Question

我认为这个问题在其他地方没有被问到，但如果您不这么认为，请随时告诉我。

我有两张桌子：

Table A (Transactions)
id ¦ player_id ¦ t_out ¦ team_id

Table B (Players)
id ¦ club_id

我需要做的是计算表A中具有特定表B.club_id的条目数，而表A.t_out为空，表A.team_id是特定值。

注意事项：表A.player_id参见表B.id

我已经浏览了MySql帮助文档，但似乎无法将它拼凑在一起。

Answer 1

这应该适合你：

package com.example.healthcare;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.provider.BaseColumns;


public class StoredValuesDBHelper extends SQLiteOpenHelper {
    // If you change the database schema, you must increment the database version. 
    public static final int DATABASE_VERSION = 1;
    public static final String DATABASE_NAME = "StoredValues.db";
    private static final String TEXT_TYPE = " TEXT";
    private static final String COMMA_SEP = ",";


    public static abstract class ValueEntry implements BaseColumns {
        public static final String TABLE_NAME = "storedvalue";
        public static final String COLUMN_NAME_ENTRY_ID = "entryid";
        public static final String COLUMN_NAME_CONTENT = "content";
    }
    private static final String SQL_CREATE_ENTRIES =
            "CREATE TABLE " + ValueEntry.TABLE_NAME + " (" +
                ValueEntry.COLUMN_NAME_ENTRY_ID + TEXT_TYPE + COMMA_SEP +
                ValueEntry.COLUMN_NAME_CONTENT + TEXT_TYPE + COMMA_SEP +")";
    private static final String SQL_DELETE_ENTRIES =
            "DROP TABLE IF EXISTS " + ValueEntry.TABLE_NAME;

    public StoredValuesDBHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }


    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(SQL_CREATE_ENTRIES);

    }

    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // This database is only a cache for online data, so its upgrade policy is
        // to simply to discard the data and start over
        db.execSQL(SQL_DELETE_ENTRIES);
        onCreate(db);
    }
   public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        onUpgrade(db, oldVersion, newVersion);
    }
}

如何在Mysql中组合多个选择和链接表

1 个答案: