jdbcdatabasemetadata.java

一个用java写的开源的数据库系统

/* Copyrights and Licenses
 *
 * This product includes Hypersonic SQL.
 * Originally developed by Thomas Mueller and the Hypersonic SQL Group. 
 *
 * Copyright (c) 1995-2000 by the Hypersonic SQL Group. All rights reserved. 
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 * provided that the following conditions are met: 
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 *         and the following disclaimer. 
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 *        following acknowledgment: "This product includes Hypersonic SQL." 
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 *        "Hypersonic SQL" appear in their names without prior written permission of the
 *         Hypersonic SQL Group. 
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 *          product includes Hypersonic SQL." 
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 * not limited to, the implied warranties of merchantability and fitness for a particular purpose are
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 * This software consists of voluntary contributions made by many individuals on behalf of the
 * Hypersonic SQL Group.
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 *
 * For work added by the HSQL Development Group:
 *
 * Copyright (c) 2001-2002, The HSQL Development Group
 * All rights reserved.
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 * modification, are permitted provided that the following conditions are met:
 *
 * Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer, including earlier
 * license statements (above) and comply with all above license conditions.
 *
 * Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
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 *
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 * contributors may be used to endorse or promote products derived from this
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 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */


package org.hsqldb;

import org.hsqldb.lib.StringUtil;
import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.ResultSet;
import java.sql.SQLException;

// fredt@users 20020320 - patch 1.7.0 - JDBC 2 support and error trapping
// JDBC 2 methods can now be called from jdk 1.1.x - see javadoc comments
// boucherb@users 20020509 - added "throws SQLException" to all methods where
// it was missing here but specified in the java.sql.DatabaseMetaData interface,
// updated generic documentation to JDK 1.4, and added JDBC3 methods and docs
// boucherb@users and fredt@users 20020409/20020505 extensive review and update
// of docs and behaviour to comply with previous and latest java.sql specification

/**
 * Comprehensive information about the database as a whole.
 * <P>
 * This interface is implemented by driver vendors to let users know the capabilities
 * of a Database Management System (DBMS) in combination with
 * the driver based on JDBC<sup><font size=-2>TM</font></sup> technology
 * ("JDBC driver") that is used with it.  Different relational DBMSs often support
 * different features, implement features in different ways, and use different
 * data types.  In addition, a driver may implement a feature on top of what the
 * DBMS offers.  Information returned by methods in this interface applies
 * to the capabilities of a particular driver and a particular DBMS working
 * together. Note that as used in this documentation, the term "database" is
 * used generically to refer to both the driver and DBMS.
 * <P>
 * A user for this interface is commonly a tool that needs to discover how to
 * deal with the underlying DBMS.  This is especially true for applications
 * that are intended to be used with more than one DBMS. For example, a tool might use the method
 * <code>getTypeInfo</code> to find out what data types can be used in a
 * <code>CREATE TABLE</code> statement.  Or a user might call the method
 * <code>supportsCorrelatedSubqueries</code> to see if it is possible to use
 * a correlated subquery or <code>supportsBatchUpdates</code> to see if it is
 * possible to use batch updates.
 * <P>
 * Some <code>DatabaseMetaData</code> methods return lists of information
 * in the form of <code>ResultSet</code> objects.
 * Regular <code>ResultSet</code> methods, such as
 * <code>getString</code> and <code>getInt</code>, can be used
 * to retrieve the data from these <code>ResultSet</code> objects.  If
 * a given form of metadata is not available, the <code>ResultSet</code>
 * getter methods throw an <code>SQLException</code>.
 * <P>
 * Some <code>DatabaseMetaData</code> methods take arguments that are
 * String patterns.  These arguments all have names such as fooPattern.
 * Within a pattern String, "%" means match any substring of 0 or more
 * characters, and "_" means match any one character. Only metadata
 * entries matching the search pattern are returned. If a search pattern
 * argument is set to <code>null</code>, that argument's criterion will
 * be dropped from the search.
 * <P>
 * A method that gets information about a feature that the driver does not
 * support will throw an <code>SQLException</code>.
 * In the case of methods that return a <code>ResultSet</code>
 * object, either a <code>ResultSet</code> object (which may be empty) is
 * returned or an <code>SQLException</code> is thrown.<p>
 *
 * <!-- start release-specific documentation -->
 * <span class="ReleaseSpecificDocumentation">
 * <b>HSQLDB-Specific Information:</b> <p>
 *
 * <b>JRE 1.1.x Notes:</b> <p>
 *
 * In general, JDBC 2 support requires Java 1.2 and above, and JDBC3 requires
 * Java 1.4 and above. In HSQLDB, support for methods introduced in different
 * versions of JDBC depends on the JDK version used for compiling and building
 * HSQLDB.<p>
 *
 * Since 1.7.0, it is possible to build the product so that
 * all JDBC 2 methods can be called while executing under the version 1.1.x
 * <em>Java Runtime Environment</em><sup><font size="-2">TM</font></sup>.
 * However, some of these method calls require <code>int</code> values that
 * are defined only in the JDBC 2 or greater version of
 * <a href="http://java.sun.com/j2se/1.4/docs/api/java/sql/ResultSet.html">
 * <CODE>ResultSet</CODE></a> interface.  For this reason, when the
 * product is compiled under JDK 1.1.x, these values are defined in
 * {@link jdbcResultSet jdbcResultSet}.<p>
 *
 * In a JRE 1.1.x environment, calling JDBC 2 methods that take or return the
 * JDBC2-only <CODE>ResultSet</CODE> values can be achieved by referring
 * to them in parameter specifications and return value comparisons,
 * respectively, as follows: <p>
 *
 * <CODE class="JavaCodeExample">
 * dbcResultSet.FETCH_FORWARD<br>
 * jdbcResultSet.TYPE_FORWARD_ONLY<br>
 * jdbcResultSet.TYPE_SCROLL_INSENSITIVE<br>
 * jdbcResultSet.CONCUR_READ_ONLY<br>
 * </CODE> <p>
 *
 * However, please note that code written in such a manner will not be
 * compatible for use with other JDBC 2 drivers, since they expect and use
 * <code>ResultSet</code>, rather than <code>jdbcResultSet</code>.  Also
 * note, this feature is offered solely as a convenience to developers
 * who must work under JDK 1.1.x due to operating constraints, yet wish to
 * use some of the more advanced features available under the JDBC 2
 * specification.<p>
 *
 * (fredt@users)<br>
 * (boucherb@users)<p>
 *
 * </span>
 * <!-- end release-specific documentation -->
 */
public class jdbcDatabaseMetaData implements java.sql.DatabaseMetaData {

    /**
     * The connection this object uses to retrieve instance-specific metadata.
     */
    private jdbcConnection cConnection;

    //----------------------------------------------------------------------
    // First, a variety of minor information about the target database.

    /**
     * Retrieves whether the current user can call all the procedures
     * returned by the method <code>getProcedures</code>.  <p>
     *
     * <!-- start release-specific documentation -->
     * <span class="ReleaseSpecificDocumentation">
     * <b>HSQLDB-Specific Information:</b> <p>
     *
     * Up to and including 1.7.1, HSQLDB does not return any rows from
     * <code>getProcedures</code>.  However,
     * <code>allProceduresAreCallable</code> always returns <code>true</code>.
     * This is simply meant to indicate that all users can call all stored
     * procedures made available by default in a newly created HSQLDB
     * database.
     * </span>
     * <!-- end release-specific documentation -->
     *
     * @return <code>true</code> if so; <code>false</code> otherwise
     * @exception SQLException if a database access error occurs
     */
    public boolean allProceduresAreCallable() throws SQLException {

        if (Trace.TRACE) {
            Trace.trace();
        }

        return true;
    }

    /**
     * Retrieves whether the current user can use all the tables returned
     * by the method <code>getTables</code> in a <code>SELECT</code>
     * statement.  <p>
     *
     * <!-- start release-specific documentation -->
     * <span class="ReleaseSpecificDocumentation">
     * <b>HSQLDB-Specific Information:</b> <p>
     *
     * Up to and including 1.7.1, HSQLDB will, by default, throw an exception
     * for any non-admin user calling <code>getTables</code>, while any
     * admin user can <CODE>SELECT</CODE> from any table.  As such, this
     * method always returns <code>true</code>.  However, if an admin user
     * grants <CODE>SELECT</CODE> access to <CODE>SYSTEM_TABLES</CODE> to
     * a non-admin user, then it is possible for that user to be denied
     * <CODE>SELECT</CODE> access to tables listed when he/she calls
     * <code>getTables</code>.  This behaviour will be corrected in 1.7.2. <p>
     *
     * </span>
     * <!-- end release-specific documentation -->
     *
     *
     * @return <code>true</code> if so; <code>false</code> otherwise
     * @exception SQLException if a database access error occurs
     */
    public boolean allTablesAreSelectable() throws SQLException {

        if (Trace.TRACE) {
            Trace.trace();
        }

        return true;
    }

    /**
     * Retrieves the URL for this DBMS.
     *
     *
     * @return the URL for this DBMS or <code>null</code> if it cannot be
     *         generated
     * @exception SQLException if a database access error occurs
     */
    public String getURL() throws SQLException {

        if (Trace.TRACE) {
            Trace.trace();
        }

        // CHECKME:
        // is this always correct?
        // boucherb@users 20020426
        return "jdbc:hsqldb:" + cConnection.getName();
    }

    /**
     * Retrieves the user name as known to this database.
     *
     *
     * @return the database user name
     * @exception SQLException if a database access error occurs
     */
    public String getUserName() throws SQLException {

        if (Trace.TRACE) {
            Trace.trace();
        }

        ResultSet r = executeSelect("SYSTEM_CONNECTIONINFO", "KEY='USER'");

        r.next();

        return r.getString(2);
    }

    /**
     * Retrieves whether this database is in read-only mode. <p>
     *
     * <!-- start release-specific documentation -->
     * <span class="ReleaseSpecificDocumentation">
     * <b>HSQLDB-Specific Information:</b> <p>
     *
     * Up to and including 1.7.1, this is a synonym for
     * {@link jdbcConnection#isReadOnly()} and does not report on
     * the global read-only state of the database.  This behaviour
     * will be corrected in 1.7.2.
     * </span>
     * <!-- end release-specific documentation -->
     *
     *
     * @return <code>true</code> if so; <code>false</code> otherwise
     * @exception SQLException if a database access error occurs
     */
    public boolean isReadOnly() throws SQLException {

        if (Trace.TRACE) {
            Trace.trace();
        }

        // FIXME:
        // This is wrong.  This should determine if the
        // whole database is in read-only mode, not whether the
        // connection to the database is in read only mode.
        // That is why there is Connection.isReadOnly() and
        // DatabaseMetaData.isReadOnly().
        // boucherb@users 20020426
        // fredt@users - sure, let's get the correct value for 1.7.1
        return cConnection.isReadOnly();
    }

    /**
     * Retrieves whether <code>NULL</code> values are sorted high.
     * Sorted high means that <code>NULL</code> values
     * sort higher than any other value in a domain.  In an ascending order,
     * if this method returns <code>true</code>,  <code>NULL</code> values
     * will appear at the end. By contrast, the method
     * <code>nullsAreSortedAtEnd</code> indicates whether <code>NULL</code> values
     * are sorted at the end regardless of sort order. <p>
     *
     * <!-- start release-specific documentation -->
     * <span class="ReleaseSpecificDocumentation">
     * <b>HSQLDB-Specific Information:</b> <p>
     *
     * HSQLDB sorts null low; this method always returns <code>false</code>.
     * </span>
     * <!-- end release-specific documentation -->
     *
     *
     * @return <code>true</code> if so; <code>false</code> otherwise
     * @exception SQLException if a database access error occurs
     */
    public boolean nullsAreSortedHigh() throws SQLException {

        if (Trace.TRACE) {
            Trace.trace();
        }

        return false;
    }

    /**
     * Retrieves whether <code>NULL</code> values are sorted low.
     * Sorted low means that <code>NULL</code> values
     * sort lower than any other value in a domain.  In an ascending order,
     * if this method returns <code>true</code>,  <code>NULL</code> values
     * will appear at the beginning. By contrast, the method
     * <code>nullsAreSortedAtStart</code> indicates whether <code>NULL</code> values
     * are sorted at the beginning regardless of sort order. <p>
     *
     * <!-- start release-specific documentation -->
     * <span class="ReleaseSpecificDocumentation">
     * <b>HSQLDB-Specific Information:</b> <p>
     *
     * HSQLDB sorts null low; this method always returns <code>true</code>.
     * </span>
     * <!-- end release-specific documentation -->
     *
     *
     * @return <code>true</code> if so; <code>false</code> otherwise
     * @exception SQLException if a database access error occurs
     */
    public boolean nullsAreSortedLow() throws SQLException {

        if (Trace.TRACE) {
            Trace.trace();
        }

        return true;
    }

    /**
     * Retrieves whether <code>NULL</code> values are sorted at the start regardless
     * of sort order. <p>
     *
     * <!-- start release-specific documentation -->
     * <span class="ReleaseSpecificDocumentation">