java - 如何在 JDBC 中使用 MySQL 子查询？

Question

示例查询:

SELECT country 
FROM data 
WHERE city LIKE 
(SELECT LEFT ('jakartada',7));

JDBC 中的示例:

String sql = " SELECT country FROM data WHERE city LIKE (SELECT LEFT ('?',7)) ";
PreparedStatement ps = koneksi.prepareStatement(sql);
ps.setString(1,     city    );
ResultSet rs = ps.executeQuery();

为什么这不能正常工作？

Answer 1

准备好的语句中没有参数，但是代码尝试设置参数。尝试向语句中添加一个参数。

String sql = " SELECT country FROM data WHERE city LIKE (SELECT LEFT (?,7)) ";
PreparedStatement ps = koneksi.prepareStatement(sql);
ps.setString(1,     city    );
ResultSet rs = ps.executeQuery();

或者尝试删除设置参数的语句:

String sql = " SELECT country FROM data WHERE city LIKE (SELECT LEFT ('jakartada',7)) ";
PreparedStatement ps = koneksi.prepareStatement(sql);
ResultSet rs = ps.executeQuery();