How can change the datatype of a field in saleslogix database without dropping it and loosing all the data ?

SLX Doesn't store the data type anywhere. It knows what the datatype is by querying the db at runtime in order to know etc. So, you can simply change this via ALTER TABLE X ALTER COLUMN COL1 VARCHAR(20) NULL for example. Once this is done, restart the slxserver service and that change is then picked up (hint: if you don't want to do the restart, add a dummy field in Architect to any table and then commit/drop it). You can also add the above as a SQL Command and bundle it for installation to a live site. You can, even, if you have a single site, no remotes, don't use sync etc. just change it via SQL Studio.

Obviously, all rules about conversion of 1 datatype to another prevals. You can't convert a varchar to inteteger without potentially losing data for example.

Worked like a charm, I just had repopulate the DBManager and showed the change, since was change for Web Client, had to remove the field from Entity in Application Architect, rebuild interfaces >> Re-Add the field whose datatype was changed and reflected change for Entity in Web.

Else you get a type mismatch error if changes are not made in Application Architect.

And in the web client there might be some control issues in a form......