sql query in java not working

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Hey I have this bit of code that is suppose to return true if the there is a student that already has this sutdentID and false in the other case. However the rowcount is always 0 and therefore the code always return false. The SQL statment seems to work, I've tested it on the database it self. Here is the code:

Java

String sql = ("SELECT * FROM std_details WHERE StudentID='"+id+"';");
		int rowCount = 0;
		ResultSet rs;
		try {
			rs = stmt.executeQuery(sql);
			while ( rs.next() )  
			{  
			    rowCount++;  
			}  
			System.out.println(rowCount);
		} catch (SQLException e1) {
			e1.printStackTrace();
		}

		if (rowCount > 0){
			return true;
		}else{
			return false;
		}

Posted 18-Dec-14 22:37pm

Member 11322545

Updated 18-Dec-14 22:38pm

v2

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Shweta N Mishra 19-Dec-14 5:22am

code seems to be correct, Did you have passed correct studentId in parameter ?

Member 11322545 19-Dec-14 5:37am

yea, I did I don't understand anymore :/

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Sinisa Hajnal · Accepted Answer · 2014-12-18T23:52:00

Solution 1

Change the code as follows:

C#

String sql = ("SELECT Count(*) as found FROM std_details WHERE StudentID='"+id+"';");
        int rowCount = 0;
        try {
rs = stmt.executeQuery(sql);
rs.next();  
rowCount = rs.getInt(1);
            System.out.println(rowCount);
        } catch (SQLException e1) {
            e1.printStackTrace();
        }
            return (rowCount > 0);
    }

Posted 18-Dec-14 23:52pm

Sinisa Hajnal

Updated 19-Dec-14 0:18am

v2

Comments

Member 11322545 19-Dec-14 6:06am

there is a compilation error on executeScalar, says i sould use execute instead, and I did think of using exists but i've been stuck on this function for a while so i decided to go the easy way. Finally I did not design the database, it does make sense indeed to have the id as an int.

Sinisa Hajnal 19-Dec-14 6:11am

Execute scalar: http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlcommand.executescalar%28v=vs.110%29.aspx

Which database are you using?

Member 11322545 19-Dec-14 6:12am

MySQL InnoDB and I'm using java

Sinisa Hajnal 19-Dec-14 6:18am

Solution updated for java...it should be database agnostic...it works because count(*) always returns a value.

Richard MacCutchan 19-Dec-14 6:29am

You should not use (or encourage others to use) string concatenation in SQL. Use proper parameterised queries.

Sinisa Hajnal 19-Dec-14 7:31am

I usually recommend stored procedures, rather then queries in code, but now I focused on the logic. :)

Richard MacCutchan 19-Dec-14 10:16am

I recognised that; it is just that we see so many examples of really bad usage that I tend to question it all the time.

Member 11322545 19-Dec-14 6:56am

This modified code still does not work I don't understand why ?
The query works in sql, so if I execute it straight on the database it works, but if I try to run it from Java the rowCount ends up being 0;

@ Richard, I totally agree but its out of my hands

Member 11322545 19-Dec-14 7:19am

fixed it, the problem was with ID, ID was not the actual ID, it was another number, sorry for disturbing.

Sinisa Hajnal 19-Dec-14 7:31am

Excellent. Feel free to accept the solution :)