Question

我有一个Postgresql数据库，我想使用JDBC截断一些表。我该怎么做？

这是我尝试过的，但没有一个工作......甚至没有报告任何错误：

使用CallableStatement。

try (Connection connection = getConnection();
     CallableStatement statement = connection.prepareCall("TRUNCATE " + tableName)) {
  return statement.execute();
}

使用Statement。

try (Connection connection = getConnection();
     Statement statement  = connection.createStatement()) {
  return statement.execute("TRUNCATE " + tableName);
}

使用PreparedStatement。

try (Connection connection = getConnection();
     PreparedStatement statement = connection.prepareStatement("TRUNCATE " + tableName)) {
  return statement.execute();
}

Answer 1

截断后，我需要提交：

try (Connection connection = getConnection();
     Statement statement = connection.createStatement()) {
  int result = statement.executeUpdate("TRUNCATE " + tableName);
  connection.commit();
  return result;
}

来自the documentation：

TRUNCATE对于表中的数据是事务安全的：如果周围的事务没有提交，截断将被安全地回滚。

Answer 2

如果表具有依赖关系，则可能会遇到问题。如果是这样，首先截断父表，并使用CASCADE选项。

Connection connection = getConnection();
try {
    PreparedStatement statement  = connection.prepareStatement("TRUNCATE " + parentTable1, parentTable2, ... + " CASCADE");
    try {
        return statement.execute();
    } finally {
        statement.close();
    }
} finally {
    connection.close();
}

Answer 3

首先，如果要截断一个表，您可能还希望重新启动身份（除了可能进行CASCADE之外，如John Hogan所述）。

第二，就进行connection.commit（）而言，假设您已将自动提交设置为OFF。我的Postgres设置为ON（显然，这有时是默认设置）。如果将其设置为ON，则不需要调用提交，这将导致错误： “ org.postgresql.util.PSQLException：启用autoCommit后无法提交。”

第三，您可能无权截断表（或重新启动标识）。在这种情况下，您将需要：

DELETE from your_table
SELECT setval('your_table_id', 1)

以下对我有用：

public String truncateTable(String tableName, boolean cascadeFlag) {
    String message = "";
    try {
        connection = DriverManager.getConnection(url, username, password);
        Statement statement = connection.createStatement();
        String truncation = "TRUNCATE TABLE yourSchema." + tableName + " RESTART IDENTITY" + (cascadeFlag ? " CASCADE" : "");
        System.out.println("truncateTable: Executing query '" + truncation + "'.");
        int result = statement.executeUpdate(truncation);
        // connection.commit();  // If autocommit is enabled (which it is for our DB), then throws exception after truncating the table.
        statement.close();
        connection.close();
    } catch (SQLException sqlex) {
        message = "Could not truncate table " + tableName + ". " + sqlex.getMessage();
        System.err.println(message);
        sqlex.printStackTrace();
    }
    return message;
}

也：

public int deleteResetTable(String tableName, String fieldName) {
        int affectedRows = 0;
        try {
            connection = DriverManager.getConnection(url, username, password);
            String sql = "DELETE FROM yourSchema." + tableName;
            PreparedStatement preparedStatement = connection.prepareStatement(sql);
            affectedRows = preparedStatement.executeUpdate();
            System.out.println("Deleted " + affectedRows+ " rows from table " + tableName + ".");
            sql = "SELECT setval('yourSchema." + fieldName + "', 1)";
            preparedStatement = connection.prepareStatement(sql);
            affectedRows = preparedStatement.executeUpdate();
            System.out.println("Reset " + affectedRows+ " values from table " + tableName + ".");
        } catch (SQLException ex) {
            System.out.println("Failed to delete rows from " + tableName + " " + ex.getMessage());
        }
        return affectedRows;
}

如何从JDBC截断Postgresql的表

3 个答案: