SelectListColumnResolver.java

/*
 * Copyright 2014-2015 the original author or authors
 *
 * Licensed 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 com.wplatform.ddal.command.dml;

import java.util.ArrayList;

import com.wplatform.ddal.command.expression.Expression;
import com.wplatform.ddal.command.expression.ExpressionColumn;
import com.wplatform.ddal.dbobject.table.Column;
import com.wplatform.ddal.dbobject.table.ColumnResolver;
import com.wplatform.ddal.dbobject.table.TableFilter;
import com.wplatform.ddal.value.Value;

/**
 * This class represents a column resolver for the column list of a SELECT
 * statement. It is used to resolve select column aliases in the HAVING clause.
 * Example:
 * <p>
 * SELECT X/3 AS A, COUNT(*) FROM SYSTEM_RANGE(1, 10) GROUP BY A HAVING A>2;
 * </p>
 *
 * @author Thomas Mueller
 */
public class SelectListColumnResolver implements ColumnResolver {

    private final Select select;
    private final Expression[] expressions;
    private final Column[] columns;

    SelectListColumnResolver(Select select) {
        this.select = select;
        int columnCount = select.getColumnCount();
        columns = new Column[columnCount];
        expressions = new Expression[columnCount];
        ArrayList<Expression> columnList = select.getExpressions();
        for (int i = 0; i < columnCount; i++) {
            Expression expr = columnList.get(i);
            Column column = new Column(expr.getAlias(), Value.NULL);
            column.setTable(null, i);
            columns[i] = column;
            expressions[i] = expr.getNonAliasExpression();
        }
    }

    @Override
    public Column[] getColumns() {
        return columns;
    }

    @Override
    public String getSchemaName() {
        return null;
    }

    @Override
    public Select getSelect() {
        return select;
    }

    @Override
    public Column[] getSystemColumns() {
        return null;
    }

    @Override
    public Column getRowIdColumn() {
        return null;
    }

    @Override
    public String getTableAlias() {
        return null;
    }

    @Override
    public TableFilter getTableFilter() {
        return null;
    }

    @Override
    public Value getValue(Column column) {
        return null;
    }

    @Override
    public Expression optimize(ExpressionColumn expressionColumn, Column column) {
        return expressions[column.getColumnId()];
    }

}