HAVING 子句
HAVING子句用来控制查询中分组的选择，与聚合函数和GROUP BY子句一起使用。HAVING子句的功能会在分组和聚合计算完成后进行，过滤掉不满足条件的分组。
下面的示例将账户结余大于 5700000 的用户选出来：
SELECT count(*), mktsegment, nationkey,
CAST(sum(acctbal) AS bigint) AS totalbal
FROM customer
GROUP BY mktsegment, nationkey
HAVING sum(acctbal) > 5700000
ORDER BY totalbal DESC;
输出如下：
_col0 | mktsegment | nationkey | totalbal
-------+------------+-----------+----------
1272 | AUTOMOBILE | 19 | 5856939
1253 | FURNITURE | 14 | 5794887
1248 | FURNITURE | 9 | 5784628
1243 | FURNITURE | 12 | 5757371
1231 | HOUSEHOLD | 3 | 5753216
1251 | MACHINERY | 2 | 5719140
1247 | FURNITURE | 8 | 5701952
(7 rows)
