explainplan.java

来自「非常棒的java数据库」· Java 代码 · 共 78 行

/*
 * Copyright 2004-2008 H2 Group. Licensed under the H2 License, Version 1.0
 * (http://h2database.com/html/license.html).
 * Initial Developer: H2 Group
 */
package org.h2.command.dml;

import java.sql.SQLException;

import org.h2.command.Prepared;
import org.h2.engine.Session;
import org.h2.expression.ExpressionColumn;
import org.h2.result.LocalResult;
import org.h2.table.Column;
import org.h2.util.ObjectArray;
import org.h2.value.Value;
import org.h2.value.ValueString;

/**
 * This class represents the statement
 * EXPLAIN
 */
public class ExplainPlan extends Prepared {

    private Prepared command;
    private LocalResult result;

    public ExplainPlan(Session session) {
        super(session);
    }

    public void setCommand(Prepared command) {
        this.command = command;
    }

    public void prepare() throws SQLException {
        command.prepare();
    }

    public LocalResult queryMeta() throws SQLException {
        return query(-1);
    }

    public LocalResult query(int maxrows) throws SQLException {
        // TODO rights: are rights required for explain?
        ObjectArray expressions = new ObjectArray();
        Column column = new Column("PLAN", Value.STRING);
        ExpressionColumn expr = new ExpressionColumn(session.getDatabase(), column);
        expressions.add(expr);
        result = new LocalResult(session, expressions, 1);
        if (maxrows >= 0) {
            String plan = command.getPlanSQL();
            add(plan);
        }
        result.done();
        return result;
    }

    private void add(String text) throws SQLException {
        Value[] row = new Value[1];
        Value value = ValueString.get(text);
        row[0] = value;
        result.addRow(row);
    }

    public boolean isQuery() {
        return true;
    }

    public boolean isTransactional() {
        return true;
    }

    public boolean isReadOnly() {
        return true;
    }
}