ALTER IGNORE TABLE mytbl ADD UNIQUE (columnName);
This will make a filed a unique index but the command deletes all rows with an empty value, is there any way I can avoid that happening. The field may have NULL values if that helps.
ALTER IGNORE TABLE mytbl ADD UNIQUE (columnName);
This will make a filed a unique index but the command deletes all rows with an empty value, is there any way I can avoid that happening. The field may have NULL values if that helps.
Set the "empty" (?) values to NULL and don't use
IGNORE
. The purpose ofALTER IGNORE
is to remove duplicate values. Multiple NULL are not duplicates of each other, since the expressionNULL = NULL
is not true (and is also not false).