GaussDB中，如何使用SQL将text类型的{"time":93, "n_calls":1, "size":353}转换为json

在GaussDB中，可以使用以下SQL语句将text类型的字符串转换为JSON格式：

SELECT json_build_object('time', (json_data->>'time')::INT, 'n_calls', (json_data->>'n_calls')::INT, 'size', (json_data->>'size')::INT)
FROM your_table;

其中，`json_data`是保存这个text类型字符串的列名，`your_table`是表名。

相关问题

std::condition_variable

std::condition_variable is a synchronization primitive provided by the C++ Standard Library that enables threads to wait for a certain condition to become true. It is typically used in conjunction with a std::mutex to protect access to shared data.

The basic idea is that one or more threads wait on the condition variable until some other thread signals it. The waiting threads are blocked until the condition variable is notified, at which point one or more of them are unblocked and can proceed.

To use std::condition_variable, you typically follow these steps:

1. Define a std::condition_variable object.
2. Define a std::mutex object to protect access to shared data.
3. Define a boolean variable that represents the condition that the threads are waiting for.
4. Use the mutex to protect access to the shared data and the condition variable.
5. When a thread needs to wait for the condition to become true, it calls wait() on the condition variable while holding the mutex.
6. When the condition becomes true, some other thread calls notify_one() or notify_all() on the condition variable to wake up the waiting thread(s).

Here's some example code:

#include <mutex>
#include <condition_variable>
#include <thread>
#include <iostream>

std::mutex mtx;
std::condition_variable cv;
bool ready = false;

void worker()
{
    std::unique_lock<std::mutex> lock(mtx);
    while (!ready) {
        cv.wait(lock);
    }
    std::cout << "Worker thread got signal!\n";
}

int main()
{
    std::thread t(worker);

    // Do some work here...

    {
        std::lock_guard<std::mutex> lock(mtx);
        ready = true;
    }
    cv.notify_one();

    t.join();
    return 0;
}

In this example, the main thread starts a worker thread and does some work. When the work is done, it signals the worker thread by setting the "ready" flag to true and calling notify_one() on the condition variable. The worker thread is blocked on the condition variable until it receives the signal, at which point it prints out a message.

java.lang.SecurityException: Neither user 10229 nor current process has android.permission.ANSWER_PHONE_CALLS.

这个异常表示当前应用程序没有 `android.permission.ANSWER_PHONE_CALLS` 权限。在 Android 8.0 及以上的版本中，只有拥有该权限的应用程序才能接听和拒绝来电。

要解决这个问题，可以在 AndroidManifest.xml 文件中添加以下权限：

<uses-permission android:name="android.permission.ANSWER_PHONE_CALLS" />

同时，在应用程序中还需要动态请求该权限。可以使用以下代码请求该权限：

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
    if (ContextCompat.checkSelfPermission(this, Manifest.permission.ANSWER_PHONE_CALLS) !=
            PackageManager.PERMISSION_GRANTED) {
        ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.ANSWER_PHONE_CALLS}, REQUEST_CODE_ANSWER_PHONE_CALLS);
    }
}

其中，`REQUEST_CODE_ANSWER_PHONE_CALLS` 是一个自定义的请求码，用于在权限请求结果返回时进行判断。需要注意的是，应用程序需要在运行时请求该权限，并且用户需要在权限请求对话框中授权才能接听和拒绝来电。