title: Adding the NOT_NULL constraint to an SQL column
body: <p>I'm trying to add the NOT_NULL constraint to a column in an SQL h2 database, using</p>
  
  <pre><code>ALTER TABLE CHARACTERS ADD CONSTRAINT nn_PID NOT_NULL (PLAYER_ID);
  </code></pre>
  
  <p>This follows the pattern I found <a href="http://www.w3schools.com/sql/sql_primarykey.asp" rel="noreferrer">here</a>:</p>
  
  <pre><code>ALTER TABLE Persons ADD CONSTRAINT pk_PersonID PRIMARY KEY (P_Id,LastName)
  </code></pre>
  
  <p>Except I change the constraint, table and column names. But I get this error:</p>
  
  <blockquote>
    <p>Syntax error in SQL statement "ALTER TABLE CHARACTERS ADD CONSTRAINT NN_PID NOT_NULL[*] (PLAYER_ID) "; expected "., COMMENT, PRIMARY, INDEX, KEY, CHECK, UNIQUE, FOREIGN"; SQL statement:
    ALTER TABLE CHARACTERS ADD CONSTRAINT nn_PID NOT_NULL (PLAYER_ID) [42001-168] 42001/42001 (Help) </p>
  </blockquote>
  
  <p>How can I add the NOT_NULL constraint?</p>