如何从两个不同的表中获取数据（没有重复记录）？(How to fetch data ( without duplicates records ) from two different tables ? where both tables have common value)

 解释究竟是什么让你错误的方法失败是次要的：主要的是修复方法。 
 
 对于此通信模式，您应该使用所有HTTP作业发送其状态的actor ，而不是async-await或launch 。 这将自动处理所有并发问题。 
 
 以下是一些示例代码，取自您在评论中提供的链接，并根据您的用例进行了调整。 而不是某些第三方要求它获取计数器值并使用它更新GUI，actor在UI上下文中运行并更新GUI本身： 
 
import kotlinx.coroutines.experimental.*
import kotlinx.coroutines.experimental.channels.*
import kotlin.system.*
import kotlin.coroutines.experimental.*

object IncCounter

fun counterActor() = actor<IncCounter>(UI) {
    var counter = 0
    for (msg in channel) {
        updateView(++counter)
    }
}

fun main(args: Array<String>) = runBlocking {
    val counter = counterActor()
    massiveRun(CommonPool) {
        counter.send(IncCounter)
    }
    counter.close()
    println("View state: $viewState")
}


// Everything below is mock code that supports the example
// code above:

val UI = newSingleThreadContext("UI")

fun updateView(newVal: Int) {
    viewState = newVal
}

var viewState = 0

suspend fun massiveRun(context: CoroutineContext, action: suspend () -> Unit) {
    val numCoroutines = 1000
    val repeatActionCount = 1000
    val time = measureTimeMillis {
        val jobs = List(numCoroutines) {
            launch(context) {
                repeat(repeatActionCount) { action() }
            }
        }
        jobs.forEach { it.join() }
    }
    println("Completed ${numCoroutines * repeatActionCount} actions in $time ms")
}
 
 运行它打印 
 
Completed 1000000 actions in 2189 ms
View state: 1000000

The explanation what exactly makes your wrong approach fail is secondary: the primary thing is fixing the approach.
 
Instead of async-await or launch, for this communication pattern you should instead have an actor to which all the HTTP jobs send their status. This will automatically handle all your concurrency issues.
 
Here's some sample code, taken from the link you provided in the comment and adapted to your use case. Instead of some third party asking it for the counter value and updating the GUI with it, the actor runs in the UI context and updates the GUI itself:
 
import kotlinx.coroutines.experimental.*
import kotlinx.coroutines.experimental.channels.*
import kotlin.system.*
import kotlin.coroutines.experimental.*

object IncCounter

fun counterActor() = actor<IncCounter>(UI) {
    var counter = 0
    for (msg in channel) {
        updateView(++counter)
    }
}

fun main(args: Array<String>) = runBlocking {
    val counter = counterActor()
    massiveRun(CommonPool) {
        counter.send(IncCounter)
    }
    counter.close()
    println("View state: $viewState")
}


// Everything below is mock code that supports the example
// code above:

val UI = newSingleThreadContext("UI")

fun updateView(newVal: Int) {
    viewState = newVal
}

var viewState = 0

suspend fun massiveRun(context: CoroutineContext, action: suspend () -> Unit) {
    val numCoroutines = 1000
    val repeatActionCount = 1000
    val time = measureTimeMillis {
        val jobs = List(numCoroutines) {
            launch(context) {
                repeat(repeatActionCount) { action() }
            }
        }
        jobs.forEach { it.join() }
    }
    println("Completed ${numCoroutines * repeatActionCount} actions in $time ms")
}
 
Running it prints
 
Completed 1000000 actions in 2189 ms
View state: 1000000