Export Postgres table as json

Try here for a basic intro to PostgreSQL and JSON.

Also, PostgreSQL documentation is pretty good, so try it here. Check out the pretty_bool option.

Your original question was "Is there a way to export postgres table data as JSON". You wanted it in this format

{'id':1,'name':'David'}
{'id':2,'name':'James'}
...

I didn't have a running instance of PostgreSQL so I downloaded, compiled and installed 9.4.

To answer this, I first CREATEed a table (fred)

CREATE TABLE fred (mary INT, jimmy INT, paulie VARCHAR(20));

INSERT INTO fred VALUES (2,    43, 'asfasfasfd'      );
INSERT INTO fred VALUES (3,   435, 'ererere'         );
INSERT INTO fred VALUES (6, 43343, 'eresdfssfsfasfae');

Then, to check:

test=# select * from fred;

 mary | jimmy |      paulie      
------+-------+------------------
    2 |    43 | asfasfasfd
    3 |   435 | ererere
    6 | 43343 | eresdfssfsfasfae

Then I issued this command

test=# COPY (SELECT ROW_TO_JSON(t) 
test(# FROM (SELECT * FROM fred) t) 
test-# TO '/paulstuff/sware/db/postgres/inst/myfile';
COPY 3
test=# 

I then quit psql and listed the file myfile.

test=# \q
[pol@polhost inst]$ more myfile 
{"mary":2,"jimmy":43,"paulie":"asfasfasfd"}
{"mary":3,"jimmy":435,"paulie":"ererere"}
{"mary":6,"jimmy":43343,"paulie":"eresdfssfsfasfae"}
[pol@polhost inst]$

(you can experiment with the output from

COPY (SELECT ROW_TO_JSON(t, TRUE)  -- <-- Note addition of "TRUE" here!

at your leisure).

It was pointed out by @offby1 that the output (while corresponding to the OP's question) is not correct JSON. @EvanCarroll pointed out that \o is also a way of outputting to a file, so I combined the solutions to these two niggles in this statement (with help from here):

test=# \o out.json
test=# SELECT array_to_json(array_agg(fred), FALSE) AS ok_json FROM fred;
                                     -- <-- "TRUE" here will produce plus
                                        ("+) signs in the output. "FALSE"
                                        is the default anyway.
test=# \o

gives:

[pol@polhost inst]$ more out.json 
                                                                   ok_json                                                                    
----------------------------------------------------------------------------------------------------------------------------------------------
 [{"mary":2,"jimmy":43,"paulie":"asfasfasfd"},{"mary":3,"jimmy":435,"paulie":"ererere"},{"mary":6,"jimmy":43343,"paulie":"eresdfssfsfasfae"}]
(1 row)
[pol@polhost inst]$ 

FINALLY, there is the backslash (\) problem alluded to by @AdamGent in his post. This was a bit tricky, but it is possible without resorting to post-query processing. Voilà:

INSERT INTO fred VALUES (35, 5, 'wrew\sdfsd');
INSERT INTO fred VALUES (3, 44545, '\sdfs\\\sfs\\gf');

And using REGEXP_REPLACE thus (note the cast ::TEXT) removes the excess blackslashes.

test=# \o slash.json
test=# SELECT REGEXP_REPLACE(ROW_TO_JSON(t)::TEXT, '\\\\', '\\', 'g') 
test=# FROM (SELECT * FROM fred) AS t;  -- I found that using a CTE was helpful for legibility
test=# \o
test=# \q

gives:

[pol@polhost inst]$ more slash.json 
                    regexp_replace                    
------------------------------------------------------
 {"mary":2,"jimmy":43,"paulie":"asfasfasfd"}
 {"mary":3,"jimmy":435,"paulie":"ererere"}
 {"mary":6,"jimmy":43343,"paulie":"eresdfssfsfasfae"}
 {"mary":35,"jimmy":5,"paulie":"wrew\sdfsd"}
 {"mary":3,"jimmy":44545,"paulie":"\sdfs\\\sfs\\gf"}
(5 rows)
[pol@polhost inst]$ 

(p.s. As for @Zoltán 's comment - this may be a version thing - unable to reproduce!).

If you're using psql then there is no reason to use \COPY at all.

\t
\a
\o file.json
SELECT row_to_json(r) FROM my_table AS r;

This is the same method we use to get png/jpgs/tifs out of the database with PostGIS for quick tests, and also to generate script files with PostgreSQL extensions.

For me @Vérace's answer didn't maintain the column names, but assigned default names (f1, f2, etc.) instead. I am using PostgreSQL 9.1 with the JSON extension.

If you want to export the entire table, there is no need for a subquery. In addition, this will maintain the column names. I used the folowing query:

COPY (SELECT row_to_json(t) FROM fred as t) to '/home/pol/Downloads/software/postgres/inst/myfile';