Learn, Share, Build

--- EDITED with correct comment from Shaido ---

Usually, GROUP BY would handle this, if the order in the table is irrelevent,

SQL is good with grouping large amount of related data. However, your analysis is dependent on the order of data entry and the change is triggered by a change in one column which can be repeated later and can't be aggregated, while the other columns can continue changing.

In this case, you will need to LOOP over your data and detect the changes manually, as SQL doesn't have an easy way to group this kind of things. I answered a little too fast and had not noticed this.

This is best handled through a STORED PROCEDURE or a display language. I can give you the code in PHP if you'd like.

Another cheat will be to add a column that is used by GROUP BY (let's call it groubycheat) that is increased every time dtcode changes

SELECT MIN(Currentdatedtime) as Currentdatedtime, dtcode
FROM <tablename>
GROUP BY groupbycheat;

This STILL requires a LOOP to add the field, but if you need to get the results many times, then it's worth it. Otherwise ..no