sql - Insert new row if value present in column -

i need check if column value exists record, , if insert duplicate of record, 1 of fields updated.

the fields inccodes table are chars:

incomecode, description, location, costcentre, newincomecode 

i have sql command updates of incomecodes newincomecode , clears newincomecode column present:

update inccodes  set incomecode = newincomecode    ,newincomecode = '' newincomecode <> ''   , location = location1 

however need command same thing except instead of updating incomecode field, creates duplicate record incomecode updated newincomecode field. pseudo sql:

insert inccodes values (select newincomecode               ,description               ,location               ,costcentre               ,null         inccodes         newincomecode <> '') 

any advice appreciated. can see similar questions insert based on criteria nothing need.

thanks in advance.

insert ignore inccodes     (incomecode, description, location, costcentre, newincomecode) select     newincomecode, description, location, costcentre, '' inccodes newincomecode <> '' , location = location1 ;