如何解决无法获取SELECT返回的多行以按特定列正确汇总
我有一个看起来像这样的Oracle表：
test_time test_name test_type test_location test_value
----------------- --------- --------- ------------- ----------
09/22/20 12:00:05 A RT Albany 200
09/22/20 12:00:05 A RT Chicago 500
09/22/20 12:00:05 B RT Albany 400
09/22/20 12:00:05 B RT Chicago 300
09/22/20 12:00:05 A WPL Albany 1500
09/22/20 12:00:05 A WPL Chicago 2300
09/22/20 12:00:05 B WPL Albany 2100
09/22/20 12:00:05 B WPL Chicago 1900
09/22/20 12:05:47 A RT Albany 300
09/22/20 12:05:47 A RT Chicago 400
09/22/20 12:05:47 B RT Albany 600
09/22/20 12:05:47 B RT Chicago 500
09/22/20 12:05:47 A WPL Albany 1700
09/22/20 12:05:47 A WPL Chicago 2000
09/22/20 12:05:47 B WPL Albany 1800
09/22/20 12:05:47 B WPL Chicago 2400
我想对该表运行SELECT，它将显示过去11分钟内为特定test_type（在本例中为“ RT”）引用的每个位置的平均值，并以test_name进行汇总。 “ 11分钟”用于确保我至少从每五分钟插入一次记录的脚本的两次迭代中检索行。
我希望针对此表的SELECT语句的结果如下所示：
test_name albany_avg_val chicago_avg_val
--------- -------------- ---------------
A 250 450
B 500 400
（注意：test_name“ A”的“ albany_avg_val”反映了与test_name“ A” / test_type“ RT” / test_location“ Albany”的两次迭代关联的“ test_value”值的平均值： 00和12:05）。
我到目前为止构建的SELECT语句如下：
SELECT
test_name,CASE test_location
WHEN 'Albany'
THEN ROUND(AVG( test_value ),0) albany_avg_val
WHEN 'Chicago'
THEN ROUND(AVG( test_value ),0) chicago_avg_val
END
FROM
test_table
WHERE
test_type = 'RT' AND test_time > sysdate - interval '11' minute;
...但是它没有按预期工作。有人可以帮我解决我可能会缺少的东西吗？
解决方法
我想你想要
select
test_name,round(avg(case when test_location = 'Albany' then test_value end)) albany_avg_val
round(avg(case when test_location = 'Chicago' then test_value end)) chicago_avg_val
from test_table
where
test_type = 'rt'
and test_location in ('Albany','Chicago')
and test_time > sysdate - 11 / 24 / 60
group by test_name
也就是说：
-
使用
group by！ -
在聚合函数
case中移动avg()表达式 -
每列应分开-条件表达式不能生成两列
还有...：
-
预过滤可提高查询效率
-
对于
sysdate（它是date）使用“数字”日期算术比较安全；如果要区间算术，请改用systimestamp -
0是round()的默认精度
where子句中的似乎您需要条件聚合：
SELECT
test_name,AVG(CASE
WHEN test_location='Albany'
THEN ROUND( test_value ) END) AS albany_avg_val,AVG(WHEN test_location='Chicago'
THEN ROUND( test_value ) END) AS chicago_avg_val
FROM test_table
WHERE test_type = 'RT'
AND test_time > sysdate - interval '11' minute;
GROUP BY test_name
0函数的 第二个参数（ROUND()）是多余的。
请尝试这样的事情
SELECT
test_name,ROUND(AVG(CASE when test_location='Albany'
THEN test_value
else null end),0) albany_avg_val,ROUND(AVG(CASE when test_location='Chicago'
THEN test_value
else null end),0) Chicago_avg_val
FROM
test_table
WHERE
test_type = 'RT' AND test_time > sysdate - interval '11' minute
group by test_name; ```
pivot子句正是针对此类情况而设计的：以下查询汇总了所有test_type值：
select *
from (select test_name,test_location,test_type,test_value from test_table)
pivot(
avg(test_value)
for test_location in ('Albany ' as Albany,'Chicago' as Chicago)
);
结果：
TEST_NAME TEST_TYPE ALBANY CHICAGO
--------- --------- ---------- ----------
A RT 250 450
B RT 500 400
A WPL 1600 2150
B WPL 1950 2150
或者如果您只想过滤RT：
select *
from (select test_name,test_value from test_table where test_type='RT')
pivot(
avg(test_value)
for test_location in ('Albany ' as Albany,'Chicago' as Chicago)
);
结果：
TEST_NAME ALBANY CHICAGO
--------- ---------- ----------
B 500 400
A 250 450
带有示例数据的完整测试用例：
with test_table(test_time,test_name,test_value) as (
select to_date('09/22/20 12:00:05','mm/dd/yy hh24:mi:ss'),'A','RT ','Albany ',200 from dual union all
select to_date('09/22/20 12:00:05','Chicago',500 from dual union all
select to_date('09/22/20 12:00:05','B',400 from dual union all
select to_date('09/22/20 12:00:05',300 from dual union all
select to_date('09/22/20 12:00:05','WPL',1500 from dual union all
select to_date('09/22/20 12:00:05',2300 from dual union all
select to_date('09/22/20 12:00:05',2100 from dual union all
select to_date('09/22/20 12:00:05',1900 from dual union all
select to_date('09/22/20 12:05:47',300 from dual union all
select to_date('09/22/20 12:05:47',400 from dual union all
select to_date('09/22/20 12:05:47',600 from dual union all
select to_date('09/22/20 12:05:47',500 from dual union all
select to_date('09/22/20 12:05:47',1700 from dual union all
select to_date('09/22/20 12:05:47',2000 from dual union all
select to_date('09/22/20 12:05:47',1800 from dual union all
select to_date('09/22/20 12:05:47',2400 from dual
)
select *
from (select test_name,'Chicago' as Chicago)
);
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