Question

我（至少对我而言）有一个复杂的查询，该查询是使用此站点中的示例构建的。我添加的最后一件事是IF语句。如果没有IF语句，它将使用IF语句的TRUE部分。我希望你们的女孩/家伙可以在这里帮助我。这是查询：

SELECT 
    t.ID, t.start_time, t.end_time, t.start_date, t.end_date, t.balance, 
    u1.first_name AS teacher_one_first_name, u1.last_name AS teacher_one_last_name, 
    u2.first_name AS teacher_two_first_name, u2.last_name AS teacher_two_last_name,
    company.name, company.post_city, tag, lvl,
    IF(
        t.balance=1,
        (
            (SELECT count(user_ID)
                FROM company_lesson_block_student
                WHERE lead_follow=0 AND company_lesson_block_ID=t.ID) AS lead,
            (SELECT count(user_ID)
                FROM company_lesson_block_student
                WHERE lead_follow=1 AND company_lesson_block_ID=t.ID) AS follow
        ),
            (SELECT count(user_ID)
                FROM company_lesson_block_student
                WHERE company_lesson_block_ID=t.ID) AS total_student
    )
    FROM company_lesson_block AS t
    LEFT JOIN company_lvl ON company_lvl.ID = t.lvl_ID
    LEFT JOIN tag ON tag.ID = t.style_ID
    LEFT JOIN company ON company.ID=t.location_ID
    LEFT JOIN user AS u1 ON t.teacher_one_ID=u1.ID
    LEFT JOIN user AS u2 ON t.teacher_two_ID=u2.ID
    WHERE t.company_ID='1' AND location_ID='1' AND company_season_ID='1'
    ORDER BY start_date ASC

我收到的错误消息是：

您的SQL语法有错误；检查与您的MariaDB服务器版本相对应的手册为在“ AS线索”附近使用正确的语法，（在第10行选择（SELECT count（user_ID）FROM company_less）

任何帮助/提示都适用

Answer 1

您想返回2列，但是IF只能返回1，因此您需要2个IF：

........................
IF(
    t.balance=1,
        (SELECT count(user_ID)
            FROM company_lesson_block_student
            WHERE lead_follow=0 AND company_lesson_block_ID=t.ID),
        (SELECT count(user_ID)
            FROM company_lesson_block_student
            WHERE company_lesson_block_ID=t.ID)
) AS ????,
IF(
    t.balance=1,
       (SELECT count(user_ID)
            FROM company_lesson_block_student
            WHERE lead_follow=1 AND company_lesson_block_ID=t.ID),
        (SELECT count(user_ID)
            FROM company_lesson_block_student
            WHERE company_lesson_block_ID=t.ID)
) AS ????
........................

必须在IF的右括号后面设置别名。
也许您必须重新考虑此逻辑，因为对于FALSE，相同的值将返回两次。

使用IF语句和子查询的mysql查询中的错误

1 个答案: