I'm starting this issue without a clear reproduction in case someone else has seen this behavior, and to use the issue as a notebook for research.

I'm using Datasette with the SWITRS data set, which is a California Highway Patrol collection of traffic incident data from the past decade or so. I receive data from them in CSV and want to work with it in Datasette, then export it to CSV for mapping in Felt.com.

Their data makes extensive use of codes for incident column data (1 for Monday and so on), some of it integer codes and some of it letter/text codes. The text codes are sometimes blank or -. During import, I'm creating lookup tables for foreign key references to make the Datasette UI presentation of the data easier to read.

If I import the data and set up the integer foreign keys, everything works fine, but if I set up the text foreign keys, CSV export starts to fail.

The foreign key configuration is as follows:

```

Some tables use integer ids, like sensible tables do. Let's import them first

since we favor them.

for TABLE in DAY_OF_WEEK CHP_SHIFT POPULATION SPECIAL_COND BEAT_TYPE COLLISION_SEVERITY do sqlite-utils create-table records.db $TABLE id integer name text --pk=id sqlite-utils insert records.db $TABLE lookup-tables/$TABLE.csv --csv sqlite-utils add-foreign-key records.db collisions $TABLE $TABLE id sqlite-utils create-index records.db collisions $TABLE done

Other tables use letter keys, like they were raised by WOLVES. Let's put them

at the end of the import queue.

for TABLE in WEATHER_1 WEATHER_2 LOCATION_TYPE RAMP_INTERSECTION SIDE_OF_HWY \ PRIMARY_COLL_FACTOR PCF_CODE_OF_VIOL PCF_VIOL_CATEGORY TYPE_OF_COLLISION MVIW \ PED_ACTION ROAD_SURFACE ROAD_COND_1 ROAD_COND_2 LIGHTING CONTROL_DEVICE \ STWD_VEHTYPE_AT_FAULT CHP_VEHTYPE_AT_FAULT PRIMARY_RAMP SECONDARY_RAMP do sqlite-utils create-table records.db $TABLE key text name text --pk=key sqlite-utils insert records.db $TABLE lookup-tables/$TABLE.csv --csv sqlite-utils add-foreign-key records.db collisions $TABLE $TABLE key sqlite-utils create-index records.db collisions $TABLE done ```

You can see the full code and import script here: https://github.com/radical-bike-lobby/switrs-db

If I run this code and then hit the CSV export link in the Datasette interface (the simple link or the "advanced" dialog), export fails after a small number of CSV rows are written. I am not seeing any detailed error messages but this appears in the logging output:

``` INFO: 127.0.0.1:57885 - "GET /records/collisions.csv?_facet=PRIMARY_RD&PRIMARY_RD=ASHBY+AV&_labels=on&_size=max HTTP/1.1" 200 OK Caught this error:

```

(No other output follows error: other than a blank line.)

I've stared at the rows directly after the error occurs and can't yet see what is causing the problem. I'm going to set up a development environment and see if I get any more detailed error output, and then stare more at some problematic lines to see if I can get a simple reproduction.