MAX(ROWID) and inserting rows at the end of the table

Question

Hi,
I know this will be another lame question but I simply didn't find the answer anywhere. I create ID (primary key) for rows manually so I have this code:
String query = "SELECT * FROM CIS_SEG_SKUPINY WHERE ROWID=(SELECT MAX(ROWID) FROM CIS_SEG_SKUPINY)";
rset = stmt.executeQuery(query);
if (!rset.next()) {
<p style="padding-left:10px">newID = new Number(1);
System.out.println(newID);</p>
else {
<p style="padding-left:10px">rset.beforeFirst();
while (rset.next()) {
<p style="padding-left:20px">int lastID = rset.getInt("ID");
System.out.println(lastID);
newID = new Number(lastID + 1);
System.out.println(newID);
}</p>
}</p>
css.setId(newID);
Row globalsRow = getGlobals().first();
css.setKodSegSkupiny((String)globalsRow.getAttribute("GroupCode"));
css.setPopis((String)globalsRow.getAttribute("Description"));
css.setBarva((Number)globalsRow.getAttribute("Colour"));
getDBTransaction().commit();
When the table is empty newID is set to 1 and row inserted. Now I have one row in the table (with ID=1) so newID is set to 2 and row inserted BUT it is inserted BEFORE the first row. So when I try to insert third row lastID is 1 not 2. I tried to find some command which would insert new row after the last one but unfortunately I wasn't successfull.
Edited by: Herald on Mar 28, 2009 11:11 AM

Answer 1

Herald,
I am sorry to say that there are so many things wrong with your approach, that I don't know where to begin...
1). ROWID is a pseudo column in Oracle.. It has no meaning of first, last, middle, or otherwise. SELECT MAX(ROWID) will get you some row.
2). In a relational database, there is no concept of first or last row in a table. If you expect the rows in some order, use an order by.
3). Ignoring your implementation and addressing your intent - you should not be creating a primary key by getting the max already in the table and adding one. You will, using your technique, get duplicates in a multi-user scenario. If you fix your implementation to not give duplicates in a multi-user scenario (no, I won't show you how), you will use a table lock, and therefor inhibit scalability in a serious way.
The proper and commonly accepted way to generate a numeric primary key in Oracle would be to use a sequence and a trigger to populate the sequence. Lots of examples to be found in this forum, but just have a read of the ADF Developers Guide for Forms/4GL Developers (for 10g) or the Fusion Developers Guide (for 11g) to find one. The term to search for would be DBSequence.
John