MySQL5.7计算两表列总和差值插入目标表报SQL语法错误如何解决

• 违反SELECT语句语法规则：SELECT子句仅用于定义返回的列表达式，不能将FROM表声明拆分到每个字段的运算逻辑中，原代码把FROM communities、FROM daily_shares嵌入列的减法运算，不符合MySQL语法要求。
• 存在逻辑笔误：所有字段的减法右侧都错误写为SUM(shares_copylink) FROM daily_shares，没有和左侧communities表的对应字段匹配，计算逻辑完全错误。
• 查询结构缺失：整段SELECT语句没有声明主查询的FROM表，WHERE子句的位置也不符合语法规范。

INSERT INTO shares_diff (
    `date`, 
    `shares_copylink`, 
    `shares_email`, 
    `shares_facebook`, 
    `shares_messenger`, 
    `shares_pinterest`, 
    `shares_twitter`, 
    `shares_whatsapp`
)
SELECT 
    CURDATE() AS `date`,
    c.total_copylink - IFNULL(d.total_copylink, 0) AS shares_copylink,
    c.total_email - IFNULL(d.total_email, 0) AS shares_email,
    c.total_facebook - IFNULL(d.total_facebook, 0) AS shares_facebook,
    c.total_messenger - IFNULL(d.total_messenger, 0) AS shares_messenger,
    c.total_pinterest - IFNULL(d.total_pinterest, 0) AS shares_pinterest,
    c.total_twitter - IFNULL(d.total_twitter, 0) AS shares_twitter,
    c.total_whatsapp - IFNULL(d.total_whatsapp, 0) AS shares_whatsapp
FROM (
    -- 统计communities表所有分享字段的总和
    SELECT 
        SUM(shares_copylink) AS total_copylink,
        SUM(shares_email) AS total_email,
        SUM(shares_facebook) AS total_facebook,
        SUM(shares_messenger) AS total_messenger,
        SUM(shares_pinterest) AS total_pinterest,
        SUM(shares_twitter) AS total_twitter,
        SUM(shares_whatsapp) AS total_whatsapp
    FROM communities
) AS c
LEFT JOIN (
    -- 统计daily_shares表所有分享字段的总和
    SELECT 
        SUM(shares_copylink) AS total_copylink,
        SUM(shares_email) AS total_email,
        SUM(shares_facebook) AS total_facebook,
        SUM(shares_messenger) AS total_messenger,
        SUM(shares_pinterest) AS total_pinterest,
        SUM(shares_twitter) AS total_twitter,
        SUM(shares_whatsapp) AS total_whatsapp
    FROM daily_shares
) AS d ON 1=1
-- 保留原逻辑：仅当daily_shares表存在数据时执行插入
WHERE EXISTS (SELECT * FROM daily_shares);

内容的提问来源于stack exchange，提问作者Revolucion for Monica