MS SQL Query

Dear sirs, I need a update query for a table. The fieldname 'ex-value' must be set to 0 (zero) if the record 'id' occurs multiple times. The first time the id occurs, the value must not be changed. In this sample 'id' occurs several times thats why de 'ex-value' is in the sample table after running the update query is 0 (zero). Kind Regards, Wim Faber CURRENT TABLE table1 id name ex-value 1 AB 34 2 CD 55 3 EF 65 4 GH 77 5 IJ 5 1 KL 34 4 MN 77 3 OP 65 1 QR 34 6 ST 98 AFTER UPDATE QUERY table 1 id name ex-value 1 AB 34 2 CD 55 3 EF 65 4 GH 77 5 IJ 5 1 KL 0 4 MN 0 3 OP 0 1 QR 0 6 ST 98