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[[SQL]]中的<code>HAVING</code>子句规定：[[查询 (SQL)|SELECT语句]]仅返回聚合值（aggregate values）满足指定条件的行。<ref name="pgs23" />{{rp|125–127}}

== 用法==
初学者经常混淆<code>HAVING</code>和<code>WHERE</code>，但它们的作用阶段完全不同。<code>WHERE</code>在查询执行的早期阶段生效，用于过滤从表中读取的原始行。如果查询包含<code>GROUP BY</code>，系统会先对读取的行进行分组和聚合计算。在聚合操作之后，系统才会应用<code>HAVING</code>，过滤掉那些不符合指定条件的聚合行。因此，<code>WHERE</code>作用于从表中读取的数据，而<code>HAVING</code>仅应作用于聚合后的数据——因为在查询的初始阶段，这些聚合值（如总和、平均值）还是未知的。为了查看由<code>GROUP BY</code>子句生成的当前状态（Condition），通常会使用<code>HAVING</code>子句。
==示例==
若要查询2000年1月1日当天总销售额超过1000美元的部门ID列表及其销售额总和：
<syntaxhighlight lang="sql">
SELECT DeptID, SUM(SaleAmount)
FROM Sales
WHERE SaleDate = '2000-01-01'
GROUP BY DeptID
HAVING SUM(SaleAmount) > 1000
</syntaxhighlight>

以下查询将返回员工的人数超过1人的部门列表：
<syntaxhighlight lang="sql">
SELECT DepartmentName, COUNT(*)
FROM Employee
JOIN Department ON Employee.DepartmentID = Department.DepartmentID
GROUP BY DepartmentName
HAVING COUNT(*) > 1;
</syntaxhighlight>

使用<code>HAVING</code>非常方便，但并非必不可少。如果不用<code>HAVING</code>，实现上述示例等效功能的代码可能如下所示：
<syntaxhighlight lang="sql">
SELECT * FROM (
SELECT DepartmentName AS deptNam, COUNT(*) AS empCount
FROM Employee AS emp
JOIN Department AS dept ON emp.DepartmentID = dept.DepartmentID
GROUP BY deptNam
) AS grp
WHERE grp.empCount > 1;
</syntaxhighlight>

== 参考文献==
<references>

<ref name="pgs23">{{cite book |title=PostgreSQL 16.1 Documentation |year=2023 |publisher=The PostgreSQL Global Development Group |url=https://www.postgresql.org/files/documentation/pdf/16/postgresql-16-A4.pdf |access-date=2024-02-08 |archive-date=2026-03-11 |archive-url=https://web.archive.org/web/20260311020733/https://www.postgresql.org/files/documentation/pdf/16/postgresql-16-A4.pdf |dead-url=no }}</ref>

</references>

==外部链接==
*[http://www.databasejournal.com/features/mysql/article.php/3469351 The HAVING and GROUP BY SQL clauses] {{Webarchive|url=https://web.archive.org/web/20110603062905/http://www.databasejournal.com/features/mysql/article.php/3469351 |date=2011-06-03 }}
*[https://www.w3schools.com/sql/sql_functions.asp SQL Aggregate Functions] {{Webarchive|url=https://web.archive.org/web/20170503060710/https://www.w3schools.com/sql/sql_functions.asp |date=May 3, 2017 }}

{{SQL}}

[[Category:SQL]]

Having - 版本历史

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