Quadcap Embeddable Database

com/quadcap/sql/StmtDropColumn.java

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package com.quadcap.sql;

/* Copyright 1999 - 2003 Quadcap Software.  All rights reserved.
 *
 * This software is distributed under the Quadcap Free Software License.
 * This software may be used or modified for any purpose, personal or
 * commercial.  Open Source redistributions are permitted.  Commercial
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 * this software requires a "Commercial Redistribution License"; see
 * http://www.quadcap.com/purchase.
 *
 * Redistributions qualify as "Open Source" under  one of the following terms:
 *   
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 *    materials and delivery.
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 *    Redistributions are accompanied by a copy of the Source Code or by an
 *    irrevocable offer to provide a copy of the Source Code for up to three
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 *    must allow further use, modification, and redistribution of the Source
 *    Code under substantially the same terms as this license.
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import java.io.IOException;

import java.util.List;

import java.sql.SQLException;

import com.quadcap.sql.file.BlockFile;
import com.quadcap.sql.file.ByteUtil;

import com.quadcap.sql.index.BCursor;
import com.quadcap.sql.index.Btree;

import com.quadcap.sql.types.Value;
import com.quadcap.sql.types.ValueNull;

import com.quadcap.util.Debug;

/**
 * Implementation of SQL <b>ALTER TABLE DROP COLUMN</b> statement.
 *
 * @author Stan Bailes
 */
public class StmtDropColumn implements Stmt {
    String                              tableName;
    String                              colName;

    /**
     * Explicit constructor from table name and column name
     */
    public StmtDropColumn(String tableName, String colName) {
        this.tableName = tableName;
        this.colName = colName;
    }

    /**
     * Delete any constraints which reference the specified column.
     * Reset all other constraint column maps.
     *
     * @param col one-based column number
     */
    public void deleteColumnConstraints(Session session, Table table, int col)
        throws SQLException, IOException
    {
        int num = table.getNumConstraints();

        // Copy constraints for stable enumeration
        Constraint[] tmpC = new Constraint[num];
        for (int i = 0; i < num; i++) {
            tmpC[i] = table.getConstraint(i);
        }
        for (int i = 0; i < num; i++) {
            Constraint con = tmpC[i];
            int[] cols = con.getColumns();
            boolean match = false;
            for (int j = 0; j < cols.length && !match; j++) {
                match = cols[j] == col;
            }
            if (match) {
                session.doStep(new DeleteConstraint(session, table, con));
            } else {
                con.resetColumns();
            }
        }
    }

    /**
     * Stmt.execute()
     *
     * For DROP COLUMN, we need to update the table definition, of course.
     * But then, we need to update *all* of the rows!
     */
    public void execute(Session session) throws IOException, SQLException {
        // First, acquire the schema and table locks       
        Database db = session.getDatabase();
        session.getTableWriteLock("#Schema");
        session.getTableWriteLock(tableName);

        Table table = (Table)db.getRelation(tableName);
        //#ifdef DEBUG
        if (table == null) {
            throw new SQLException("No table: " + tableName);
        }
        //#endif
        Column column = table.getColumn(colName);

        // Drop all the column's constraints first
        List constraints = column.getConstraints();
        if (constraints != null) {
            for (int i = 0; i < constraints.size(); i++) {
                Constraint constraint = (Constraint)constraints.get(i);
                session.doStep(new DeleteConstraint(session, table,
                                                    constraint));
            }
        }
        deleteColumnConstraints(session, table, column.getColumn());
        
        // Remove the column from the table schema
        session.doStep(new DropColumn(session, table, column));

        // Update every row in the table with the new column value
        BCursor bc = null;
        try {
            BlockFile file = db.getFile();
            Expression defaultExpr = column.getDefault();
            Value columnDefault = 
                defaultExpr == null 
                ? ValueNull.valueNull 
                : defaultExpr.getValue(session, null);
            
            IndexConstraint ic = table.getAnyIndex(session);
            Btree index = ic.getIndex(db);
            bc = index.getCursor();
            LazyRow row1 = new LazyRow(table.getColumnCount() + 1);
            Row row2 = new Row(table.getColumnCount());
            final int dc = column.getColumn();
            while (bc.next()) {
                long rowId = bc.getValAsLong();
                db.getRow(rowId, row1, false);
                int del = 0;
                for (int i = 1; i <= row1.size(); i++) {
                    if (i == dc) del++;
                    else row2.set(i - del, row1.item(i));
                }
                UpdateRow update = null;
                if (db.inMemory()) {
                    update = new UpdateRow(session, rowId, row1, row2);
                    row1 = new LazyRow(table.getColumnCount() + 1);
                    row2 = new Row(table.getColumnCount());
                } else {
                    byte[] oldRowBytes = row1.getBytes();
                    byte[] rowBytes = LazyRow.writeRow(session, null, row2);
                    update = new UpdateRow(session, table, rowId,
                                           oldRowBytes, rowBytes);
                }
                session.doStep(update);
            }
        } finally {
            if (bc != null) bc.release();
        }
    }
}