Thanks for replying
dwain.c I hadn't thought of that
Jeff There are no pre-existing triggers.
I tried the periodical job but it takes ages to run. I'd expected first time to run to take ages as many rows had non blank column values. I suspect even the second run would take a long time: The columns are not part of an index and some of the columns are TEXT datatype
and default to '' which I can leave in.
so
UPDATE tbl###
SET Fld1= NULL, Fld2=NULL, Fld3=NULL
WHERE Fld1 IS NOT NULL OR Fld2 IS NOT NULL OR datalength(Fld3) <> 0
I use
datalength(Fld3) <> 0
because I don't mind if the TEXT field Fld3 = ''.