Re: Is it possible to decide the order of where conditions in Flink SQL

Posted by Tony Wei on
URL: http://deprecated-apache-flink-user-mailing-list-archive.369.s1.nabble.com/Is-it-possible-to-decide-the-order-of-where-conditions-in-Flink-SQL-tp29061p29068.html

Hi,

Thanks for your reply. I have tried both CTE and sql subquery, but it seems that sql plan

optimizer will do filter pushdown. Therefore, where conditions will end up being together in

physical plan.

However, the visualization of physical plans on Flink UI were different for these three SQL

query on their operations' name.

For the original SQL, it showed:

where: (AND(UDF_NEED_TO_QUERY_DB(user), NOT(user.is_robot))), select: (...)

For the CTE and subquery , it showed:

where: (AND(NOT(user.is_robot), UDF_NEED_TO_QUERY_DB(user))), select: (...)

Does this name for each operator of physical plan have any meaning to  represent the

execution order of `where` conditions?

Best,

Tony Wei

sri hari kali charan Tummala <[hidden email]> 於 2019年7月27日 週六 上午3:02寫道：

try cte common table expressions if it supports or sql subquery.

On Fri, Jul 26, 2019 at 1:00 PM Fanbin Bu <[hidden email]> wrote:

how about move query db filter to the outer select.

On Fri, Jul 26, 2019 at 9:31 AM Tony Wei <[hidden email]> wrote:

Hi,

If I have multiple where conditions in my SQL, is it possible to specify its order, so that the query 

can be executed more efficiently?

For example, if I have the following SQL, it used a heavy UDF that needs to access database.

However, if I can specify the order of conditions is executing `!user.is_robot` first then executing

UDF, it will reduce the number of database access. Those records with `true` in `user.is_robot` will

be dropped earlier and don't need to access database. 

select * 

from users

where !user.is_robot and UDF_NEED_TO_QUERY_DB(user)

Thanks,

Tony Wei 

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