public static void processDefaultConstraints(TableName tableName, ASTNode child, List<String> columnNames,
      List<SQLDefaultConstraint> defaultConstraints, final ASTNode typeChild, TokenRewriteStream tokenRewriteStream)
          throws SemanticException {
    List<ConstraintInfo> defaultInfos = generateConstraintInfos(child, columnNames, typeChild, tokenRewriteStream);
    constraintInfosToDefaultConstraints(tableName, defaultInfos, defaultConstraints);
  }
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