Question

我正在尝试根据IF条件更改where子句。查询由于某种原因失败。我将不胜感激任何帮助。

谢谢！

        SELECT
            c.id AS course,
            cr.id AS criteriaid,
            u.id AS userid,
            ue.timestart AS otimestart,
            (ue.timestart + cr.enrolperiod) AS ctimestart,
            ue.timecreated AS otimeenrolled,
            (ue.timecreated + cr.enrolperiod) AS ctimeenrolled
        FROM
            {user} u
        INNER JOIN
            {user_enrolments} ue
         ON ue.userid = u.id
        INNER JOIN
            {enrol} e
         ON e.id = ue.enrolid
        INNER JOIN
            {course} c
         ON c.id = e.courseid
        INNER JOIN
            {course_completion_criteria} cr
         ON c.id = cr.course
        LEFT JOIN
            {course_completion_crit_compl} cc
         ON cc.criteriaid = cr.id
        AND cc.userid = u.id
        WHERE
            cr.criteriatype = 5
        AND c.enablecompletion = 1
        AND cc.id IS NULL
        AND             
        (
        IF (ue.timeextension IS NULL)
                (ue.timestart > 0 AND ue.timestart + cr.enrolperiod < ?
          OR ue.timecreated > 0 AND ue.timecreated + cr.enrolperiod < ?)
        ELSE 
                (ue.timestart > 0 AND ue.timestart + ue.timextension < ?
          OR ue.timecreated > 0 AND ue.timecreated + ue.timeextension < ?)
        )

Answer 1

IF表达式的语法是：

IF(<cond-expr>, <then-expr>, <else-expr>)

语法中没有ELSE关键字，您只需用逗号分隔两个结果表达式。所以表达式的正确语法应该是：

AND IF(ue.timeextension IS NULL,
       (ue.timestart > 0 AND ue.timestart + cr.enrolperiod < ?)
         OR (ue.timecreated > 0 AND ue.timecreated + cr.enrolperiod < ?),
       (ue.timestart > 0 AND ue.timestart + ue.timextension < ?)
         OR (ue.timecreated > 0 AND ue.timecreated + ue.timeextension < ?))

另一种可以写这个的方法是：

AND ((ue.timestart > 0 AND ue.timestart + IFNULL(ue.timeextesion, cr.enrolperiod) < ?)
     OR (ue.timecreated > 0 AND ue.timecreated + IFNULL(ue.timeextesion, cr.enrolperiod)) < ?)

Answer 2

根据您要完成的内容，可能是正确的where子句：

...
where ...
and (if(ue.timeextension IS NULL,
        ue.timestart > 0 AND ue.timestart + cr.enrolperiod < ?
            OR ue.timecreated > 0 AND ue.timecreated + cr.enrolperiod < ?,
        ue.timestart > 0 AND ue.timestart + ue.timextension < ?
            OR ue.timecreated > 0 AND ue.timecreated + ue.timeextension < ?);

Answer 3

我想你可以尝试最后一节，即

   AND             
    (
    IF (ue.timeextension IS NULL)
            (ue.timestart > 0 AND ue.timestart + cr.enrolperiod < ?
      OR ue.timecreated > 0 AND ue.timecreated + cr.enrolperiod < ?)
    ELSE 
            (ue.timestart > 0 AND ue.timestart + ue.timextension < ?
      OR ue.timecreated > 0 AND ue.timecreated + ue.timeextension < ?)
    )

as

   AND             
    (
      (ue.timestart > 0 AND ue.timestart + 
             IFNULL(ue.timeextension , cr.enrolperiod )  < ? )
     OR (ue.timecreated > 0 AND ue.timecreated + 
             IFNULL (ue.timeextension, cr.enrolperiod) < ? )
    )

if-else在mysql中查询where子句

3 个答案: