html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,issue,performed_via_github_app
https://github.com/simonw/sqlite-utils/issues/186#issuecomment-709705624,https://api.github.com/repos/simonw/sqlite-utils/issues/186,709705624,MDEyOklzc3VlQ29tbWVudDcwOTcwNTYyNA==,9599,2020-10-16T03:14:39Z,2020-10-16T03:14:39Z,OWNER,"How should this work with extractions covering multiple columns?

If there's a single column then it makes sense that a `null` value would not be extracted into the lookup table, but would instead become stay as `null`.

For a multiple column extraction, provided at least one of those columns is not null It should map to a record in the lookup table. Only if ALL of the extracted columns are null should the lookup value stay null.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",722816436,
https://github.com/simonw/sqlite-utils/issues/186#issuecomment-709705885,https://api.github.com/repos/simonw/sqlite-utils/issues/186,709705885,MDEyOklzc3VlQ29tbWVudDcwOTcwNTg4NQ==,9599,2020-10-16T03:15:39Z,2020-10-16T03:15:39Z,OWNER,The alternative solution here would be that a single `null` value DOES get extracted. To implement this I would need to add some logic that uses `is null` instead of `=`.,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",722816436,
https://github.com/simonw/sqlite-utils/issues/186#issuecomment-709706065,https://api.github.com/repos/simonw/sqlite-utils/issues/186,709706065,MDEyOklzc3VlQ29tbWVudDcwOTcwNjA2NQ==,9599,2020-10-16T03:16:22Z,2020-10-16T03:16:22Z,OWNER,Either way I think I'm going to need to add some SQL which uses `where a = b or (a is null and b is null)`.,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",722816436,
https://github.com/simonw/sqlite-utils/issues/186#issuecomment-709706260,https://api.github.com/repos/simonw/sqlite-utils/issues/186,709706260,MDEyOklzc3VlQ29tbWVudDcwOTcwNjI2MA==,9599,2020-10-16T03:17:02Z,2020-10-16T03:17:17Z,OWNER,Actually I think this should be an option to `.extract()` which controls if nulls are extracted or left alone. Maybe called `extract_nulls=True/False`.,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",722816436,
https://github.com/simonw/sqlite-utils/issues/186#issuecomment-710198162,https://api.github.com/repos/simonw/sqlite-utils/issues/186,710198162,MDEyOklzc3VlQ29tbWVudDcxMDE5ODE2Mg==,9599,2020-10-16T16:41:00Z,2020-10-16T16:41:00Z,OWNER,"Failing test:
```python
def test_extract_null_values(fresh_db):
    fresh_db[""species""].insert({""id"": 1, ""species"": ""Wolf""}, pk=""id"")
    fresh_db[""individuals""].insert_all(
        [
            {""id"": 10, ""name"": ""Terriana"", ""species"": ""Fox""},
            {""id"": 11, ""name"": ""Spenidorm"", ""species"": None},
            {""id"": 12, ""name"": ""Grantheim"", ""species"": ""Wolf""},
            {""id"": 13, ""name"": ""Turnutopia"", ""species"": None},
            {""id"": 14, ""name"": ""Wargal"", ""species"": ""Wolf""},
        ],
        pk=""id"",
    )
    fresh_db[""individuals""].extract(""species"")
    assert fresh_db[""species""].schema == (
        ""CREATE TABLE [species] (\n""
        ""   [id] INTEGER PRIMARY KEY,\n""
        ""   [species] TEXT\n""
        "")""
    )
    assert fresh_db[""individuals""].schema == (
        'CREATE TABLE ""individuals"" (\n'
        ""   [id] INTEGER PRIMARY KEY,\n""
        ""   [name] TEXT,\n""
        ""   [species_id] INTEGER,\n""
        ""   FOREIGN KEY(species_id) REFERENCES species(id)\n""
        "")""
    )
    assert list(fresh_db[""species""].rows) == [
        {""id"": 1, ""species"": ""Wolf""},
        {""id"": 2, ""species"": ""Fox""},
    ]
    assert list(fresh_db[""individuals""].rows) == [
        {""id"": 10, ""name"": ""Terriana"", ""species_id"": 2},
        {""id"": 11, ""name"": ""Spenidorm"", ""species_id"": None},
        {""id"": 12, ""name"": ""Grantheim"", ""species_id"": 1},
        {""id"": 13, ""name"": ""Turnutopia"", ""species_id"": None},
        {""id"": 14, ""name"": ""Wargal"", ""species_id"": 1},
    ]
```","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",722816436,
https://github.com/simonw/sqlite-utils/issues/186#issuecomment-897588624,https://api.github.com/repos/simonw/sqlite-utils/issues/186,897588624,IC_kwDOCGYnMM41gB2Q,9308268,2021-08-12T12:13:25Z,2021-08-12T12:13:25Z,NONE,"I think I ran into an issue that's perhaps related with `extract()`

I have a case where I want to create a lookup table for all the related title data where there are possibly multiple null values in the related columns ....
```python3
sql = """"""\
INSERT INTO ""circulation_info"" (""item_id"", ""bib_title"", ""bib_creator"", ""bib_format"", ""bib_pub_year"", ""checkout_date"")
VALUES
(1, ""title one"", ""creator one"", ""Book"", 2018, ""2021-08-12 00:01""),
(2, ""title two"", ""creator one"", ""Book"", 2019, ""2021-08-12 00:02""),
(3, ""title three"", NULL, ""DVD"", 2020, ""2021-08-12 00:03""),
(4, ""title four"", NULL, ""DVD"", NULL, ""2021-08-12 00:04""),
(5, ""title five"", NULL, ""DVD"", NULL, ""2021-08-12 00:05"")
""""""

with sqlite3.connect('test_bib.db') as con:
    con.execute(sql)
```

when I run the `extract()` method ... 

```python3
db[""circulation_info""].extract(
    [
        ""bib_title"",
        ""bib_creator"",
        ""bib_format""        
    ],
    table=""bib_info"", 
    fk_column=""bib_info_id""
)

db = sqlite_utils.Database(""test_bib.db"")

for row in db[""circulation_info""].rows:
    print(row)

print(""\n---\n"")

for row in db[""bib_info""].rows:
    print(row)
```

results in this .. 
```
{'id': 1, 'item_id': 1, 'bib_info_id': 1, 'bib_pub_year': 2018, 'checkout_date': '2021-08-12 00:01'}
{'id': 2, 'item_id': 2, 'bib_info_id': 2, 'bib_pub_year': 2019, 'checkout_date': '2021-08-12 00:02'}
{'id': 3, 'item_id': 3, 'bib_info_id': None, 'bib_pub_year': 2020, 'checkout_date': '2021-08-12 00:03'}
{'id': 4, 'item_id': 4, 'bib_info_id': None, 'bib_pub_year': None, 'checkout_date': '2021-08-12 00:04'}
{'id': 5, 'item_id': 5, 'bib_info_id': None, 'bib_pub_year': None, 'checkout_date': '2021-08-12 00:05'}

---

{'id': 1, 'bib_title': 'title one', 'bib_creator': 'creator one', 'bib_format': 'Book'}
{'id': 2, 'bib_title': 'title two', 'bib_creator': 'creator one', 'bib_format': 'Book'}
{'id': 3, 'bib_title': 'title three', 'bib_creator': None, 'bib_format': 'DVD'}
{'id': 4, 'bib_title': 'title four', 'bib_creator': None, 'bib_format': 'DVD'}
{'id': 5, 'bib_title': 'title five', 'bib_creator': None, 'bib_format': 'DVD'}
```

Seems like it's correctly generating the row data for those lookups, but it's not correctly updating the foreign key back to the primary table? Looks like it just results in a `NULL` value in that original table.

Any ideas on why? Thanks again!","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",722816436,
https://github.com/simonw/sqlite-utils/issues/186#issuecomment-897600677,https://api.github.com/repos/simonw/sqlite-utils/issues/186,897600677,IC_kwDOCGYnMM41gEyl,9308268,2021-08-12T12:32:14Z,2021-08-12T12:32:14Z,NONE,"Actually, I forgot to include the `bib_pub_year` in the extract ... 

But also, I tried again with empty string values instead of `NULL` values and it seems to place the foreign key properly / correctly... 

```python3
sql = """"""\
INSERT INTO ""circulation_info"" (""item_id"", ""bib_title"", ""bib_creator"", ""bib_format"", ""bib_pub_year"", ""checkout_date"")
VALUES
(1, ""title one"", ""creator one"", ""Book"", 2018, ""2021-08-12 00:01""),
(2, ""title two"", ""creator one"", ""Book"", 2019, ""2021-08-12 00:02""),
(3, ""title three"", """", ""DVD"", 2020, ""2021-08-12 00:03""),
(4, ""title four"", """", ""DVD"", """", ""2021-08-12 00:04""),
(5, ""title five"", """", ""DVD"", """", ""2021-08-12 00:05"")
""""""

with sqlite3.connect('test_bib_2.db') as con:
    con.execute(sql)
```

```python3
db[""circulation_info""].extract(
    [
        ""bib_title"",
        ""bib_creator"",
        ""bib_format"",
        ""bib_pub_year""
    ],
    table=""bib_info"", 
    fk_column=""bib_info_id""
)
```

```
{'id': 1, 'item_id': 1, 'bib_info_id': 1, 'bib_pub_year': 2018, 'checkout_date': '2021-08-12 00:01'}
{'id': 2, 'item_id': 2, 'bib_info_id': 2, 'bib_pub_year': 2019, 'checkout_date': '2021-08-12 00:02'}
{'id': 3, 'item_id': 3, 'bib_info_id': 3, 'bib_pub_year': 2020, 'checkout_date': '2021-08-12 00:03'}
{'id': 4, 'item_id': 4, 'bib_info_id': 4, 'bib_pub_year': '', 'checkout_date': '2021-08-12 00:04'}
{'id': 5, 'item_id': 5, 'bib_info_id': 5, 'bib_pub_year': '', 'checkout_date': '2021-08-12 00:05'}

---

{'id': 1, 'bib_title': 'title one', 'bib_creator': 'creator one', 'bib_format': 'Book'}
{'id': 2, 'bib_title': 'title two', 'bib_creator': 'creator one', 'bib_format': 'Book'}
{'id': 3, 'bib_title': 'title three', 'bib_creator': '', 'bib_format': 'DVD'}
{'id': 4, 'bib_title': 'title four', 'bib_creator': '', 'bib_format': 'DVD'}
{'id': 5, 'bib_title': 'title five', 'bib_creator': '', 'bib_format': 'DVD'}
```
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",722816436,