sqlserver2005 分页优化

有同学强调我对sql server的分页不了解，在mssql 2000之前只能通过top进行分页。我没有说top分页不对，我是说在hibernate的sql server方言里面，针对sql server 的top分页是不对的。至少在我使用的版本里是不对的。而且有很多同学也遇到和我类似的问题。请大家打开hibernate的showsql，看看生成的sql 语句再来判断正确还是错误，谢谢！
提到Hibernate，好多人都用“垃圾”，“效率太低”这样的字眼评价。其实任何一个框架的产生都是有原因的，这些为企业级开发产生的框架最初只是为了简化开发，或许会有一些影响性能的地方。但是通过配置和巧妙的办法，完全可以规避这些问题，发挥最大的效果。至少目前我的项目，日均pv在500w左右目前还没发现什么问题。
一、hibernate分页 hibernate对MsSql的伪分页
分页是web项目中比不可少的一个功能，数据量大的时候不能全部展示必然要用到分页技术。相信大家对hibernate中的分页都不陌生：

public Query setMaxResults(int maxResults);
 public Query setFirstResult(int firstResult);

public Query setMaxResults(int maxResults);
public Query setFirstResult(int firstResult);

只要调用了这两个方法并设置好参数，hibernate自动分页完全屏蔽了底层数据库分页技术，这也是众多开发者喜欢hibernate的原因之一。
项目开发中遇到一个奇怪的问题。数据库采用的是Sql Server 2005，也设置了上面两个参数，可是每次发送到数据库端的SQL语句都是select top ....语句。即便是查询第10w条，也只有一个select top 语句，不免引起对hibernate实现sql server分页的怀疑。hibernate针对不同数据库实现的分页方法封装在对应数据库的方言里，通过getLimitString方法转化成对应数据库的分页算法。
以常见的Mysql数据库的方言MySQLDialect为例：

public String getLimitString(String sql, boolean hasOffset) {
         return new StringBuffer( sql.length() + 20 )
                .append( sql )
                 .append( hasOffset ? " limit ?, ?" : " limit ?" )
                .toString();
    }

public String getLimitString(String sql, boolean hasOffset) {
		return new StringBuffer( sql.length() + 20 )
				.append( sql )
				.append( hasOffset ? " limit ?, ?" : " limit ?" )
				.toString();
	}

采用了大家熟悉的mysql的limit进行分页。
Oracle数据库的方言Oracle9iDialect：

StringBuffer pagingSelect = new StringBuffer( sql.length()+100 );
         if (hasOffset) {
             pagingSelect.append("select * from ( select row_.*, rownum rownum_ from ( ");
        }
         else {
             pagingSelect.append("select * from ( ");
        }
        pagingSelect.append(sql);
         if (hasOffset) {
             pagingSelect.append(" ) row_ where rownum <= ?) where rownum_ > ?");
        }
         else {
             pagingSelect.append(" ) where rownum <= ?");
        }

StringBuffer pagingSelect = new StringBuffer( sql.length()+100 );
		if (hasOffset) {
			pagingSelect.append("select * from ( select row_.*, rownum rownum_ from ( ");
		}
		else {
			pagingSelect.append("select * from ( ");
		}
		pagingSelect.append(sql);
		if (hasOffset) {
			pagingSelect.append(" ) row_ where rownum <= ?) where rownum_ > ?");
		}
		else {
			pagingSelect.append(" ) where rownum <= ?");
		}

利用Oracle的rownum 结合三层嵌套查询完成分页。这个三层是Oracle最经典高效的分页算法。
可是针对Sql Server的方言SQLServerDialect：

public String getLimitString(String querySelect, int offset, int limit) {
         if ( offset > 0 ) {
             throw new UnsupportedOperationException( "query result offset is not supported" );
        }
         return new StringBuffer( querySelect.length() + 8 )
                .append( querySelect )
                 .insert( getAfterSelectInsertPoint( querySelect ), " top " + limit )
                .toString();
    }

public String getLimitString(String querySelect, int offset, int limit) {
		if ( offset > 0 ) {
			throw new UnsupportedOperationException( "query result offset is not supported" );
		}
		return new StringBuffer( querySelect.length() + 8 )
				.append( querySelect )
				.insert( getAfterSelectInsertPoint( querySelect ), " top " + limit )
				.toString();
	}

揉揉眼睛、再揉揉，没错，只出现了一个top语句。这就意味着如果查询第10w页的数据，需要把前10w页数据全部提取出来。hibernate针对sql server的分页是伪分页，所以随着数据量日益增加用户抱怨系统速度慢，程序员抱怨hibernate性能低，dba抱怨开发人员sql功底太浅。
不知道hibernate开发组，出于什么目前或情况没有真正提供sql server的分页技术，那我们自己来实现。
方言类：

public class SQLServer2005Dialect extends SQLServerDialect {

     /**
     *
     * 是否需要绑定limit参数?
     *
     * 在SQL Server中使用top时不能使用参数表示top条数,而使用ROW_NUMBER()则需要提供limit参数
     */

     private ThreadLocal<Boolean> supportsVariableLimit = new ThreadLocal<Boolean>();
     public SQLServer2005Dialect() {
         registerFunction("bitand", new BitAndFunction());
         registerFunction("bitxor", new BitXorFunction());
         registerFunction("bitor", new BitOrFunction());
         setSupportsVariableLimit(false);
    }

     /**
     *
     * <p>
     * 设置是否先绑定limit参数。
     * </p>
     *
     * @param first
     */

     private void setSupportsVariableLimit(boolean first) {
         this.supportsVariableLimit.set(Boolean.valueOf(first));
    }

     /**
     *
     * <p>
     * 获取sql中select子句位置。
     * </p>
     *
     * @param sql
     *
     * @return int
     */
     protected static int getSqlAfterSelectInsertPoint(String sql) {
         int selectIndex = sql.toLowerCase().indexOf("select");

         int selectDistinctIndex = sql.toLowerCase().indexOf("select distinct");

         return selectIndex + ((selectDistinctIndex == selectIndex) ? 15 : 6);
    }

     public boolean supportsLimitOffset() {
         return true;
    }

     /*
     * Hibernate在获得Limit String(已添加了limit子句)后，如果此方法返回true，
     *
     * 则会添加额外的参数值(ROW_NUMBER()范围)(策略可能是这样：有offset设置两个参数值，没有设置一个参数值)
     */
     public boolean supportsVariableLimit() {
         return ((Boolean) this.supportsVariableLimit.get()).booleanValue();
    }

     public boolean useMaxForLimit() {
         return true;
    }
     /**
     * 首页top，以后用ROW_NUMBER
     */
     public String getLimitString(String query, int offset, int limit) {
         setSupportsVariableLimit(offset > 0);

         if (offset == 0) {
             return new StringBuffer(query.length() + 8).append(query).insert(
                     getSqlAfterSelectInsertPoint(query), " top " + limit)
                    .toString();
        }

         return getLimitString(query, offset > 0);
    }

     public String getLimitString(String sql, boolean hasOffset) {
         int orderByIndex = sql.toLowerCase().lastIndexOf("order by");

         if (orderByIndex <= 0) {
             throw new UnsupportedOperationException(
                     "must specify 'order by' statement to support limit operation with offset in sql server 2005");
        }

         String sqlOrderBy = sql.substring(orderByIndex + 8);

         String sqlRemoveOrderBy = sql.substring(0, orderByIndex);

         int insertPoint = getSqlAfterSelectInsertPoint(sql);
         return new StringBuffer(sql.length() + 100)
                 .append("with tempPagination as(")
                .append(sqlRemoveOrderBy)
                .insert(
                         insertPoint + 23,
                         " ROW_NUMBER() OVER(ORDER BY " + sqlOrderBy
                                 + ") as RowNumber,")
                .append(
                         ") select * from tempPagination where RowNumber>?  and RowNumber<=?")
                .toString();
    }
}

public class SQLServer2005Dialect extends SQLServerDialect {

	/**
	 * 
	 * 是否需要绑定limit参数?
	 * 
	 * 在SQL Server中使用top时不能使用参数表示top条数,而使用ROW_NUMBER()则需要提供limit参数
	 */

	private ThreadLocal<Boolean> supportsVariableLimit = new ThreadLocal<Boolean>();
	public SQLServer2005Dialect() {
		registerFunction("bitand", new BitAndFunction());
		registerFunction("bitxor", new BitXorFunction());
		registerFunction("bitor", new BitOrFunction());
		setSupportsVariableLimit(false);
	}

	/**
	 * 
	 * <p>
	 * 设置是否先绑定limit参数。
	 * </p>
	 * 
	 * @param first
	 */

	private void setSupportsVariableLimit(boolean first) {
		this.supportsVariableLimit.set(Boolean.valueOf(first));
	}

	/**
	 * 
	 * <p>
	 * 获取sql中select子句位置。
	 * </p>
	 * 
	 * @param sql
	 * 
	 * @return int
	 */
	protected static int getSqlAfterSelectInsertPoint(String sql) {
		int selectIndex = sql.toLowerCase().indexOf("select");

		int selectDistinctIndex = sql.toLowerCase().indexOf("select distinct");

		return selectIndex + ((selectDistinctIndex == selectIndex) ? 15 : 6);
	}

	public boolean supportsLimitOffset() {
		return true;
	}

	/*
	 * Hibernate在获得Limit String(已添加了limit子句)后，如果此方法返回true，
	 * 
	 * 则会添加额外的参数值(ROW_NUMBER()范围)(策略可能是这样：有offset设置两个参数值，没有设置一个参数值)
	 */
	public boolean supportsVariableLimit() {
		return ((Boolean) this.supportsVariableLimit.get()).booleanValue();
	}

	public boolean useMaxForLimit() {
		return true;
	}
	/**
	 * 首页top，以后用ROW_NUMBER
	 */
	public String getLimitString(String query, int offset, int limit) {
		setSupportsVariableLimit(offset > 0);

		if (offset == 0) {
			return new StringBuffer(query.length() + 8).append(query).insert(
					getSqlAfterSelectInsertPoint(query), " top " + limit)
					.toString();
		}

		return getLimitString(query, offset > 0);
	}
	
	public String getLimitString(String sql, boolean hasOffset) {
		int orderByIndex = sql.toLowerCase().lastIndexOf("order by");

		if (orderByIndex <= 0) {
			throw new UnsupportedOperationException(
					"must specify 'order by' statement to support limit operation with offset in sql server 2005");
		}

		String sqlOrderBy = sql.substring(orderByIndex + 8);

		String sqlRemoveOrderBy = sql.substring(0, orderByIndex);

		int insertPoint = getSqlAfterSelectInsertPoint(sql);
		return new StringBuffer(sql.length() + 100)
				.append("with tempPagination as(")
				.append(sqlRemoveOrderBy)
				.insert(
						insertPoint + 23,
						" ROW_NUMBER() OVER(ORDER BY " + sqlOrderBy
								+ ") as RowNumber,")
				.append(
						") select * from tempPagination where RowNumber>?  and RowNumber<=?")
				.toString();
	}
}

函数：

public class BitAndFunction implements SQLFunction {
     public Type getReturnType(Type type, Mapping mapping) {
         return Hibernate.INTEGER;
    }

     public boolean hasArguments() {
         return true;
    }

     public boolean hasParenthesesIfNoArguments() {
         return true;
    }

     public String render(List args, SessionFactoryImplementor factory)
             throws QueryException {
         if (args.size() != 2) {
             throw new IllegalArgumentException(
                     "BitAndFunction requires 2 arguments!");
        }
         return args.get(0).toString() + " & " + args.get(1).toString();
    }
}

public class BitAndFunction implements SQLFunction {
	public Type getReturnType(Type type, Mapping mapping) {
		return Hibernate.INTEGER;
	}

	public boolean hasArguments() {
		return true;
	}

	public boolean hasParenthesesIfNoArguments() {
		return true;
	}

	public String render(List args, SessionFactoryImplementor factory)
			throws QueryException {
		if (args.size() != 2) {
			throw new IllegalArgumentException(
					"BitAndFunction requires 2 arguments!");
		}
		return args.get(0).toString() + " & " + args.get(1).toString();
	}
}

 

public class BitOrFunction implements SQLFunction {
     public Type getReturnType(Type type, Mapping mapping) {
         return Hibernate.INTEGER;
    }
     public boolean hasArguments() {
         return true;
    }
     public boolean hasParenthesesIfNoArguments() {
         return true;
    }
     public String render(List args, SessionFactoryImplementor factory)
             throws QueryException {
         if (args.size() != 2) {
             throw new IllegalArgumentException(
                     "BitOrFunction requires 2 arguments!");
        }
         return args.get(0).toString() + " | " + args.get(1).toString();
    }
}

public class BitOrFunction implements SQLFunction {
	public Type getReturnType(Type type, Mapping mapping) {
		return Hibernate.INTEGER;
	}
	public boolean hasArguments() {
		return true;
	}
	public boolean hasParenthesesIfNoArguments() {
		return true;
	}
	public String render(List args, SessionFactoryImplementor factory)
			throws QueryException {
		if (args.size() != 2) {
			throw new IllegalArgumentException(
					"BitOrFunction requires 2 arguments!");
		}
		return args.get(0).toString() + " | " + args.get(1).toString();
	}
}

 

Java代码  

public Type getReturnType(Type type, Mapping mapping) {
         return Hibernate.INTEGER;
    }
     public boolean hasArguments() {
         return true;
    }
     public boolean hasParenthesesIfNoArguments() {
         return true;
    }
     public String render(List args, SessionFactoryImplementor factory)
             throws QueryException {
         if (args.size() != 2) {
             throw new IllegalArgumentException(
                     "BitXorFunction requires 2 arguments!");
        }
         return args.get(0).toString() + " ^ " + args.get(1).toString();
    }

转载：http://www.iteye.com/topic/721903