在 SQLite 中生成平均值
Posted
技术标签:
【中文标题】在 SQLite 中生成平均值【英文标题】：Generate an Average in SQLite 【发布时间】：2018-12-23 05:31:49 【问题描述】：在我的应用程序中，我有 4 个活动，每个活动都与我的 SQLite 数据库中的一个表相关联。
-
联赛 = 联赛
保龄球桌 = 保龄球桌
系列 = 系列表
游戏 = 游戏桌
我正在尝试找出为每个系列生成平均分数的最佳方法。在将新游戏添加到系列之前，不会生成游戏 ID。
当投球手输入他/她的分数时，id 可能看起来像这样；
联赛 ID = 1 投球手 id = 3 系列 ID = 6 游戏 ID = 9,10,11为系列 id 6 生成平均值的最佳解决方案是什么。我认为应该在每次输入分数并将其写入系列表中的平均值字段时生成平均值。有什么想法吗？
列出投球手比赛的方法：
public List<Game> getAllGames(String leagueId, String bowlerId, String seriesId)
List<Game> games = new ArrayList<>();
//Select All Query
String selectQuery = "SELECT * FROM " + Game.TABLE_NAME + " WHERE " + Game.COLUMN_LEAGUE_ID + " = '" + leagueId + "'" + " AND " + Game.COLUMN_BOWLER_ID + " = '" + bowlerId + "'" + " AND " + Game.COLUMN_SERIES_ID + " = '" + seriesId + "'" + " ORDER BY " +
Game.COLUMN_TIMESTAMP + " DESC";
try (SQLiteDatabase db = this.getWritableDatabase())
@SuppressLint("Recycle") Cursor cursor = db.rawQuery( selectQuery, null );
//Looping Through All Rows And Adding To The List
if (cursor.moveToFirst())
do
Game game1 = new Game();
game1.setId(cursor.getInt(cursor.getColumnIndex(Game.COLUMN_ID ) ) );
game1.setLeagueId(cursor.getString(cursor.getColumnIndex(Game.COLUMN_LEAGUE_ID)));
game1.setBowlerId(cursor.getString(cursor.getColumnIndex(Game.COLUMN_BOWLER_ID)));
game1.setSeriesId(cursor.getString(cursor.getColumnIndex(Game.COLUMN_SERIES_ID)));
game1.setScore(cursor.getString(cursor.getColumnIndex(Game.COLUMN_SCORE)));
game1.setStrikes(cursor.getString(cursor.getColumnIndex(Game.COLUMN_STRIKES)));
game1.setSpares(cursor.getString(cursor.getColumnIndex(Game.COLUMN_SPARES)));
game1.setSplits(cursor.getString(cursor.getColumnIndex(Game.COLUMN_SPLITS)));
game1.setSplitConversions(cursor.getString(cursor.getColumnIndex(Game.COLUMN_SPLIT_CONVERSIONS)));
game1.setOpenFrames(cursor.getString(cursor.getColumnIndex(Game.COLUMN_OPEN_FRAMES)));
game1.setTimestamp(cursor.getString(cursor.getColumnIndex(Game.COLUMN_TIMESTAMP)));
games.add( game1 );
while (cursor.moveToNext());
//Close Database Connection
db.close();
//Return Game List
return games;
我在想，既然我使用上面的代码列出了投球手的所有游戏，我可以在将它们加载到列表视图时将分数相加。我将如何去完成这样的事情？
数据库助手
public class DatabaseHelper extends SQLiteOpenHelper
//Database Version
private static final int DATABASE_VERSION = 1;
//Database Name
private static final String DATABASE_NAME = "tpc_database";
public DatabaseHelper(Context context)
super(context, DATABASE_NAME, null, DATABASE_VERSION);
//Creating Tables
@Override
public void onCreate(SQLiteDatabase db)
db.execSQL(League.CREATE_TABLE);
db.execSQL(Bowler.CREATE_TABLE);
db.execSQL(Series.CREATE_TABLE);
db.execSQL(Game.CREATE_TABLE);
//Upgrade Database
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
//Drop Older Table If It Existed
db.execSQL("DROP TABLE IF EXISTS " + League.TABLE_NAME);
db.execSQL("DROP TABLE IF EXISTS " + Bowler.TABLE_NAME);
db.execSQL("DROP TABLE IF EXISTS " + Series.TABLE_NAME);
db.execSQL("DROP TABLE IF EXISTS " + Game.TABLE_NAME);
//Create Tables Again
onCreate( db );
//************************ ************************
//************************ League Methods ************************
//************************ ************************
public long insertLeague(String leagueName)
//Get Writable Database That We Want To Write Data Too
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
//`id` and `timestamp` Will Be Inserted Aromatically
values.put(League.COLUMN_NAME, leagueName);
//Insert Row
long id = db.insert(League.TABLE_NAME, null, values);
//Close Database Connection
db.close();
//Return Newly Inserted Row Id
return id;
public League getLeague(long id)
//Get Readable Database If We Are Not Inserting Anything
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.query(League.TABLE_NAME,
new String[]League.COLUMN_ID, League.COLUMN_NAME, League.COLUMN_TIMESTAMP,
League.COLUMN_ID + "=?",
new String[]String.valueOf(id), null, null, null, null);
if (cursor.moveToFirst())
//Prepare League Object
League league = new League(
cursor.getInt(cursor.getColumnIndex(League.COLUMN_ID)),
cursor.getString(cursor.getColumnIndex(League.COLUMN_NAME)),
cursor.getString(cursor.getColumnIndex(League.COLUMN_TIMESTAMP)));
//Close Database Connection
cursor.close();
return league;
else
return null;
public List<League> getAllLeagues()
List<League> leagues = new ArrayList<>();
//Select All Query
String selectQuery = "SELECT * FROM " + League.TABLE_NAME + " ORDER BY " +
League.COLUMN_TIMESTAMP + " DESC";
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
//Looping Through All Rows And Adding To The List
if (cursor.moveToFirst())
do
League league = new League();
league.setId(cursor.getInt(cursor.getColumnIndex(League.COLUMN_ID)));
league.setName(cursor.getString(cursor.getColumnIndex(League.COLUMN_NAME)));
league.setTimestamp(cursor.getString(cursor.getColumnIndex(League.COLUMN_TIMESTAMP)));
leagues.add(league);
while (cursor.moveToNext());
cursor.close();
//Close Database Connection
db.close();
//Return League List
return leagues;
public int getLeaguesCount()
String countQuery = "SELECT * FROM " + League.TABLE_NAME;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery(countQuery, null);
int count = cursor.getCount();
cursor.close();
//Return The Count
return count;
public int updateLeague(League league)
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put( League.COLUMN_NAME, league.getName() );
//Updating Row
return db.update(League.TABLE_NAME, values, League.COLUMN_ID + " = ?",
new String[]String.valueOf(league.getId()));
public void deleteLeague(League league)
SQLiteDatabase db = this.getWritableDatabase();
db.delete(League.TABLE_NAME, League.COLUMN_ID + " = ?",
new String[]String.valueOf( league.getId()));
db.close();
//************************ ************************
//************************ Bowler Methods ************************
//************************ ************************
public long insertBowler(String leagueId, String bowlerName)
//Get Writable Database That We Want To Write Data Too
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
//`id` and `timestamp` Will Be Inserted Automatically
values.put(Bowler.COLUMN_LEAGUE_ID, leagueId);
values.put(Bowler.COLUMN_NAME, bowlerName);
//Insert Row
//long id = db.insert(Bowler.TABLE_NAME, null, values);
long id = db.insertOrThrow( Bowler.TABLE_NAME, null, values );
Log.d("INSERTBOWLER","Number of bowlers in db = " + String.valueOf( DatabaseUtils.queryNumEntries(db,Bowler.TABLE_NAME)));
//Close Database Connection
db.close();
//Return Newly Inserted Row Id
return id;
public Bowler getBowler(String leagueId)
//Get Readable Database If We Are Not Inserting Anything
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.query( Bowler.TABLE_NAME,
new String[]Bowler.COLUMN_ID, Bowler.COLUMN_LEAGUE_ID, Bowler.COLUMN_NAME, Bowler.COLUMN_TIMESTAMP,
Bowler.COLUMN_LEAGUE_ID + "=?",
new String[]String.valueOf(leagueId), null, null, null, null);
Bowler bowler = null;
if (cursor.moveToFirst())
//Prepare Bowler Object
bowler = new Bowler(
cursor.getInt(cursor.getColumnIndex(Bowler.COLUMN_ID)),
cursor.getString(cursor.getColumnIndex(Bowler.COLUMN_LEAGUE_ID)),
cursor.getString(cursor.getColumnIndex(Bowler.COLUMN_NAME)),
cursor.getString(cursor.getColumnIndex(Bowler.COLUMN_TIMESTAMP)));
//Close Database Connection
cursor.close();
return bowler;
else
return bowler;
public List<Bowler> getAllBowlers(String leagueId)
List<Bowler> bowlers = new ArrayList<>();
//Select All Query
String selectQuery = "SELECT * FROM " + Bowler.TABLE_NAME + " WHERE " + Bowler.COLUMN_LEAGUE_ID + " = '" + leagueId + "'" + " ORDER BY " +
Bowler.COLUMN_TIMESTAMP + " DESC";
Log.d("GETALLBOWLERS-SQL","SQL used = >>>>" +selectQuery + "<<<<");
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
Log.d("GETALLBOWLERS-CNT","Number of rows retrieved = " + String.valueOf(cursor.getCount()));
//Looping Through All Rows And Adding To The List
if (cursor.moveToFirst())
do
Bowler bowler = new Bowler();
bowler.setId(cursor.getInt(cursor.getColumnIndex(Bowler.COLUMN_ID)));
bowler.setLeagueId(cursor.getString(cursor.getColumnIndex(Bowler.COLUMN_LEAGUE_ID)));
bowler.setName(cursor.getString(cursor.getColumnIndex(Bowler.COLUMN_NAME)));
bowler.setTimestamp(cursor.getString(cursor.getColumnIndex(Bowler.COLUMN_TIMESTAMP)));
bowlers.add(bowler);
while (cursor.moveToNext());
cursor.close();
//Close Database Connection
db.close();
Log.d("GETALLBOWLERS-CNT","Number of elements in bowlerslist = " + String.valueOf(bowlers.size()));
//Return Bowlers List
return bowlers;
public int getBowlersCount()
String countQuery = "SELECT * FROM " + Bowler.TABLE_NAME;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery(countQuery, null);
int count = cursor.getCount();
cursor.close();
//Return The Count
return count;
public int updateBowler(Bowler bowler)
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(Bowler.COLUMN_LEAGUE_ID, bowler.getLeagueId());
values.put(Bowler.COLUMN_NAME, bowler.getName());
//Updating Row
return db.update(Bowler.TABLE_NAME, values, Bowler.COLUMN_ID + " = ?",
new String[]String.valueOf(bowler.getId()));
public void deleteBowler(Bowler bowler)
SQLiteDatabase db = this.getWritableDatabase();
db.delete( Bowler.TABLE_NAME, Bowler.COLUMN_ID + " = ?",
new String[]String.valueOf( bowler.getId()));
db.close();
//************************ ************************
//************************ Series Methods ************************
//************************ ************************
public long insertSeries(String leagueId, String bowlerId, String seriesName)
//Get Writable Database That We Want To Write Data Too
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
//`id` and `timestamp` Will Be Inserted Automatically
values.put(Series.COLUMN_LEAGUE_ID, leagueId);
values.put(Series.COLUMN_BOWLER_ID, bowlerId);
values.put(Series.COLUMN_NAME, seriesName);
//Insert Row
//long id = db.insert( Series.TABLE_NAME, null, values );
long id = db.insertOrThrow( Series.TABLE_NAME, null, values );
Log.d("INSERT SERIES","Number of series in db = " + String.valueOf( DatabaseUtils.queryNumEntries(db,Series.TABLE_NAME)));
//Close Database Connection
db.close();
//Return Newly Inserted Row Id
return id;
public Series getSeries(String leagueId, String bowlerId)
//Get Readable Database If We Are Not Inserting Anything
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.query( Series.TABLE_NAME,
new String[]Series.COLUMN_ID, Series.COLUMN_LEAGUE_ID, Series.COLUMN_BOWLER_ID,
Series.COLUMN_NAME, Series.COLUMN_SERIES_AVERAGE, Series.COLUMN_TIMESTAMP,
Series.COLUMN_LEAGUE_ID + "=?" + " AND " + Series.COLUMN_BOWLER_ID + "=?",
new String[]String.valueOf(leagueId), String.valueOf(bowlerId), null, null, null, null);
if (cursor.moveToFirst())
//Prepare Series Object
Series series = new Series(
cursor.getInt(cursor.getColumnIndex(Series.COLUMN_ID)),
cursor.getString(cursor.getColumnIndex(Series.COLUMN_LEAGUE_ID)),
cursor.getString(cursor.getColumnIndex(Series.COLUMN_BOWLER_ID)),
cursor.getString(cursor.getColumnIndex(Series.COLUMN_NAME)),
cursor.getString(cursor.getColumnIndex(Series.COLUMN_SERIES_AVERAGE)),
cursor.getString(cursor.getColumnIndex(Series.COLUMN_TIMESTAMP)));
//Close Database Connection
cursor.close();
return series;
else
return null;
public List<Series> getAllSeries(String leagueId, String bowlerId)
List<Series> series = new ArrayList<>();
//Select All Query
String selectQuery = "SELECT * FROM " + Series.TABLE_NAME + " WHERE " + Series.COLUMN_LEAGUE_ID + " = '" + leagueId + "'" + " AND " + Series.COLUMN_BOWLER_ID + " = '" + bowlerId + "'"+ " ORDER BY " +
Series.COLUMN_TIMESTAMP + " DESC";
Log.d("GET ALL SERIES-SQL","SQL used = >>>>" +selectQuery + "<<<<");
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
Log.d("GET ALL SERIESS-CNT","Number of rows retrieved = " + String.valueOf(cursor.getCount()));
//Looping Through All Rows And Adding To The List
if (cursor.moveToFirst())
do
Series series1 = new Series();
series1.setId(cursor.getInt(cursor.getColumnIndex(Series.COLUMN_ID)));
series1.setLeagueId(cursor.getString(cursor.getColumnIndex(Series.COLUMN_LEAGUE_ID)));
series1.setBowlerId(cursor.getString(cursor.getColumnIndex(Series.COLUMN_BOWLER_ID)));
series1.setName(cursor.getString(cursor.getColumnIndex(Series.COLUMN_NAME)));
series1.setAverage(cursor.getString(cursor.getColumnIndex(Series.COLUMN_SERIES_AVERAGE)));
series1.setTimestamp(cursor.getString(cursor.getColumnIndex(Series.COLUMN_TIMESTAMP)));
series.add(series1);
while (cursor.moveToNext());
cursor.close();
//Close Database Connection
db.close();
Log.d("GETALLSERIES-CNT","Number of elements in serieslist = " + String.valueOf(series.size()));
//Return Series List
return series;
public int getSeriesCount()
String countQuery = "SELECT * FROM " + Series.TABLE_NAME;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery( countQuery, null );
int count = cursor.getCount();
cursor.close();
//Return The Count
return count;
public int updateSeries(Series series)
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(Series.COLUMN_LEAGUE_ID, series.getLeagueId());
values.put(Series.COLUMN_BOWLER_ID, series.getBowlerId());
values.put(Series.COLUMN_NAME, series.getName());
values.put(Series.COLUMN_SERIES_AVERAGE,series.getAverage());
//Updating Row
return db.update( Series.TABLE_NAME, values, Series.COLUMN_ID + " = ?",
new String[]String.valueOf( series.getId() ) );
public void deleteSeries(Series series)
SQLiteDatabase db = this.getWritableDatabase();
db.delete( Series.TABLE_NAME, Series.COLUMN_ID + " = ?",
new String[]String.valueOf( series.getId() ) );
db.close();
//************************ ************************
//************************ Game Methods ************************
//************************ ************************
public long insertGame(String leagueId, String bowlerId, String seriesId, String score, String strikes, String spares, String splits, String splitConversions, String openFrames)
//Get Writable Database That We Want To Write Data Too
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
//`id` and `timestamp` Will Be Inserted Automatically
values.put(Game.COLUMN_LEAGUE_ID, leagueId);
values.put(Game.COLUMN_BOWLER_ID, bowlerId);
values.put(Game.COLUMN_SERIES_ID, seriesId);
values.put(Game.COLUMN_SCORE, score);
values.put(Game.COLUMN_STRIKES, strikes);
values.put(Game.COLUMN_SPARES, spares);
values.put(Game.COLUMN_SPLITS, splits);
values.put(Game.COLUMN_SPLIT_CONVERSIONS, splitConversions);
values.put(Game.COLUMN_OPEN_FRAMES, openFrames);
//Insert Row
long id = db.insert( Game.TABLE_NAME, null, values );
//Close Database Connection
db.close();
//Return Newly Inserted Row Id
return id;
public Game getGame(String leagueId, String bowlerId, String seriesId)
//Get Readable Database If We Are Not Inserting Anything
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.query( Game.TABLE_NAME,
new String[]Game.COLUMN_ID, Game.COLUMN_LEAGUE_ID, Game.COLUMN_BOWLER_ID,
Game.COLUMN_SERIES_ID, Game.COLUMN_SCORE, Game.COLUMN_STRIKES, Game.COLUMN_SPARES, Game.COLUMN_SPLITS, Game.COLUMN_SPLIT_CONVERSIONS, Game.COLUMN_OPEN_FRAMES, Game.COLUMN_TIMESTAMP,
Game.COLUMN_LEAGUE_ID + "=?" + " AND " + Game.COLUMN_BOWLER_ID + "=?" + " AND " + Game.COLUMN_SERIES_ID + "=?",
new String[]String.valueOf( leagueId ), String.valueOf( bowlerId ), String.valueOf( seriesId ), null, null, null, null );
if (cursor.moveToFirst())
//Prepare Game Object
Game game = new Game(
cursor.getInt( cursor.getColumnIndex(Game.COLUMN_ID)),
cursor.getString( cursor.getColumnIndex(Game.COLUMN_LEAGUE_ID)),
cursor.getString( cursor.getColumnIndex(Game.COLUMN_BOWLER_ID)),
cursor.getString( cursor.getColumnIndex(Game.COLUMN_SERIES_ID)),
cursor.getString( cursor.getColumnIndex(Game.COLUMN_SCORE)),
cursor.getString( cursor.getColumnIndex(Game.COLUMN_STRIKES)),
cursor.getString( cursor.getColumnIndex(Game.COLUMN_SPARES)),
cursor.getString( cursor.getColumnIndex(Game.COLUMN_SPLITS)),
cursor.getString( cursor.getColumnIndex(Game.COLUMN_SPLIT_CONVERSIONS)),
cursor.getString( cursor.getColumnIndex(Game.COLUMN_OPEN_FRAMES)),
cursor.getString( cursor.getColumnIndex(Game.COLUMN_TIMESTAMP)));
//Close Database Connection
cursor.close();
return game;
else
return null;
public List<Game> getAllGames(String leagueId, String bowlerId, String seriesId)
List<Game> games = new ArrayList<>();
//Select All Query
String selectQuery = "SELECT * FROM " + Game.TABLE_NAME + " WHERE " + Game.COLUMN_LEAGUE_ID + " = '" + leagueId + "'" + " AND " + Game.COLUMN_BOWLER_ID + " = '" + bowlerId + "'" + " AND " + Game.COLUMN_SERIES_ID + " = '" + seriesId + "'" + " ORDER BY " +
Game.COLUMN_TIMESTAMP + " DESC";
try (SQLiteDatabase db = this.getWritableDatabase())
@SuppressLint("Recycle") Cursor cursor = db.rawQuery( selectQuery, null );
//Looping Through All Rows And Adding To The List
if (cursor.moveToFirst())
do
Game game1 = new Game();
game1.setId(cursor.getInt(cursor.getColumnIndex(Game.COLUMN_ID ) ) );
game1.setLeagueId(cursor.getString(cursor.getColumnIndex(Game.COLUMN_LEAGUE_ID)));
game1.setBowlerId(cursor.getString(cursor.getColumnIndex(Game.COLUMN_BOWLER_ID)));
game1.setSeriesId(cursor.getString(cursor.getColumnIndex(Game.COLUMN_SERIES_ID)));
game1.setScore(cursor.getString(cursor.getColumnIndex(Game.COLUMN_SCORE)));
game1.setStrikes(cursor.getString(cursor.getColumnIndex(Game.COLUMN_STRIKES)));
game1.setSpares(cursor.getString(cursor.getColumnIndex(Game.COLUMN_SPARES)));
game1.setSplits(cursor.getString(cursor.getColumnIndex(Game.COLUMN_SPLITS)));
game1.setSplitConversions(cursor.getString(cursor.getColumnIndex(Game.COLUMN_SPLIT_CONVERSIONS)));
game1.setOpenFrames(cursor.getString(cursor.getColumnIndex(Game.COLUMN_OPEN_FRAMES)));
game1.setTimestamp(cursor.getString(cursor.getColumnIndex(Game.COLUMN_TIMESTAMP)));
games.add( game1 );
while (cursor.moveToNext());
//Close Database Connection
db.close();
//Return Game List
return games;
public int getGameCount()
String countQuery = "SELECT * FROM " + Game.TABLE_NAME;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery( countQuery, null );
int count = cursor.getCount();
cursor.close();
//Return The Count
return count;
public int updateGame(Game game)
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(Game.COLUMN_LEAGUE_ID, game.getLeagueId());
values.put(Game.COLUMN_BOWLER_ID, game.getBowlerId());
values.put(Game.COLUMN_SERIES_ID, game.getSeriesId());
values.put(Game.COLUMN_SCORE, game.getScore());
values.put(Game.COLUMN_STRIKES, game.getStrikes());
values.put(Game.COLUMN_SPARES, game.getSpares());
values.put(Game.COLUMN_SPLITS, game.getSplits());
values.put(Game.COLUMN_SPLIT_CONVERSIONS, game.getSplitConversions());
values.put(Game.COLUMN_OPEN_FRAMES, game.getOpenFrames());
//Updating Row
return db.update( Game.TABLE_NAME, values, Game.COLUMN_ID + " = ?",
new String[]String.valueOf( game.getId() ) );
public void deleteGame(Game game)
SQLiteDatabase db = this.getWritableDatabase();
db.delete(Game.TABLE_NAME, Game.COLUMN_ID + " = ?",
new String[]String.valueOf( game.getId() ) );
db.close();
【问题讨论】：
【参考方案1】：sqlite> create table test (a int);
sqlite> insert into test values (1);
sqlite> insert into test values (2);
sqlite> insert into test values (3);
sqlite> insert into test values (4);
sqlite> select avg(a) as average, count(a) as count, sum(a) as sum from test;
average count sum
---------- ---------- ----------
2.5 4 10
sqlite> select avg(a) as average, count(a) as count, sum(a) as sum from test
where a > 2;
average count sum
---------- ---------- ----------
3.5 2 7
【讨论】：
是的，有很多core math functions。 我试图点击上面的链接，但我得到以下“未找到文档 文档 /lang_corefunc.html_ 在此服务器上不可用” 如何将 avg(col) 的结果分配给变量。 去掉 URL 末尾的下划线。您可以将查询的结果分配给一个变量，就像您在发布时所做的那样 - 它只是一个列值，就像其他任何东西一样。 如果 avg(col) 的结果只是表中的另一列，假设列名称是 avg 或 average 是否安全？【参考方案2】：我真的不明白你想要什么，但如果你想获得表格中所有列的平均值，请执行以下操作：
1 添加所有系列 ID。 （添加：将所有值放入一个数组并使用array_sum()）
2 使用mysqli_num_rows() 并计算表中的所有行数
如何取平均值：
将所有数字相加，然后除以有多少个数字。换句话说，它是总和除以计数。
3 将数组总和除以所有行数。
【讨论】：
我正在尝试获取 Game 表中与一系列 id 相对应的所有游戏的平均分数，然后将平均分数写入 Series 表以显示与匹配的特定系列游戏。 问题是关于 SQLite 的。以上是关于在 SQLite 中生成平均值的主要内容，如果未能解决你的问题，请参考以下文章
给定最小值、最大值、平均值和标准差，使用 Java 从分布中生成随机值