr> for every row of the table <table>. Well, if <expr> is constant... This also explains the existance of the DUAL table in Oracle. This one just has one single row containing 'x'. So when you type

select sysdate from dual;

you get the system date one time.

>2. When the timing SQL*PLUS system variable is turned on and a query
>executed, I get a (real:1210) in the output? What does (real:1210)
>mean? I understand that it has something to do with performance.

The number indicates the time elapsed while running your query in milliseconds.

>3. Do substitution variables (using &) in SQL*PLUS function similarly
>to the & address operator in C?

I don't think so. When typing something like

select * from your_table
where your_column = &a
or your_column = &a;

SQL*Plus actually queries two times for the value of a. So these variables have more similarity with text replacement macros of the C preprocessor.
The above example shows that SQL*Plus forgets the value of the variable immediately after using it which is not similar to any othar mechanism I know. It is just a quick way to request user input.

>4. I want to convert the online documentation on Forms to a hard copy.
> Is it possible to do it by a method other than copying and pasting
>into a word processor?

If your documentation is in HTML, you could make your browser print it. Everything else depends on how the documentation is available on your machine.

>5. How do I find out the version of Developer 2000 on my computer?

You could try starting Oracle Installer. It shows all installed Oracle products with their version number.
But I think Developer 2000 should display some version info at startup. I don't have a way to check that though.

>PLEASE email a copy of the answers to my address. Thank you very much.
>

No problem.

Hope that helps,
Lothar

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Lothar Armbrüster       | lothar.armbruester_at_rheingau.netsurf.de
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