Role of the datatable primary key in the dataadapter. Fill Method

If the datatable does not have a primary key, the retrieved record rows and columns are added to the current datatable after the fill method.

You can specify a primary key in either of the following ways:

(1) set da. missingschemaaction = system. Data. missingschemaaction. addwithkey. The default value is add.

(2) define the primary key constraint of the data table after the first fill

Da. Fill (DS, "author ");
DS. Tables [0]. primarykey = new datacolumn [] {Ds. Tables [0]. Columns [0]};

In this way, the dataset will be updated with the data primary key after fill, instead of simply appending.