Java - 从MySQL数据库获取数据 [英] Java - Getting Data from MySQL database
问题描述
我已连接到一个MySQL数据库，其中包含四个字段（第一个是ID，后一个包含varchar字符串）。
I've connected to a MySQL database, which contains four fields (the first of which being an ID, the latter ones each containing varchar strings).
我试图获取数据库的最后一行，并检索字段的内容，以便我可以将它们设置为变量（一个int和三个字符串），并在以后使用。
I am trying to get the last row of the database and retrieve the contents of the fields so that I can set them to variables (an int and three strings) and use them later.
到目前为止，我有最低限度的连接，我从哪里去？正如你可以看到，我试图写一个SQL语句获得最后一行，但它都出了错，从那里，我不知道如何拆分成单独的字段。
So far, I have the bare minimum to make the connection, where do I go from here? As you can see I have tried to write a SQL statement to get the last row but it's all gone wrong from there and I don't know how to split it into the separate fields.
Class.forName("com.mysql.jdbc.Driver").newInstance();
Connection con = DriverManager.getConnection("jdbc:mysql://localhost/t", "", "");
Statement st = con.createStatement();
String sql = ("SELECT * FROM posts ORDER BY id DESC LIMIT 1;");
st.getResultSet().getRow();
con.close();
推荐答案
这里：
Class.forName("com.mysql.jdbc.Driver").newInstance();
Connection con = DriverManager.getConnection("jdbc:mysql://localhost/t", "", "");
Statement st = con.createStatement();
String sql = ("SELECT * FROM posts ORDER BY id DESC LIMIT 1;");
ResultSet rs = st.executeQuery(sql);
if(rs.next()) {
int id = rs.getInt("first_column_name");
String str1 = rs.getString("second_column_name");
}
con.close();
在 rs.getInt 或 rs.getString ，您可以从 1 开始传递 column_id 通过 column_name 作为它更丰富的信息，因为您不必查看数据库表，其中 index 是列。
In rs.getInt or rs.getString you can pass column_id starting from 1, but i prefer to pass column_name as its more informative as you don't have to look at database table for which index is what column.
UPDATE： rs.next
boolean next（）
throws SQLException
boolean next() throws SQLException
将光标从当前位置向下移动一行。 A
ResultSet游标最初位于第一行之前;
首先调用方法next使第一行成为当前行;
第二次调用使第二行成为当前行。
Moves the cursor froward one row from its current position. A ResultSet cursor is initially positioned before the first row; the first call to the method next makes the first row the current row; the second call makes the second row the current row, and so on.
当对下一个方法的调用返回false时，光标位于
后的最后一行。任何调用ResultSet方法（
需要当前行）将导致抛出SQLException。如果
结果集类型是TYPE_FORWARD_ONLY，它是供应商指定的
他们的JDBC驱动程序实现将返回false还是抛出一个
SQLException，然后调用next。
When a call to the next method returns false, the cursor is positioned after the last row. Any invocation of a ResultSet method which requires a current row will result in a SQLException being thrown. If the result set type is TYPE_FORWARD_ONLY, it is vendor specified whether their JDBC driver implementation will return false or throw an SQLException on a subsequent call to next.
如果为当前行打开了输入流，则调用方法
next将隐式关闭它。
If an input stream is open for the current row, a call to the method next will implicitly close it. A ResultSet object's warning chain is cleared when a new row is read.
返回：
如果新的当前行是有效的，则为true; false如果没有更多的行抛出：
SQLException - 如果发生数据库访问错误或在闭合结果集上调用此方法
Returns: true if the new current row is valid; false if there are no more rows Throws: SQLException - if a database access error occurs or this method is called on a closed result set
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