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[GitHub] [airflow] jplauri opened a new pull request #19596: MsSqlHook: implement _generate_insert_sql
jplauri opened a new pull request #19596:
URL: https://github.com/apache/airflow/pull/19596
Related: https://github.com/apache/airflow/discussions/19583
For prepared SQL statements, MSSQL uses `?` rather than `%s` for parameter markers. Currently, [MsSqlHook](https://airflow.apache.org/docs/apache-airflow-providers-microsoft-mssql/stable/_api/airflow/providers/microsoft/mssql/hooks/mssql/index.html) does not provide an implementation of `_generate_insert_sql` used by `insert_rows` making it impossible to use for instance [GenericTransfer](https://airflow.apache.org/docs/apache-airflow/stable/_api/airflow/operators/generic_transfer/index.html) with the said hooks.
As written, the PR implements `_generate_insert_sql` for MsSqlHook but in a limited way. That is, it will only allow us to do INSERTs (so when `replace=False`) but not UPSERTs (when `replace=True`). I would love to get some feedback and ideas for implementing the UPSERT even though it is not useful for my current use-case.
Note that MSSQL does not support anything like "REPLACE INTO" for UPSERT. Instead, there seem to be two alternatives:
- Try to do an update first and check `@@ROWCOUNT`: in case nothing was updated, do an insert. This is explained [here by Aaron Bertrand](https://sqlperformance.com/2020/09/locking/upsert-anti-pattern).
- Use `MERGE`, many hits on StackOverflow such [this one](https://stackoverflow.com/q/2479488/551375) explaining the syntax.
It seems that Aaron B. argues for the pattern in the first link because of several issues with `MERGE` (see [list of issues](https://www.mssqltips.com/sqlservertip/3074/use-caution-with-sql-servers-merge-statement/)).
I spent a bit of time trying to implement either approach here, but got stuck after realizing it's not that straightforward to re-use parameter markers `?` from `values` from pyodbc `cursor.execute(sql, values)`. In any case, I was attempting to draw some inspiration from `_generate_insert_sql` of [PostgresHook](https://airflow.apache.org/docs/apache-airflow-providers-postgres/stable/_modules/airflow/providers/postgres/hooks/postgres.html#PostgresHook). Thus, this might need some work beyond just implementing `_generate_insert_sql` unless I'm missing something.
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[GitHub] [airflow] jplauri edited a comment on pull request #19596: MsSqlHook: implement _generate_insert_sql
Posted by GitBox <gi...@apache.org>.
jplauri edited a comment on pull request #19596:
URL: https://github.com/apache/airflow/pull/19596#issuecomment-970480520
> @jplauri regarding your question about merge vs insert, i think merge is the right call. That list of issues is pretty ancient now. Merge was implemented in 2008 and by now, I think most of the meaningful kinks have been ironed out. I would bet that the rowcount approach would be slow since it limits you to row-by-row (where as with merge you could, e.g. load into a temp table and merge into target with deduping logic too)
>
> But I don't think you need to tackle that in this PR. One thing at a time. Can do this limited case first.
Thanks! And yes, I would be fine with this limited solution too. I mean, GenericTransfer is meant to be used for small datasets anyway as it works in-mem, so I can imagine there are cases where doing say truncate & insert all is just fine instead of replace. Perhaps there are other use cases where replace is useful, but anyway.
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[GitHub] [airflow] jplauri commented on pull request #19596: MsSqlHook: implement _generate_insert_sql
Posted by GitBox <gi...@apache.org>.
jplauri commented on pull request #19596:
URL: https://github.com/apache/airflow/pull/19596#issuecomment-970480520
> @jplauri regarding your question about merge vs insert, i think merge is the right call. That list of issues is pretty ancient now. Merge was implemented in 2008 and by now, I think most of the meaningful kinks have been ironed out. I would bet that the rowcount approach would be slow since it limits you to row-by-row (where as with merge you could, e.g. load into a temp table and merge into target with deduping logic too)
>
> But I don't think you need to tackle that in this PR. One thing at a time. Can do this limited case first.
Thanks! And yes, I would be fine with this limited solution too. I mean, GenericTransfer is meant to be used for small datasets anyway as it works in-mem, so I can imagine there are cases where doing say truncate & insert all is just fine instead of replace.
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[GitHub] [airflow] eladkal commented on a change in pull request #19596: MsSqlHook: implement _generate_insert_sql
Posted by GitBox <gi...@apache.org>.
eladkal commented on a change in pull request #19596:
URL: https://github.com/apache/airflow/pull/19596#discussion_r795188792
##########
File path: tests/operators/test_generic_transfer.py
##########
@@ -26,6 +26,7 @@
from airflow.models.dag import DAG
from airflow.operators.generic_transfer import GenericTransfer
from airflow.providers.mysql.hooks.mysql import MySqlHook
+from airflow.providers.microsoft.mssql.hooks.mssql import MsSqlHook
Review comment:
```suggestion
from airflow.providers.microsoft.mssql.hooks.mssql import MsSqlHook
from airflow.providers.mysql.hooks.mysql import MySqlHook
```
To fix static tests
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[GitHub] [airflow] dstandish commented on pull request #19596: MsSqlHook: implement _generate_insert_sql
Posted by GitBox <gi...@apache.org>.
dstandish commented on pull request #19596:
URL: https://github.com/apache/airflow/pull/19596#issuecomment-970495398
> I mean, GenericTransfer is meant to be used for small datasets anyway as it works in-mem
Yeah I wasn't aware of that, this is my first look at generic transfer.
> so I can imagine there are cases where doing say truncate & insert all is just fine instead of replace
Yeah this is one of the challenges with trying to build an interface like this. Replace can mean "replace rows (i.e. when collision by PK)" or "replace table". And in the base implementation, it means by row. But you are talking by table. So there's ambiguity.
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[GitHub] [airflow] dstandish commented on pull request #19596: MsSqlHook: implement _generate_insert_sql
Posted by GitBox <gi...@apache.org>.
dstandish commented on pull request #19596:
URL: https://github.com/apache/airflow/pull/19596#issuecomment-970474540
@jplauri regarding your question about merge vs insert, i think merge is the right call. That list of issues is pretty ancient now. Merge was implemented in 2008 and by now, I think most of the meaningful kinks have been ironed out. I would bet that the rowcount approach would be slow since it limits you to row-by-row.
But I don't think you need to tackle that in this PR. One thing at a time. Can do this limited case first.
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[GitHub] [airflow] jplauri commented on pull request #19596: MsSqlHook: implement _generate_insert_sql
Posted by GitBox <gi...@apache.org>.
jplauri commented on pull request #19596:
URL: https://github.com/apache/airflow/pull/19596#issuecomment-983930377
@dstandish Not really sure if I got it right - I basically copied from TestPostgres with only superficial understanding. But intuitively it makes sense - running `test_mssql_to_mssql` will fail unless `_generate_insert_sql` is at least syntactically correct. What do you think?
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[GitHub] [airflow] dstandish commented on pull request #19596: MsSqlHook: implement _generate_insert_sql
Posted by GitBox <gi...@apache.org>.
dstandish commented on pull request #19596:
URL: https://github.com/apache/airflow/pull/19596#issuecomment-982677938
> @dstandish Would you be able to advise me further here
i'll review today
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[GitHub] [airflow] dstandish edited a comment on pull request #19596: MsSqlHook: implement _generate_insert_sql
Posted by GitBox <gi...@apache.org>.
dstandish edited a comment on pull request #19596:
URL: https://github.com/apache/airflow/pull/19596#issuecomment-970474540
@jplauri regarding your question about merge vs insert, i think merge is the right call. That list of issues is pretty ancient now. Merge was implemented in 2008 and by now, I think most of the meaningful kinks have been ironed out. I would bet that the rowcount approach would be slow since it limits you to row-by-row (where as with merge you could, e.g. load into a temp table and merge into target with deduping logic too)
But I don't think you need to tackle that in this PR. One thing at a time. Can do this limited case first.
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[GitHub] [airflow] uranusjr commented on pull request #19596: MsSqlHook: implement _generate_insert_sql
Posted by GitBox <gi...@apache.org>.
uranusjr commented on pull request #19596:
URL: https://github.com/apache/airflow/pull/19596#issuecomment-1012837301
Let’s see if tests can run now.
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[GitHub] [airflow] jplauri commented on pull request #19596: MsSqlHook: implement _generate_insert_sql
Posted by GitBox <gi...@apache.org>.
jplauri commented on pull request #19596:
URL: https://github.com/apache/airflow/pull/19596#issuecomment-979369199
@dstandish Would you be able to advise me further here, i.e., is there something more the PR should have? Should we just wait for a review/merge, or what's the process? I'm in no rush, but I believe this addition would be helpful for some people.
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[GitHub] [airflow] uranusjr commented on pull request #19596: MsSqlHook: implement _generate_insert_sql
Posted by GitBox <gi...@apache.org>.
uranusjr commented on pull request #19596:
URL: https://github.com/apache/airflow/pull/19596#issuecomment-1025506461
I merged main for #21221.
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[GitHub] [airflow] dstandish commented on pull request #19596: MsSqlHook: implement _generate_insert_sql
Posted by GitBox <gi...@apache.org>.
dstandish commented on pull request #19596:
URL: https://github.com/apache/airflow/pull/19596#issuecomment-970500140
Oh... _generate_insert_sql already _is_ row-by-row. I assumed it is row-based. Yeah in that case def small datasets / limited use cases.
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[GitHub] [airflow] boring-cyborg[bot] commented on pull request #19596: MsSqlHook: implement _generate_insert_sql
Posted by GitBox <gi...@apache.org>.
boring-cyborg[bot] commented on pull request #19596:
URL: https://github.com/apache/airflow/pull/19596#issuecomment-969059859
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