add "fixed-column" option

[williamrowell]

For colname:value, add a column colname and populate with value.

The use case here is that I have a snakemake workflow that produces a lot of csv files with a structure like:
samples/<sample_id>/<condition_name>/this.csv
I want to import them all into the same table, where sample_id and condition_name are columns. I tried to match how --filename_column works, but allow for multiple new columns to be added.

I haven't yet added any tests, but if you think this option would be a useful addition, I will add some tests to cover the basic use case and the combination with shape.

[simonw]

I like this as a feature. I'd prefer it to use the following syntax though, rather than implementing its own split on the ::

csvs-to-sqlite test.csv test.db --fixed-column col1 foo --fixed-column col2 bar

Here's an example of an option in sqlite-utils that does this: https://github.com/simonw/sqlite-utils/blob/3b8abe608796e99e4ffc5f3f4597a85e605c0e9b/sqlite_utils/cli.py#L982-L987

The syntax for the decorator would look like this:

@click.option(
    "--fixed-column",
    multiple=True,
    type=(str, str),
    help="Populate column with a fixed value",
)

[williamrowell]

Realizing that casting the values as float or int probably isn't necessary.

[williamrowell]

I integrated the changes above and updated test_fixed_column to test all three options.

  --fixed-column <TEXT TEXT>...   Populate column with a fixed string
  --fixed-column-int <TEXT INTEGER>...
                                  Populate column with a fixed integer
  --fixed-column-float <TEXT FLOAT>...
                                  Populate column with a fixed float

This didn't work for a date column though:
--fixed-column created 20211116 --date created -df '%Y%m%d'

And the reason is a little confusing:
sqlite3.OperationalError: table test has no column named created

[simonw]

This looks great to me - I'll merge this in the morning!