Question

我目前有一个大的SQL语句，我添加以下行以获取每个交易ID的总现金（这是唯一的）：

select sum(cash) from Table a where a.branch = p.branch 
and a.transID = p.transID) TotalCash

我现在需要做同样的事情，但只需要在上个月内有一个有价值的现金值，所以我有这样的事情：

select sum(CASE ValueDate WHEN > @startMonthDate THEN cash ELSE NULL END) 
from Table a where a.branch = p.branch and a.transID = p.transID) TotalMonthCash

很抱歉，我没有完整的声明，但它确实很长，特定于存储过程的上下文，但希望有人知道我的意思？

Answer 1

请改为尝试：

SUM(CASE WHEN ValueDate > @startMonthDate THEN cash ELSE 0 END)

<强>解释

您的CASE表达式语法不正确。您似乎将简单的CASE表达式语法与搜索的CASE表达式语法混淆。请参阅documentation for CASE：

CASE表达式有两种格式：


简单的CASE表达式将表达式与一组简单表达式进行比较，以确定结果。

搜索到的CASE表达式计算一组布尔表达式以确定结果。

您需要搜索的CASE表达式语法：

CASE
     WHEN Boolean_expression THEN result_expression [ ...n ] 
     [ ELSE else_result_expression ] 
END

作为旁注，如果性能是一个问题，如果使用JOIN和GROUP BY而不是使用从属子查询重写，则可能会发现此表达式运行得更快。

Answer 2

尝试移动ValueDate：

select sum(CASE  
             WHEN ValueDate > @startMonthDate THEN cash 
              ELSE 0 
           END) 
 from Table a
where a.branch = p.branch 
  and a.transID = p.transID

（为清晰起见重新格式化）

您可能还会考虑使用'0'而不是NULL，因为您正在进行总和。它可以在两种方式下正常工作，但可能更能说明您的意图。

Answer 3

使用条件“ HAVING”，如果需要，您将使用不超过0的现金清除数据，从而提高效率在您的查询中。

import android.annotation.SuppressLint;
import android.app.Activity;
import android.content.Intent;
import android.content.res.Resources;
import android.net.Uri;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.util.TypedValue;
import android.view.Gravity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.Space;
import android.widget.TextView;
import android.widget.Toast;

public class DrawablesValidator extends Activity {
    public static void ensureDrawablesValid(@NonNull Activity activity) {
        try {
            // IMPORTANT create 1x1 image named pixel.png and put it to all folders
            //           drawable-mdpi
            //           drawable-hdpi
            //           drawable-xhdpi
            //           drawable-xxhdpi
            //           drawable-xxxhdpi
            activity.getDrawable(R.drawable.pixel);
        } catch (Resources.NotFoundException ex) {
            // NOTE optionally, report exception to Crashlytics or just an event to Analytics

            activity.finish();
            activity.startActivity(new Intent(activity, DrawablesValidator.class));
        }
    }

    // NOTE don't care about translations of text messages here, don't put them to strings.xml
    //      we assume, that if user is smart enough to get APK from outside and install it,
    //      then user will definitely understand few messages in English :)
    @SuppressLint("SetTextI18n")
    @Override
    protected void onCreate(Bundle state) {
        super.onCreate(state);

        int dp = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 1, getResources().getDisplayMetrics());
        int dp8 = dp * 8;
        int dp16 = dp * 16;
        int dp80 = dp * 80;

        LinearLayout root = new LinearLayout(this);
        root.setOrientation(LinearLayout.VERTICAL);
        root.setGravity(Gravity.CENTER_HORIZONTAL);
        root.setPadding(dp80, dp16, dp80, dp16);

        Space spaceTop = new Space(this);

        TextView title = new TextView(this);
        title.setPadding(0, dp8, 0, dp8);
        title.setTextSize(20);
        title.setText("Re-install app");

        TextView message = new TextView(this);
        message.setPadding(0, dp8, 0, dp8);
        message.setTextSize(16);
        message.setText("This copy of app is corrupted and can't be launched." +
                "\n\n" +
                "Please, install original version from Google Play");

        Button button = new Button(this);
        button.setPadding(dp16, dp8, dp16, dp8);
        button.setText("Continue");
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try {
                    startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse("https://play.google.com/store/apps/details?id=" + getPackageName())));
                } catch (Exception ex) {
                    Toast.makeText(getApplicationContext(), "Can't open Google Play", Toast.LENGTH_SHORT).show();
                }
            }
        });

        Space spaceBottom = new Space(this);

        int wc = ViewGroup.LayoutParams.WRAP_CONTENT;
        int mp = ViewGroup.LayoutParams.MATCH_PARENT;

        root.addView(spaceTop, lp(0, 0, 1, -1));
        root.addView(title, lp(wc, wc, 0, -1));
        root.addView(message, lp(mp, wc, 0, -1));
        root.addView(button, lp(wc, wc, 0, Gravity.END));
        root.addView(spaceBottom, lp(mp, wc, 1, -1));

        setContentView(root);
    }

    private LinearLayout.LayoutParams lp(int width, int height, int weight, int gravity) {
        LinearLayout.LayoutParams result = new LinearLayout.LayoutParams(width, height);
        result.weight = weight;
        result.gravity = gravity;
        return result;
    }
}

带条件的SQL和

3 个答案: