core/src/main/java/org/apache/calcite/sql/dialect/ClickHouseSqlDialect.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.config.NullCollation;
import org.apache.calcite.rel.type.RelDataType;
import org.apache.calcite.sql.SqlAbstractDateTimeLiteral;
import org.apache.calcite.sql.SqlBasicTypeNameSpec;
import org.apache.calcite.sql.SqlCall;
import org.apache.calcite.sql.SqlDataTypeSpec;
import org.apache.calcite.sql.SqlDateLiteral;
import org.apache.calcite.sql.SqlDialect;
import org.apache.calcite.sql.SqlLiteral;
import org.apache.calcite.sql.SqlNode;
import org.apache.calcite.sql.SqlTimeLiteral;
import org.apache.calcite.sql.SqlTimestampLiteral;
import org.apache.calcite.sql.SqlWriter;
import org.apache.calcite.sql.fun.SqlStdOperatorTable;
import org.apache.calcite.sql.parser.SqlParserPos;
import org.apache.calcite.sql.type.BasicSqlType;
import org.apache.calcite.sql.type.SqlTypeName;
import org.apache.calcite.util.RelToSqlConverterUtil;

import org.checkerframework.checker.nullness.qual.Nullable;

import static java.util.Objects.requireNonNull;

/**
 * A <code>SqlDialect</code> implementation for the ClickHouse database.
 */
public class ClickHouseSqlDialect extends SqlDialect {
  public static final SqlDialect.Context DEFAULT_CONTEXT = SqlDialect.EMPTY_CONTEXT
      .withDatabaseProduct(SqlDialect.DatabaseProduct.CLICKHOUSE)
      .withIdentifierQuoteString("`")
      .withNullCollation(NullCollation.LOW);

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

  /** Creates a ClickHouseSqlDialect. */
  public ClickHouseSqlDialect(Context context) {
    super(context);
  }

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

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

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

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

  @Override public CalendarPolicy getCalendarPolicy() {
    return CalendarPolicy.SHIFT;
  }

  @Override public @Nullable SqlNode getCastSpec(RelDataType type) {
    if (type instanceof BasicSqlType) {
      SqlTypeName typeName = type.getSqlTypeName();
      switch (typeName) {
      case VARCHAR:
        return createSqlDataTypeSpecByName("String", typeName);
      case TINYINT:
        return createSqlDataTypeSpecByName("Int8", typeName);
      case SMALLINT:
        return createSqlDataTypeSpecByName("Int16", typeName);
      case INTEGER:
        return createSqlDataTypeSpecByName("Int32", typeName);
      case BIGINT:
        return createSqlDataTypeSpecByName("Int64", typeName);
      case FLOAT:
        return createSqlDataTypeSpecByName("Float32", typeName);
      case DOUBLE:
        return createSqlDataTypeSpecByName("Float64", typeName);
      case DATE:
        return createSqlDataTypeSpecByName("Date", typeName);
      case TIMESTAMP:
      case TIMESTAMP_WITH_LOCAL_TIME_ZONE:
        return createSqlDataTypeSpecByName("DateTime", typeName);
      default:
        break;
      }
    }

    return super.getCastSpec(type);
  }

  private static SqlDataTypeSpec createSqlDataTypeSpecByName(String typeAlias,
      SqlTypeName typeName) {
    SqlBasicTypeNameSpec spec = new SqlBasicTypeNameSpec(typeName, SqlParserPos.ZERO) {
      @Override public void unparse(SqlWriter writer, int leftPrec, int rightPrec) {
        // unparse as an identifier to ensure that type names are cased correctly
        writer.identifier(typeAlias, true);
      }
    };
    return new SqlDataTypeSpec(spec, SqlParserPos.ZERO);
  }

  @Override public void unparseDateTimeLiteral(SqlWriter writer,
      SqlAbstractDateTimeLiteral literal, int leftPrec, int rightPrec) {
    String toFunc;
    if (literal instanceof SqlDateLiteral) {
      toFunc = "toDate";
    } else if (literal instanceof SqlTimestampLiteral) {
      toFunc = "toDateTime";
    } else if (literal instanceof SqlTimeLiteral) {
      toFunc = "toTime";
    } else {
      throw new RuntimeException("ClickHouse does not support DateTime literal: "
          + literal);
    }

    writer.literal(toFunc + "('" + literal.toFormattedString() + "')");
  }

  @Override public void unparseOffsetFetch(SqlWriter writer, @Nullable SqlNode offset,
      @Nullable SqlNode fetch) {
    requireNonNull(fetch, "fetch");

    writer.newlineAndIndent();
    final SqlWriter.Frame frame =
        writer.startList(SqlWriter.FrameTypeEnum.FETCH);
    writer.keyword("LIMIT");

    if (offset != null) {
      offset.unparse(writer, -1, -1);
      writer.sep(",", true);
    }

    fetch.unparse(writer, -1, -1);
    writer.endList(frame);
  }

  @Override public void unparseCall(SqlWriter writer, SqlCall call,
      int leftPrec, int rightPrec) {
    if (call.getOperator() == SqlStdOperatorTable.SUBSTRING) {
      RelToSqlConverterUtil.specialOperatorByName("substring")
          .unparse(writer, call, 0, 0);
    } else {
      switch (call.getKind()) {
      case FLOOR:
        if (call.operandCount() != 2) {
          super.unparseCall(writer, call, leftPrec, rightPrec);
          return;
        }

        unparseFloor(writer, call);
        break;

      case COUNT:
        // CH returns NULL rather than 0 for COUNT(DISTINCT) of NULL values.
        // https://github.com/yandex/ClickHouse/issues/2494
        // Wrap the call in a CH specific coalesce (assumeNotNull).
        if (call.getFunctionQuantifier() != null
            && call.getFunctionQuantifier().toString().equals("DISTINCT")) {
          writer.print("assumeNotNull");
          SqlWriter.Frame frame = writer.startList("(", ")");
          super.unparseCall(writer, call, leftPrec, rightPrec);
          writer.endList(frame);
        } else {
          super.unparseCall(writer, call, leftPrec, rightPrec);
        }
        break;

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

  /**
   * Unparses datetime floor for ClickHouse.
   *
   * @param writer Writer
   * @param call Call
   */
  private static void unparseFloor(SqlWriter writer, SqlCall call) {
    final SqlLiteral timeUnitNode = call.operand(1);
    TimeUnitRange unit = timeUnitNode.getValueAs(TimeUnitRange.class);

    String funName;
    switch (unit) {
    case YEAR:
      funName = "toStartOfYear";
      break;
    case MONTH:
      funName = "toStartOfMonth";
      break;
    case WEEK:
      funName = "toMonday";
      break;
    case DAY:
      funName = "toDate";
      break;
    case HOUR:
      funName = "toStartOfHour";
      break;
    case MINUTE:
      funName = "toStartOfMinute";
      break;
    default:
      throw new RuntimeException("ClickHouse does not support FLOOR for time unit: "
          + unit);
    }

    writer.print(funName);
    SqlWriter.Frame frame = writer.startList("(", ")");
    call.operand(0).unparse(writer, 0, 0);
    writer.endList(frame);
  }
}