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Question

我在尝试对MySql数据库表中的行（记录）求和求和时遇到错误。我要实现的是更新Total_Score表中的term1列。如果任何分数都有变化，那么我必须相应地更新Total_Score列。以下是给出错误的部分编码。

String qry2 = null;
Prepared statement ps2 = null;

qry2 = " UPDATE term1 SET Total_Score = sum(English + Social_Science + Science  + Maths + PE + MAL Arts) WHERE SID = ?";

ps2.=conn.prepareStatement(qry2);
Int res2=ps2.executeUpdate();

Answer 1

该代码中有很多错误：

String qry2 = null;
Prepared statement ps2 = null; // Data type is `PreparedStatement`, not `Prepared statement`

// Don't call `sum()` unless you're summing multiple rows, and you're not.
// What is `MAL Arts`? Column names cannot have spaces, unless you quote
//   the name, and you really don't want to be doing that.
qry2 = " UPDATE term1 SET Total_Score = sum(English + Social_Science + Science  + Maths + PE + MAL Arts) WHERE SID = ?";

ps2.=conn.prepareStatement(qry2); // no period before =
Int res2=ps2.executeUpdate(); // Data type is `int`, not `Int`

似乎您的代码应该是：

String qry2 = "UPDATE term1" +
             " SET Total_Score = English + Social_Science + Science + Maths + PE + MALArts" +
             " WHERE SID = ?";
int res2;
try (PreparedStatement ps2 = conn.prepareStatement(qry2)) {
    ps2.setInt(1, sid);
    res2 = ps2.executeUpdate();
}
// code using `res2` here