Table.java 文件源码

/**
 * Create join "USING" clause.
 * <p>
 * Each of the columns specified must exist in the datasets to both the left and right
 * of the join-operator. For each pair of columns, the expression "lhs.X = rhs.X"
 * is evaluated for each row of the cartesian product as a boolean expression.
 * Only rows for which all such expressions evaluates to true are included from the
 * result set. When comparing values as a result of a USING clause, the normal rules
 * for handling affinities, collation sequences and NULL values in comparisons apply.
 * The column from the dataset on the left-hand side of the join-operator is considered
 * to be on the left-hand side of the comparison operator (=) for the purposes of
 * collation sequence and affinity precedence.
 * <p>
 * For each pair of columns identified by a USING clause, the column from the
 * right-hand dataset is omitted from the joined dataset. This is the only difference
 * between a USING clause and its equivalent ON constraint.
 *
 * @param columns
 *     Columns to use in the USING clause
 * @return Join clause
 */
@NonNull
@CheckResult
public final JoinClause using(@NonNull @Size(min = 1) final Column... columns) {
  final int colLen = columns.length;
  final StringBuilder sb = new StringBuilder(8 + colLen * 12);
  sb.append("USING (");
  for (int i = 0; i < colLen; i++) {
    if (i > 0) {
      sb.append(',');
    }
    sb.append(columns[i].name);
  }
  sb.append(')');
  return new JoinClause(this, "", sb.toString()) {
    @Override
    boolean containsColumn(@NonNull Column<?, ?, ?, ?, ?> column) {
      for (int i = 0; i < colLen; i++) {
        if (columns[i].equals(column)) {
          return true;
        }
      }
      return false;
    }
  };
}