Java 如何使用union运算符连接sql查询

试试这个：

String Query="select * from recommendation.sports WHERE feed LIKE'%"+s1+"%'

    UNION "select * from recommendation.software  WHERE feed LIKE '%"+s1+"%'

    UNION "select * from recommendation.website   WHERE feed LIKE '%"+s1+"%'

    UNION "select * from recommendation.others    WHERE feed LIKE '%"+s1+"%'

    UNION "select * from recommendation.business  WHERE feed LIKE '%"+s1+"%'";

也许你是说这个

 String Query="select * from recommendation.sports WHERE feed LIKE'%"+s1+"%'

    UNION select * from recommendation.software  WHERE feed LIKE '%"+s1+"%'

    UNION select * from recommendation.website   WHERE feed LIKE '%"+s1+"%'

    UNION select * from recommendation.others    WHERE feed LIKE '%"+s1+"%'

    UNION select * from recommendation.business  WHERE feed LIKE '%"+s1+"%'";

但是我建议您在查询中使用

PreparedStatements

，以避免

SQL注入

String Query = "select * from recommendation.sports WHERE feed LIKE '%" + s1 + "%' " +
                "UNION " +
                "select * from recommendation.software  WHERE feed LIKE '%" +s1+ "%' " +
                "UNION " +
                "select * from recommendation.website   WHERE feed LIKE '%" +s1+" %' " +
                "UNION " +
                "select * from recommendation.others    WHERE feed LIKE '%"+s1+"%' " +
                "UNION " +
                "select * from recommendation.business  WHERE feed LIKE '%" +s1+ "%'" ;

---

有些小改动，请查看

String Query = "select * from recommendation.sports WHERE feed LIKE CONCAT('%', ?, '%') " +
                "UNION " +
                "select * from recommendation.software  WHERE feed LIKE CONCAT('%', ?, '%') " +
                "UNION " +
                "select * from recommendation.website   WHERE feed LIKE CONCAT('%', ?, '%') " +
                "UNION " +
                "select * from recommendation.others    WHERE feed LIKE CONCAT('%', ?, '%')  " +
                "UNION " +
                "select * from recommendation.business  WHERE feed LIKE CONCAT('%', ?, '%')" ;

PreparedStatement pstmt = con.prepareStatement(Query);
pstmt.setString(1, s1);
pstmt.setString(2, s1);
pstmt.setString(3, s1);
pstmt.setString(4, s1);
pstmt.setString(5, s1);
ResultSet _result = pstmt.executeQuery();

---

试试这个，告诉我它是否有效。
检查..上面的代码在mysql数据库中运行良好，与jdbc中使用的代码相同，我在标记“UNION”上得到编译时错误语法错误，[expected@R.J上述代码在mysql数据库中运行良好，与jdbc i中使用的代码相同，在标记“UNION”上出现编译时错误语法错误，[预计我会尝试修改代码，但它不起作用，如果所有表都没有确切的列名、类型和顺序，您可以使用select*修改我的代码吗？如果所有表都没有确切的列名、类型和顺序，您的代码将不起作用。您在每个

UNION

和

select

之间有一个额外的双引号，很抱歉，您的代码也会出错，您的代码在mysql数据库中工作正常，但在jdbc，它得到了一个error@JVV您的代码在mysql数据库中运行良好，但在jdbc中，如果您使用prepared语句重新编写代码，则会出现错误。@jvv String literal未正确地用双精度-quote@JVV字符串文字未被双引号正确关闭

String Query="select * from recommendation.sports WHERE feed LIKE \'%"+s1+"%\'

    UNION select * from recommendation.software  WHERE feed LIKE \'%"+s1+"%\'

    UNION select * from recommendation.website   WHERE feed LIKE \'%"+s1+"%\'

    UNION select * from recommendation.others    WHERE feed LIKE \'%"+s1+"%\'

    UNION select * from recommendation.business  WHERE feed LIKE \'%"+s1+"%\'";