1) Make sure that the column only conains unique values lets assume we are working with a table called t5. it has two columns. id ( the primary key ) and name. To find out if the column contains any duplicate values make the following statements.
select name from t5 ; select distinct name from t5 ;
IF the row counts are the same then the column contains unique values only.
2) Create a unique index as follows..
alter table t5 add unique ( name ) ;
If you want to give the index a name do it this way...
alter table t5 add unique namedex ( name )
3) Drink a beer
* You may optionally drink beer between and during steps one and two.