public static void processNotNullConstraints(TableName tableName, ASTNode child, List<String> columnNames,
      List<SQLNotNullConstraint> notNullConstraints) throws SemanticException {
    List<ConstraintInfo> notNullInfos = generateConstraintInfos(child, columnNames, null, null);
    constraintInfosToNotNullConstraints(tableName, notNullInfos, notNullConstraints);
  }
Process the unique constraints from the ast node and populate the SQLUniqueConstraint list.
ql/src/java/org/apache/hadoop/hive/ql/ddl/table/constraint/ConstraintsUtils.java