Question

鉴于以下查询，如何对其进行优化以使子查询不依赖？

SELECT DISTINCT
    inst.id, inst.name, inst.state, inst.farm_status,
    (SELECT COUNT(inst_note.id) 
        FROM project_institution_note AS inst_note
        WHERE inst_note.institution_id = inst.id) AS inst_note_count,
    (SELECT COUNT(c.id) FROM project_catalog AS c
        WHERE c.institution_id = inst.id 
        AND c.status = 0 
        AND c.catalog_type BETWEEN 0 AND 1) AS ug_count,
    (SELECT COUNT(c.id) FROM project_catalog AS c
        WHERE c.institution_id = inst.id 
        AND c.status = 0 
        AND c.catalog_type BETWEEN 1 AND 2) AS grad_count,
    (SELECT COUNT(c.id) FROM project_catalog AS c
        WHERE c.institution_id = inst.id 
        AND c.status = 0 AND c.catalog_type >= 3) AS alt_count,
    (SELECT COUNT(c.id) FROM project_catalog_note AS cn
        INNER JOIN farmtool_catalog AS c
        ON c.id = cn.catalog_id
        WHERE c.institution_id = inst.id) AS catalog_note_count,
    (SELECT inst_note.text FROM project_institution_note AS inst_note
        LEFT JOIN project_institution AS inst
        ON inst_note.institution_id = inst.id
        WHERE inst_note.institution_id = inst.id
        ORDER BY inst_note.date DESC
        LIMIT 1) AS latest_note
FROM project_institution AS inst
LEFT JOIN project_institution_note AS inst_note
ON inst.id = inst_note.institution_id
LEFT JOIN project_catalog AS c
ON inst.id = c.institution_id
WHERE LOWER(inst.state) = "me";

我已尝试将第一个子查询重构为INNER JOIN，如此：

INNER JOIN (SELECT COUNT(inst_note.id) 
        FROM project_institution_note AS inst_note
        GROUP BY inst_note.institution_id) inst_note_count 
        ON inst_note.institution_id = inst.id

并在最后LEFT JOIN次操作后包含它，但返回空结果。

对我来说特别感兴趣的是优化计算ug_count和grad_count的第二和第三子查询。两者之间的唯一区别是第一个取决于（0,1）之间的字段值，以及（1,2）之间的第二个字段值。

现在，此查询运行正常，并且处于低使用率方案。不过，它显然效率很低，所以我希望尽可能优化。

Answer 1

这应该可以帮助你解决问题。

<div class="twelve wide stretched column" >
    <div class="ui tab segment active" data-tab="a">
    <div class="ui form">
        <div class="field">
          <label>Please Select Classroom</label>
          <select class="ui search dropdown" id="classroom">
           <option value="">Select Classroom</option>
          ';
        $faculty_id = $_SESSION["faculty_id"];
        $class = "select * from class where faculty=$faculty_id";
        $result = $conn->query($class);
        if ($result->num_rows > 0) {
            while ($fill = $result->fetch_assoc()) {
                $class_id = $fill['class_no'];
                $name = $fill['cls_name'];
                echo "<option value=$class_id>$name</option>";
            }
        }

 echo '
        </select>
        </div>
               ';
        echo'
        <div class="ui basic segment" style="display: none;" id="segment_course">
            <div class="field">
            <label>Please Select Course</label>
            <select class="ui search dropdown" id="course">
                 <option value="">Select Course</option>
          ';

        $faculty_id = $_SESSION["faculty_id"];
        $class = "select * from course where faculty=$faculty_id";
        $result = $conn->query($class);
        if ($result->num_rows > 0) {
            while ($fill = $result->fetch_assoc()) {
                $course_id = $fill['code_section'];
                $course_name = $fill['name'];
                echo "<option value=$course_id>$course_id - $course_name</option>";
            }
        }
echo '
            </select>
            </div>
        </div>
          <div class="ui basic segment" style="display: none;" id="segment_time">
                <div class="field">
                 <label>Please Select Course Start Time</label>
                 <select class="ui search dropdown" id="time">
                 <option value="">Select Start Time</option>
                 <option value="1">9:00-10:00</option>
                 <option value="2">10:00-11:00</option>
                 <option value="3">11:00-12:00</option>
                 <option value="4">12:00-13:00</option>
                 <option value="5">13:00-14:00</option>
                 <option value="6">14:00-15:00</option>
                 <option value="7">15:00-16:00</option>
                 <option value="8">16:00-17:00</option>
                 <option value="9">17:00-18:00</option>
                 <option value="10">18:00-19:00</option>
                 <option value="11">19:00-20:00</option>
                 <option value="12">20:00-21:00</option>
                </select>
                </div>
          </div>
          <div class="ui basic segment" style="display: none;" id="segment_duration">
              <div class="ui field">
                 <label>Please Enter Course Duration</label>
                <div class="ui fluid input">
                    <input type="text" placeholder="Duration of Course" id="duration">
                </div>
              </div>
          </div>
    </div>
</div>

不确定您是否可以采取任何有关获取最新笔记的信息。在Sql-Server中，我会使用cte和window函数，但这些东西在MySql中不可用。我希望无论如何这都很有用。

MySQL - 如何优化多个依赖子查询的查询以实现独立？

1 个答案: