Question

我有这个用于JSF分页的Java代码：

public List<ActiveSessionObj> list(int firstRow, int rowCount, String sortField, boolean sortAscending) throws Exception {

        String SQL_LIST_BY_ORDER_AND_LIMIT = "SELECT * FROM ACTIVESESSIONSLOG ORDER BY ? ? LIMIT ?, ?";



        if (ds == null) {
            throw new SQLException();
        }

        String sortDirection = sortAscending ? "ASC" : "DESC";
        String sql = String.format(SQL_LIST_BY_ORDER_AND_LIMIT, sortField, sortDirection);
        Connection conn = ds.getConnection();
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        List<ActiveSessionObj> dataList = new ArrayList<ActiveSessionObj>();

        try {
            conn.setAutoCommit(false);
            boolean committed = false;
            preparedStatement = conn.prepareStatement(sql);
            preparedStatement.setString(1, sortField);
            preparedStatement.setString(2, sortDirection);
            preparedStatement.setInt(3, firstRow);
            preparedStatement.setInt(4, rowCount);

            resultSet = preparedStatement.executeQuery();
            /* take the result from the SQL query and insert it into Array List collection */
            dataList = ActiveSessionsArrayList(resultSet);

        } catch (SQLException e) {
            throw new Exception(e);
        } finally {
            conn.close();
        }

        return dataList;
    }

我使用此SQL语句生成ArrayList：

SELECT * FROM ACTIVESESSIONSLOG ORDER BY ? ? LIMIT ?, ?

这个SQL查询可以用于Oracle吗？或者这是MySQL特定的？

祝福

Answer 1

LIMIT是MySQL特有的。但是在Oracle中，您可以使用rownum，如下所示：

SELECT *
FROM (SELECT columnA, columnB, rownum as my_rownum
FROM ACTIVESESSIONSLOG
ORDER BY ? ?) 
WHERE my_rownum <= ? 
AND my_rownum >= ?

Answer 2

Case1: If you want first `twenty Records` only then 

 select * from ( 
     select rn,a.*
     from Activesessionlogs a
     order by ??)
 where rn <=20
 order by rn

Case2:If you want the record between `5 to 10` then

select * from (
select rownum rn,e.* from Activesessionlogs e order by ??)
where rn >=5 and rn<=10 
order by rn

<强>例如让我们在下面找一个例子

select * from (
select rownum rn,e.* from emp e order by hiredate)
where rn >=5 and rn<=10
order by rn asc

output

注意：Rownum> or rownum>=无法在同一个查询中使用。一个非常好的博客解释这个Oracle Rownum

Answer 3

不幸的是，LIMIT不是oracle中的有效语句，它在MySql中使用。但是，oracle有一个变量ROWNUM，您可以使用它来限制返回的行数：

select * from mytable where rownum <= 100 and rownum > 50

从您的查询中返回第二个50条记录。

从SQL查询Oracle中检索一系列记录

3 个答案: