Question

我想将folling SQL语句重写为动态PreparedStatement java：

UPDATE table SET field='C' WHERE id=3;
INSERT INTO table (id, field)
       SELECT 3, 'C'
       WHERE NOT EXISTS (SELECT 1 FROM table WHERE id=3);

特别是我不知道如何将SELECT 3, 'C'行重写为动态语句。

UPDATE table SET name=:name WHERE id=:id
INSERT INTO table (id, name)
       SELECT 3, 'C'  <-- how could I rewrite these values to take the dynamic values from PreparedStatement?
       WHERE NOT EXISTS (SELECT 1 FROM table WHERE id=3);

我的对象，类似：

@Entity
public class MyEntity {
   long id, String name;
}

Answer 1

你必须在两个陈述中这样做：

PreparedStatement update = connection.prepareStatement(
    "UPDATE table SET field=? WHERE id=?");

PreparedSTatement insert = connection.prepareStatement(
    "INSERT INTO table (id, field) \n" +
    "       SELECT ?, ? \n" +
    "       WHERE NOT EXISTS (SELECT 1 FROM table WHERE id=?)";

update.setString(1, "C");
update.setInt(2, 3);
update.executeUpdate();

insert.setInt(1, 3);
insert.setString(2, "C");
insert.setInt(3, 3);
insert.executeUpdate();

connection.commit();

编辑我忘了Postgres在一个PreparedStatement中允许多个SQL语句：

PreparedStatement stmt = connection.prepareStatement(
    "UPDATE table SET field=? WHERE id=?;\n" + 
    "INSERT INTO table (id, field) \n" +
    "       SELECT ?, ? \n" +
    "       WHERE NOT EXISTS (SELECT 1 FROM table WHERE id=?)";

stmt.setString(1, "C");
stmt.setInt(2, 3);
stmt.setInt(3, 3);
stmt.setString(4, "C");
stmt.setInt(5, 3);
stmt.executeUpdate();

connection.commit();

Edit2 我能想到的唯一方法就是一次指定值：

String sql = "with data (id, col1) as ( \n" + " values (?, ?) \n" + "), updated as ( \n" + " \n" + " UPDATE foo \n" + " SET field = (select col1 from data) \n" + " WHERE id = (select id from data) \n" + ") \n" + "insert into foo \n" + "select id, col1 \n" + "from data \n" + "where not exists (select 1 \n" + " from foo \n" + " where id = (select id from data))"; pstmt = connection.prepareStatement(sql); pstmt.setInt(1, 3); pstmt.setString(2, "C"); pstmt.executeUpdate();

Answer 2

你会这样做：

SELECT ?, ?

然后使用生成的PreparedStatement对象，绑定参数：

myPreparedStatement.setLong(1, 3); //The first ? found
myPreparedStatement.setString(2, "C");

当您进行循环或使用通过方法传递给您的变量时，这更有利，而不是您已经在代码中知道的常量（如果出现的话）

如何为PreparedStatements重写SQL语句？

2 个答案: