sqlite-utils transform/insert --detect-types

[simonw]

Idea from simonw/datasette-edit-schema#13 - provide Python utility methods and accompanying CLI options for detecting the likely types of TEXT columns.

So if you have a text column that actually contained exclusively integer string values, it can let you know and let you run transform against it.

[simonw]

SQL query for detecting integers:

select
  'contains_non_integer' as result
from
  mytable
where
  cast(cast(mycolumn AS INTEGER) AS TEXT) != mycolumn
limit
  1

This will return a single row with a 1 as soon as it comes across a column that contains a non-integer - so it short circuits quickly on TEXT columns with non-integers in them.

If everything in the column is an integer it will scan the whole thing before returning no rows.

More extensive demo:

select
  value,
  cast(cast(value AS INTEGER) AS TEXT) = value as is_valid_int
from
  (
    select
      '1' as value
    union
    select
      '1.1' as value
    union
    select
      'dog' as value
    union
    select
      null as value
  )

https://latest.datasette.io/fixtures?sql=select%0D%0A++value%2C%0D%0A++cast%28cast%28value+AS+INTEGER%29+AS+TEXT%29+%3D+value+as+is_valid_int%0D%0Afrom%0D%0A++%28%0D%0A++++select%0D%0A++++++%271%27+as+value%0D%0A++++union%0D%0A++++select%0D%0A++++++%271.1%27+as+value%0D%0A++++union%0D%0A++++select%0D%0A++++++%27dog%27+as+value%0D%0A++++union%0D%0A++++select%0D%0A++++++null+as+value%0D%0A++%29

value	is_valid_int
1	1
1.1	0
dog	0

[simonw]

Posed a question about this on the SQLite forum here: https://sqlite.org/forum/forumpost/ab0dcd66ef

[simonw]

This recipe looks like it might be the way to detect floats:

select
  value,
  cast(cast(value AS REAL) AS TEXT) in (value, value || '.0') as is_valid_float
from
  (
    select
      '1' as value
    union
    select
      '1.1' as value
    union
    select
      'dog' as value
    union
    select
      null as value
  )

Demo: https://latest.datasette.io/fixtures?sql=select%0D%0A++value%2C%0D%0A++cast%28cast%28value+AS+REAL%29+AS+TEXT%29+in+%28value%2C+value+%7C%7C+%27.0%27%29+as+is_valid_float%0D%0Afrom%0D%0A++%28%0D%0A++++select%0D%0A++++++%271%27+as+value%0D%0A++++union%0D%0A++++select%0D%0A++++++%271.1%27+as+value%0D%0A++++union%0D%0A++++select%0D%0A++++++%27dog%27+as+value%0D%0A++++union%0D%0A++++select%0D%0A++++++null+as+value%0D%0A++%29

value	is_valid_float
1	1
1.1	1
dog	0

[simonw]

This work is going to happen in #282.