在 SQL 语句中除以零如何避免特定记录 returns 除以零

Question

我想发表一个声明，将球员的进球数除以比赛场数。如果玩家玩了 0 场比赛，将发生 0 分。我如何“跳过”或忽略它并显示 N/A 而不是每场比赛的进球数？这是我目前拥有的：

SELECT PlayerName, PlayerSurname, GamesPlayed, GoalsScored, ROUND(GoalsScored/GamesPlayed ,2) AS GoalsPerGame
FROM tblPlayers , tblStatistics 
WHERE tblPlayers.PlayerID = tblStatistics.PlayerID 
ORDER BY GoalsScored DESC

我在 delphi 10.3 中这样做，所以表的连接是在 where 语句中完成的，但这不会影响一般问题。如果我为一张唱片做这件事，我会做的

if tblStatistics['GamesPlayed'] = 0 then
begin
qryStatsStatic.SQL.Clear;
qryStatsStatic.SQL.Add('
SELECT PlayerName, PlayerSurname, GamesPlayed, GoalsScored, "N/A" AS GoalsPerGame
FROM tblPlayers , tblStatistics 
WHERE tblPlayers.PlayerID = tblStatistics.PlayerID 
ORDER BY GoalsScored DESC');
qryStatistics.open;
end;

但我的问题是多条记录。

Answer 1

SQL 具有 CASE 语句，该语句仅在找到匹配项之前执行。

CASE WHEN COALESCE(GamesPlayed,0) = 0 THEN 0
     ELSE ROUND(GoalsScored/GamesPlayed,2) 
END AS GoalsPerGame

每场比赛的进球数也是 goals/games。

Answer 2

您可以使用大多数流行的 DBMS 中都存在的简短 nullif 函数：

select
  ...,
  ROUND(GamesPlayed/nullif(GoalsScored, 0) ,2) as GoalsPerGame
...

Answer 3

尝试 SQL 联盟：

SELECT PlayerName, PlayerSurname, GamesPlayed, GoalsScored, 
       ROUND(GamesPlayed/GoalsScored ,2) AS GoalsPerGame
FROM tblPlayers , tblStatistics 
WHERE tblPlayers.PlayerID = tblStatistics.PlayerID
  AND GoalsScored <> 0
UNION
SELECT PlayerName, PlayerSurname, GamesPlayed, GoalsScored, 0
FROM tblPlayers , tblStatistics 
WHERE tblPlayers.PlayerID = tblStatistics.PlayerID
  AND GoalsScored = 0
ORDER BY GoalsScored DESC

在 SQL 语句中除以零如何避免特定记录 returns 除以零

Division by zero in SQL statement how to avoid specific record if it returns division by zero

sql

delphi