title: Foreign key referenced value used only once
body: <p>I have this kind problem regarding sql:</p>
  
  <pre>Table 1: ID_1 (Primary Key) | NAME | LASTNAME | EMAIL...
  Table 2: ID_2 (Primary Key) | NAME2 | LASTNAME2 | EMAIL...</pre>
  
  <p>Normally using constraints it is possible to make as column in TABLE 2 
  (NAME 2 for example) as a foreign key for NAME the first TABLE 1.</p>
  
  <p>The general relation would be one-many. That's one value from column NAME in TABLE 1 used many times in column NAME2 in Table 2.</p>
  
  <p>Now what I want to achieve is that making the rule one-to-one, so I cannot have duplicated values of NAME from table TABLE 1 in TABLE 2. </p>
  
  <p>Does it require triggers or it can be set by constraint when creating the tables?</p>