Using comments in a query

[Vishravars Ramasubramanian]

I found a peculiar problem when i tried retrieving values from a table using JDBC.

I had 2 parts of a queries separated by UNION. When i used the m$ sql comment "--" in the first part of the query, the code after union did not get executed. Say for example:-

sbSample.append("select 'abcd', 'efgh'");
sbSample.append("--order by 1");
union
sbSample.append("select 'ijkl', 'mnop'");

(sbSample is a StringBuffer type)
then executing the query using create statement to follow.

the result was
abcd
efgh (assume that i printed the result in some loop)

I have not tried any other combination yet.

Explanation/tips on how to observe this more detailed are highly welcome.

[Paul Sturrock]

So you are saying that SQL that has been commented out does not run?

This is no surprise, is it? Assuming sbSample is a StringBuffer what you've coded will produce one line of SQL.

[Jan Cumps]

It doesn't work. Everything in your statement ends up in one long string.
So everything after the -- would be seen as comment:

Also, union is not a valid java command. Your code will not compile.

select x from y -- order by x union select y from z

Using -- as comments might also make your code incompatible with other databases.
It might be better to put the comments in your javacode:

sbSample.append("select 'abcd', 'efgh' from x ");
<a href="http:////" target="_blank" rel="nofollow">//</a> sbSample.append("order by 1");
[B]sbSample.append("[/B]union [B]" );[/B]
sbSample.append("select 'ijkl', 'mnop' from y");

Regards, Jan

[Vishravars Ramasubramanian]

eek that was a typo. union is part of the string .

and yes putting // comments will work fine and -- wont make sense in other db's.

Point needed is why the result is that way.

[Raghavan Muthu]

Originally posted by vishravars vishravars:

Point needed is why the result is that way.

That's because as Jan Cumps said the "--" causes the whole remaining portion of SQL to be commented.

Just do a System.out.println of your StringBuffer and take the output as it is and run it in the SQL editor. You will get to know.

[Vishravars Ramasubramanian]

Thank you all. I am clear now. Later used profiler to find the commented part of the query. I felt hard to locate the bug because that one line comment was hidden in the dark. So got confused with the way the comments work.

Thanks all once again.

[Jesper de Jong]

"vishravars",

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