如何为 PreparedStatements 重写 SQL 语句？

Question

我想将下面的 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，相似：

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

Answer 1

你会做：

SELECT ?, ?

然后使用生成的 PreparedStatement 对象，您将绑定参数：

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

当您执行循环或使用通过方法传递给您的变量时，这比您在代码中已经知道的常量（以防出现这种情况）更有优势

Answer 2

您必须在两个语句中执行此操作：

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();

编辑我忘记了 Postgres 允许在一个 PreparedStatement:

中包含多个 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是你只指定值一次是这样的：

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();

如何为 PreparedStatements 重写 SQL 语句？

How to rewrite SQL statements for PreparedStatements?

java

sql

postgresql

jdbc