[SQL] How can I quit this: "Unique " to my table?

Hello pgsql-sql, When my table was create I wrote this: MyDatabase=# create table b_prestamo(no_inventa char(16) unique not null, cve_area char(10), date1 date); I need now that my table can accept repeated records, but not Null. How can I do that? SomeBody can help me please? My ta

[SQL]

I have a period of consultation with Fecha1 and Fecha2 and two tables with the follow data: Table1 |Clave_activo | Cantidad | fecha | | | | | | clave1 |5 | 01/02/00 | | clave3 |7 | 05/05/01 | | clave1 |2 | 03/09/