如何在 Oracle Developer 中使用 Count 功能
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How to utilize Count function in Oracle Developer
提问by Jeff
Ok so I'm working on my homework and am having trouble getting the Count function to work correctly.
好的，所以我正在做我的家庭作业并且无法让 Count 函数正常工作。
I am supposed to use "A query that lists all teams that have more than 4 players (in the players table). Include the columns team_id, team_name, and the count of players for that team."
我应该使用“一个查询，列出所有拥有超过 4 名球员的球队（在球员表中）。包括列 team_id、team_name 和该球队的球员人数。”
It is just a simple NHL database our teacher made up for this assignment. There are 18 teams in the teams database and 74 players in the players database.
这只是我们老师为这项作业制作的一个简单的 NHL 数据库。球队数据库中有18支球队，球员数据库中有74名球员。
This is what I have written as of right now:
这是我现在写的：
SELECT teams.team_id, teams.team_name, COUNT(players.team_id) AS PlayerCount
FROM teams, players
GROUP BY teams.team_id, teams.team_name
HAVING COUNT(players.team_id) > 4;
And when I run that this is the output I get:
当我运行时，这是我得到的输出：
TEAM_ID TEAM_NAME PLAYERCOUNT
------- ----------------------------------- ----------------------
TBL Tampa Bay Lightening 74
BOS Bostong Bruins 74
SJS San Jose Sharks 74
NYI New York Islanders 74
MIN Minnesota Wild 74
DET Detroit Red Wings 74
NYR New York Rangers 74
PHL Philadelphia Flyers 74
BUF Buffalo Bruins 74
PIT Pittsburgh Penguins 74
DAL Dallas Stars 74
VAN Vancouver Canucks 74
WSH Washington Capitals 74
COL Colorado Avalanche 74
TOR Toronto Maple Leafs 74
CLB Columbus Blue Hymanets 74
CHI Chicago Blackhawks 74
ATL Atlanta Thrashers 74
18 rows selected
I know it's probably pretty simple to fix, but I can't find anything that's like that in my textbook and the Google results I get are either not the same thing or more sophisticated than what I am trying to do.
我知道修复它可能很简单，但我在我的教科书中找不到任何类似的东西，而且我得到的谷歌结果要么不一样，要么比我想要做的更复杂。
Any help is greatly appreciated.
任何帮助是极大的赞赏。
回答by Jeffrey Kemp
You're doing a cartesian join between the tables.
您正在表之间进行笛卡尔连接。
SELECT teams.team_id, teams.team_name, COUNT(*) AS PlayerCount
FROM teams, players
WHERE teams.team_id = players.team_id
GROUP BY teams.team_id, teams.team_name
HAVING COUNT(*) > 4;
