Question:
i have below code to set column edit type to select 
$dg -> set_col_edittype("status", "select", "1:Open;2:Closed;3:WIP");
When any row is selected, it allows me to select one of above values. 

However when the grid loads the column shows blank values, i.e. it does not display pre-existing values in database.

Solution:
Add a blank to your key value pair string with a leading colon and semicolon.

For example:
":;1:Open;2:Closed;3:WIP"

Using SQL SELECT query? Please refer to this KB: 
https://phpgrid.uservoice.com/knowledgebase/articles/322971-create-edit-type-select-options-manually-from-s