core/src/main/java/org/apache/calcite/sql/dialect/HsqldbSqlDialect.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to you under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.calcite.sql.dialect;

import org.apache.calcite.avatica.util.TimeUnitRange;
import org.apache.calcite.sql.SqlBasicCall;
import org.apache.calcite.sql.SqlCall;
import org.apache.calcite.sql.SqlDialect;
import org.apache.calcite.sql.SqlLiteral;
import org.apache.calcite.sql.SqlNode;
import org.apache.calcite.sql.SqlNodeList;
import org.apache.calcite.sql.SqlWriter;
import org.apache.calcite.sql.fun.SqlCase;
import org.apache.calcite.sql.fun.SqlFloorFunction;
import org.apache.calcite.sql.fun.SqlStdOperatorTable;
import org.apache.calcite.sql.parser.SqlParserPos;

/**
 * A <code>SqlDialect</code> implementation for the Hsqldb database.
 */
public class HsqldbSqlDialect extends SqlDialect {
  public static final SqlDialect.Context DEFAULT_CONTEXT = SqlDialect.EMPTY_CONTEXT
      .withDatabaseProduct(SqlDialect.DatabaseProduct.HSQLDB);

  public static final SqlDialect DEFAULT = new HsqldbSqlDialect(DEFAULT_CONTEXT);

  /** Creates an HsqldbSqlDialect. */
  public HsqldbSqlDialect(Context context) {
    super(context);
  }

  @Override public boolean supportsCharSet() {
    return false;
  }

  @Override public boolean supportsWindowFunctions() {
    return false;
  }

  @Override public void unparseCall(SqlWriter writer, SqlCall call,
      int leftPrec, int rightPrec) {
    switch (call.getKind()) {
    case FLOOR:
      if (call.operandCount() != 2) {
        super.unparseCall(writer, call, leftPrec, rightPrec);
        return;
      }

      final SqlLiteral timeUnitNode = call.operand(1);
      final TimeUnitRange timeUnit = timeUnitNode.getValueAs(TimeUnitRange.class);

      final String translatedLit = convertTimeUnit(timeUnit);
      SqlCall call2 = SqlFloorFunction.replaceTimeUnitOperand(call, translatedLit,
          timeUnitNode.getParserPosition());
      SqlFloorFunction.unparseDatetimeFunction(writer, call2, "TRUNC", true);
      break;

    default:
      super.unparseCall(writer, call, leftPrec, rightPrec);
    }
  }

  @Override public void unparseOffsetFetch(SqlWriter writer, SqlNode offset,
      SqlNode fetch) {
    unparseFetchUsingLimit(writer, offset, fetch);
  }

  @Override public SqlNode rewriteSingleValueExpr(SqlNode aggCall) {
    final SqlNode operand = ((SqlBasicCall) aggCall).operand(0);
    final SqlLiteral nullLiteral = SqlLiteral.createNull(SqlParserPos.ZERO);
    final SqlNode unionOperand = SqlStdOperatorTable.VALUES.createCall(SqlParserPos.ZERO,
        SqlLiteral.createApproxNumeric("0", SqlParserPos.ZERO));
    // For hsqldb, generate
    //   CASE COUNT(*)
    //   WHEN 0 THEN NULL
    //   WHEN 1 THEN MIN(<result>)
    //   ELSE (VALUES 1 UNION ALL VALUES 1)
    //   END
    final SqlNode caseExpr =
        new SqlCase(SqlParserPos.ZERO,
            SqlStdOperatorTable.COUNT.createCall(SqlParserPos.ZERO, operand),
            SqlNodeList.of(
                SqlLiteral.createExactNumeric("0", SqlParserPos.ZERO),
                SqlLiteral.createExactNumeric("1", SqlParserPos.ZERO)),
            SqlNodeList.of(
                nullLiteral,
                SqlStdOperatorTable.MIN.createCall(SqlParserPos.ZERO, operand)),
            SqlStdOperatorTable.SCALAR_QUERY.createCall(SqlParserPos.ZERO,
                SqlStdOperatorTable.UNION_ALL
                    .createCall(SqlParserPos.ZERO, unionOperand, unionOperand)));

    LOGGER.debug("SINGLE_VALUE rewritten into [{}]", caseExpr);

    return caseExpr;
  }

  private static String convertTimeUnit(TimeUnitRange unit) {
    switch (unit) {
    case YEAR:
      return "YYYY";
    case MONTH:
      return "MM";
    case DAY:
      return "DD";
    case WEEK:
      return "WW";
    case HOUR:
      return "HH24";
    case MINUTE:
      return "MI";
    case SECOND:
      return "SS";
    default:
      throw new AssertionError("could not convert time unit to HSQLDB equivalent: "
          + unit);
    }
  }
}

// End HsqldbSqlDialect.java