Question

我正在尝试这样做，以便下面的查询计算来自另一个具有用户名的表的行，然后是具有杀手的死亡。统计信息表中每个用户名有1行，但pvp表中有多行用户名。出于某种原因，死亡列与杀戮列的数量相同，有谁知道为什么？这是我的查询。这是一个sql小提琴我想我得到了正确的idk如何使用sqlfiddle：http://sqlfiddle.com/#!2/b793b/1

SELECT 
    *,
    COUNT(pvptable.killer) as kills,   
    COUNT(pvptable.username) as deaths,
    ROUND(COUNT(pvptable.killer) / COUNT(pvptable.username), 2) as kd
FROM
    stats as st
    LEFT JOIN pvp as pvptable ON pvptable.killer=st.username
WHERE
    st.username="Username";

Answer 1

SELECT st.*,
       SUM(pvp.killer = st.username) AS kills,
       SUM(pvp.username = st.username) as deaths
FROM stats AS st
LEFT JOIN pvp ON pvp.username = st.username OR pvp.killer = st.username
WHERE st.username = "Username"

DEMO

要为所有人执行此操作，请使用GROUP BY：

SELECT st.*,
       SUM(pvp.killer = st.username) AS kills,
       SUM(pvp.username = st.username) as deaths
FROM stats AS st
LEFT JOIN pvp ON pvp.username = st.username OR pvp.killer = st.username
GROUP BY st.username

DEMO

Answer 2

COUNT(foo)和COUNT(bar)都会计算结果集中的行数，在这两种情况下您都可以说COUNT(*)。

例如，您需要COUNT(*) FROM ... GROUP BY killer来获取杀手的数量。不确定表结构是什么给你一个完整的答案。

MySQL LEFT JOIN查询显示相同的值

2 个答案: