content: /*
   * 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;
  
  import org.apache.calcite.rel.type.RelDataType;
  import org.apache.calcite.sql.type.OperandTypes;
  import org.apache.calcite.sql.type.ReturnTypes;
  import org.apache.calcite.sql.type.SqlTypeUtil;
  import org.apache.calcite.sql.validate.SqlValidator;
  import org.apache.calcite.sql.validate.SqlValidatorImpl;
  import org.apache.calcite.sql.validate.SqlValidatorScope;
  import org.apache.calcite.sql.validate.SqlValidatorUtil;
  
  import static org.apache.calcite.util.Static.RESOURCE;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * An operator that applies a filter before rows are included in an aggregate
   * function.
   *
   * <p>Operands are as follows:
   *
   * <ul>
   * <li>0: a call to an aggregate function ({@link SqlCall})
   * <li>1: predicate
   * </ul>
   */
  public class SqlFilterOperator extends SqlBinaryOperator {
    //~ Constructors -----------------------------------------------------------
  
    public SqlFilterOperator() {
      super("FILTER", SqlKind.FILTER, 20, true, ReturnTypes.ARG0_FORCE_NULLABLE,
          null, OperandTypes.ANY_ANY);
    }
  
    //~ Methods ----------------------------------------------------------------
  
  
    @Override public void unparse(SqlWriter writer, SqlCall call, int leftPrec,
        int rightPrec) {
      assert call.operandCount() == 2;
      final SqlWriter.Frame frame =
          writer.startList(SqlWriter.FrameTypeEnum.SIMPLE);
      call.operand(0).unparse(writer, leftPrec, getLeftPrec());
      writer.sep(getName());
      writer.sep("(");
      writer.sep("WHERE");
      call.operand(1).unparse(writer, getRightPrec(), rightPrec);
      writer.sep(")");
      writer.endList(frame);
    }
  
    @Override public void validateCall(
        SqlCall call,
        SqlValidator validator,
        SqlValidatorScope scope,
        SqlValidatorScope operandScope) {
      assert call.getOperator() == this;
      assert call.operandCount() == 2;
      final SqlValidatorUtil.FlatAggregate flat = SqlValidatorUtil.flatten(call);
      SqlCall aggCall = flat.aggregateCall;
      if (!aggCall.getOperator().isAggregator()) {
        throw validator.newValidationError(aggCall,
            RESOURCE.filterNonAggregate());
      }
      validator.validateAggregateParams(aggCall, flat.filter,
          flat.distinctList, flat.orderList, scope);
  
      final SqlNode filter = requireNonNull(flat.filter);
      final RelDataType type = validator.deriveType(scope, filter);
      if (!SqlTypeUtil.inBooleanFamily(type)) {
        throw validator.newValidationError(filter,
            RESOURCE.condMustBeBoolean("FILTER"));
      }
    }
  
    @Override public RelDataType deriveType(
        SqlValidator validator,
        SqlValidatorScope scope,
        SqlCall call) {
      // Validate type of the inner aggregate call
      validateOperands(validator, scope, call);
  
      // Assume the first operand is an aggregate call and derive its type.
      final SqlValidatorUtil.FlatAggregate flat = SqlValidatorUtil.flatten(call);
      final SqlCall aggCall = flat.aggregateCall;
  
      // Pretend that group-count is 0. This tells the aggregate function that it
      // might be invoked with 0 rows in a group. Most aggregate functions will
      // return NULL in this case.
      SqlCallBinding opBinding = new SqlCallBinding(validator, scope, aggCall) {
        @Override public boolean hasEmptyGroup() {
          return true;
        }
      };
  
      RelDataType ret = aggCall.getOperator().inferReturnType(opBinding);
  
      // Copied from validateOperands
      final SqlValidatorImpl validator1 = (SqlValidatorImpl) validator;
      validator1.setValidatedNodeType(call, ret);
      validator1.setValidatedNodeType(aggCall, ret);
      if (flat.distinctList != null) {
        validator1.setValidatedNodeType(
            requireNonNull(flat.distinctCall), ret);
      }
      if (flat.orderList != null) {
        validator1.setValidatedNodeType(
            requireNonNull(flat.orderCall), ret);
      }
      return ret;
    }
  
  }
  