如何选择MySQL表的最后一行？ 我没有任何自动增量键

Question

I want to SELECT the last row in a MySQL table. I don't have any auto increment key in that table.

public String getLastLeaveId() {
    try {
        Statement stmt  = getConnection();
        String sql="select leaveID from applied leave"; // here I want some logic that will fetch only leave_id from last row only
        stmt.execute(sql);
    } catch (SQLException e) {
        e.printStackTrace();
    }
    return null;
}

//Table Structure --->
(leave_id varchar(50) primary key,emp_id varchar(40),birthday varchar(20),anniv varchar(20),rh varchar(200),total int,foriegn key(emp_id) reference employee);

Answer 1

降序排列在您现在要订购的任何列上，最后limit 0,1 。

Answer 2

There is no implicit ordering in a database table. If you don't have an auto-increment column, a date/time column, or some other column that follows a natural order when you insert rows, you're limited to using some other way of faking it.

You don't show a table structure in your question, nor do you state whether you're using MyISAM or InnoDB. MyISAM stores rows in order they're inserted (usually) so you can use something inneficient like ResultSet.last() from Java to get the last row, but if you're not using MyISAM you can't depend on that. InnoDB, the default storage engine, stores records in a more efficient B-Tree order, and does not retain the insert order at all, but rather stores records according to the primary key's order.

In short, you'll need to pick a field that has some natural order (or invent one) and order by that.

Answer 3

it's may be useful

   SELECT MAX(ID) FROM YourTable

   // Similarly, ORDER BY with LIMIT:

    SELECT ID FROM YourTable ORDER BY ID Desc Limit 1

Answer 4

Without having either a where clause and/or order by condition you can't fetch the last row in a query directly. You need to traverse through all the rows to stop before last row.

Only positive options I see are:

1. Select all rows. execute a rs.last() and then read it.
2. Use order by desc clause based on a column.
3. Define a virtual row_num on all selected rows and run a select with desc order on that row_num.
4. Execute two statements. One to find row count and the second to limit to fetch last row.

Pseudo example on 4th option above:

• int rowCount = result from "Select count(*) from my_table";
• String query = "select * from my_table limit " + ( rowCount - 1 ) + ", 1";
• rs = stmt.execute above query.
• read the only record, none but the last record, from rs, fetched.

Answer 5

这就是你想要的。

SELECT * FROM table_name ORDER BY id DESC LIMIT 1