獲取數和總數在mysql中加入2個表

Question

我在MySQL數據庫中的表2：

1.

p_code{ 
    code varchar(10) primary key, 
    discount decimal(4,2) not null, 
    valid_till date not null, 
    daily int not null, 
    total int non null, 
    max_amount decimal (6, 2) not null 
} 

2.

p_user{ 
    code varchar(10) not null, 
    email varchar(50) not null, 
    date date not null, 
    primary key (code, email, date), 
    foreign key (code) references p_code(code) 
} 

現在我想對於總共使用email多少次，總共使用多少次email以及的細節。

我曾嘗試以下查詢：

SELECT pc.discount, pc.valid, pc.daily, pc.total, pc.max_amount, c.tcount, c.count 
FROM p_code AS pc 
LEFT JOIN (

    SELECT t.code, t.email, t.tcount, p.count 
    FROM (

    SELECT code, email, COUNT(email) AS tcount 
    FROM p_user 
    GROUP BY code, email 
    ) AS t 
    LEFT JOIN (

    SELECT code, email, COUNT(email) AS count 
    FROM p_user 
    WHERE `date` = CURDATE() 
    GROUP BY code, email 
    ) AS p ON (t.code, t.email) = (p.code, p.email) 

) AS c ON pc.code = c.code 
WHERE c.email = ? 
AND pc.code = ? 

但問題是，如果我沒有在表中p_user爲code和email中的任何條目，它不返回任何行。

我要求它應該返回p_code的所有列以及tcount和count列的0和0。

Answer 1

我想你可以simplifiy查詢這樣了，反正你需要把狀態左側連接的數據......在左連接。

SELECT 
    c.discount, 
    c.valid, 
    c.daily, 
    c.total, 
    c.max_amount, 
    count(u.email) as totalCount, 
    sum(case when u.`date` = CURDATE() then 1 else 0 end) as dailyCount 
FROM p_code c 
LEFT JOIN p_user u on u.code = c.code and u.email = ? 
WHERE c.code = ? 
GROUP BY c.discount, c.valid, c.daily, c.total, c.max_amount 

你也可以做，對電子郵件的「過濾器」：

WHERE c.code = ? and (u.email is null or u.email = ?) 

Answer 2

您需要使用IFNULL函數。

IFNULL（表達式1，表達式2）

如果expr1不是NULL，IFNULL（）返回表達式1;否則返回 expr2。

您需要修改您的查詢，如：

SELECT pc.discount 
    , pc.valid 
    , pc.daily 
    , pc.total 
    , pc.max 
    , IFNULL(c.tcount, 0) AS tcount 
    , IFNULL(c.count, 0) as count 
FROM p_code AS pc 
...