feat: add to_date function to StringValue

[saschahofmann]

Description of changes

• Adds to_date to string types that accepts a format string and parses a string to Date type.

• Uses a cast to timestamp and extract time as a fallback like this

def visit_StringToDate(self, op, *, arg, format_str):
        return self.f.date(self.f.str_to_time(arg, format_str))

• Implements native functions for bigquery, clickhouse, MySQL, oracle, postgres, and snowflake

Issues closed

Implements half of #8908

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[saschahofmann]

@gforsyth I am struggling a little with running the tests. I couldn't find much on setting up the database. I can see that in conftest.py some env variable are read so I provided those for my local postgres database via the .env file (on a side note: I found it weird that the .env is committed? )

Now I seem to be missing an extension

psycopg2.errors.UndefinedFile: could not open extension control file "/opt/homebrew/share/postgresql@14/extension/plpython3u.control": No such file or directory

and it doesn't seem trivial to install it. Is there any documentation on setting up the env for running the tests?

[gforsyth]

Hey @saschahofmann -- rather than using your own instance, I'd recommend installing just and running just up postgres.
That will spin up a postgres container with all the extensions needed and at the port that our pytest setup expects by default.

[gforsyth]

There are also some instructions here: https://ibis-project.org/contribute/02_workflow#running-the-test-suite

If you're using a mac M2 it's more involved because of the architecture

[saschahofmann]

Perfect. No idea why i didnt find that section. Will experiment around and hopefully have something more complete soon.

[saschahofmann]

I now implemented the default fallback in sql/compiler.py L804 like this

def visit_StringToDate(self, op, *, arg, format_str):
        return self.f.date(self.f.str_to_time(arg, format_str))

Is there a way to do it using ibis (something like to_timestamp().date(). Also I was thinking whether SQLGlot might have implemented it for its dialect already similar to how its done for str_to_time but I couldn't find it. In the meantime, I am implementing the different cases for the backends separately.

[saschahofmann]

For postgres, the format for to_timestamp seems to be translated to the postgres native format but its not obvious to me where this happens? I would need to do something similar for to_date

[gforsyth]

@saschahofmann -- sqlglot handles the timestamp formatting here: https://github.com/tobymao/sqlglot/blob/d3472c664fdfb7c9cfa9a54c6b0491b605cf4913/sqlglot/dialects/postgres.py#L186-L193

[saschahofmann]

Alright. I found that SQLGlot has actually implemented StrToDate so I am just using that. What do I need to do make the doc test pass?

[saschahofmann]

I think its ready for review !

[gforsyth]

This looks really nice, @saschahofmann !

I think this patch will get snowflake passing:

index 75bfd7ce6..c0915d059 100644
--- a/ibis/backends/snowflake/compiler.py
+++ b/ibis/backends/snowflake/compiler.py
@@ -78,6 +78,7 @@ class SnowflakeCompiler(SQLGlotCompiler):
         ops.Hash: "hash",
         ops.Median: "median",
         ops.Mode: "mode",
+        ops.StringToDate: "to_date",
         ops.StringToTimestamp: "to_timestamp_tz",
         ops.TimeFromHMS: "time_from_parts",
         ops.TimestampFromYMDHMS: "timestamp_from_parts",

[saschahofmann]

Huh, I think I actually had this but removed it because I thought it was in SQLGlot. Will put it back

[saschahofmann]

I assume that the failing test is unrelated? At least its not clear to me where this would be coming from?

[gforsyth]

Thanks for putting this together @saschahofmann! The snowpark error is definitely unrelated and might be flaky, so I'm going to merge this and see what happens on CI.