Skip to content

Loading JSON into Postgres

Today I had to load some JSON data into Postgres.

Postgres' COPY command it expects one JSON object per line rather than a full array.

For example, instead of a JSON array:

[
 { "id": 1, "name": "John Conway" },
 { "id": 2, "name": "Richard Feynman" },
]

It needs to be this format:

{ "id": 1, "name": "John Conway" }
{ "id": 2, "name": "Richard Feynman" }

It took me a surprisingly long time to get the data into Postgres, but the solution was fairly simple.

Here's how I did it.

Convert the data

This is done with one command:

cat input.json | jq -cr '.[]' | sed 's/\\[tn]//g' > output.json

Explanation

  1. cat input.json - read the contents of the file
  2. | jq -cr '.[]' - pipe JSON into jq (opens new window) and split it onto every line
  3. | sed 's/\\[tn]//g' - [optional] remove tabs, newlines etc
  4. > output.json - output to a new file

Importing the data

From here it's easiest to ingest the data into a JSONB column.

## Create a table
psql -h localhost -p 5432 postgres -U postgres -c "CREATE TABLE temp (data jsonb);"

## Copy your data in
cat output.json | psql -h localhost -p 5432 postgres -U postgres -c "COPY temp (data) FROM STDIN;"

That's it

20 seconds of reading, and 1 hour of my time. To get the data out of the table now you can use any of Postgres' amazing JSON support. For example:

select data->>'name'
from temp;

-- John Conway
-- Richard Feynman

Enjoy.