[英]How can I write this postgres query in Amazon redshift such that it is as optimized as it was in postgres?
这是我在postgres中使用的原始查询-
SELECT a.id,
(SELECT val
FROM database.detail x
WHERE name = 'blablah'
AND x.id = b.id) AS myGroup,
c.username,
a.someCode,
a.timeTaken,
a.date ::timestamp WITH time ZONE AT time ZONE 'PST' AS date,
SUM (CASE WHEN (b.name = 'name1') THEN b.val ::INTEGER ELSE 0 END ) AS name11,
SUM (CASE WHEN (b.name = 'name2') THEN b.val ::INTEGER ELSE 0 END ) AS name12
FROM
database.myTable a,
database.detail b,
database.client c
WHERE
a.id = b.id
AND a.c_id = c.c_id
AND a.date > current_date - interval '2 weeks'
GROUP BY 1, 2, 3, 4, 5, 6
以下是我如何将此查询转换为Amazon redshift查询。
SELECT a.id,
b.val AS myGroup,
c.username,
a.someCode,
a.timeTaken,
convert_timezone('PST', a.date) AS date,
SUM (CASE WHEN (b.name = 'name1') THEN b.val ::INTEGER ELSE 0 END ) AS name11,
SUM (CASE WHEN (b.name = 'name2') THEN b.val ::INTEGER ELSE 0 END ) AS name12
FROM
database.myTable a,
database.detail b,
database.client c
WHERE
a.id = b.id
AND b.name = 'blablah'
AND a.c_id = c.c_id
AND a.date > current_date - interval '2 weeks'
GROUP BY 1, 2, 3, 4, 5, 6 LIMIT 10
CASE语句似乎没有按照预期的方式执行,基本上name11和name12的值都为零。 我的postgres查询返回了这些的有效值,但redshift查询却没有。
另外,此查询非常慢。 Postgres查询大约需要150毫秒,而此查询则需要2分钟。
我们怎样才能做得更好?
Redshift查询优化来自表的群集,表设计,数据加载,数据清理和分析。
让我回答上面列表中的一些核心接触点。 1.确保您的表可更改,详细,客户端具有正确的SORT_KEY,DIST_KEY。2.确保您对联接中的所有表进行正确的分析和清理。
这是用Redshift格式编写的同一SQL的另一个版本。
我做了几项调整
我的Redshift SQL版本
/** Date Range Computation **/
with date_range as (
select ( current_Date - interval '2 weeks' ) as two_weeks
),
/** Filter main ResultSet**/
myGroupSet as (
SELECT b.val AS myGroup,
c.username,
a.someCode,
a.timeTaken,
(case when (b.name == 'name1') THEN b.val::INTEGER ELSE 0 END ) as name11,
(case when (b.name == 'name2') THEN b.val::INTEGER ELSE 0 END ) as name12
FROM database.myTable a,
join date_range dr on a.date > dr.two_weeks
join database.detail b on b.id = a.id
join database.client c on c.c_id = a.c_id
where a.date > current_Date - interval '2 weeks'
)
/** Apply Aggregation **/
select myGroup, username, someCode, timeTaken, date,
sum(name1), sum(name2)
from myGroupSet
group by myGroup, username, someCode, timeTaken, date
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