How to extract this json into a table? - sql

Question

I've a sql column filled with json document, one for row:
[{
"ID":"TOT",
"type":"ABS",
"value":"32.0"
},
{
"ID":"T1",
"type":"ABS",
"value":"9.0"
},
{
"ID":"T2",
"type":"ABS",
"value":"8.0"
},
{
"ID":"T3",
"type":"ABS",
"value":"15.0"
}]
How is it possible to trasform it into tabular form? I tried with redshift json_extract_path_text and JSON_EXTRACT_ARRAY_ELEMENT_TEXT function, also I tried with json_each and json_each_text (on postgres) but didn't get what expected... any suggestions?
desired results should appear like this:
T1 T2 T3 TOT
9.0 8.0 15.0 32.0

Answer 1

I assume you printed 4 rows. In postgresql
SELECT this_column->'ID'
FROM that_table;
will return column with JSON strings. Use ->> if you want text column. More info here: https://www.postgresql.org/docs/current/static/functions-json.html
In case you were using some old Postgresql (before 9.3), this gets harder : )

Answer 2

Your best option is to use COPY from JSON Format. This will load the JSON directly into a normal table format. You then query it as normal data.
However, I suspect that you will need to slightly modify the format of the file by removing the outer [...] square brackets and also the commas between records, eg:
{
"ID": "TOT",
"type": "ABS",
"value": "32.0"
}
{
"ID": "T1",
"type": "ABS",
"value": "9.0"
}
If, however, your data is already loaded and you cannot re-load the data, you could either extract the data into a new table, or add additional columns to the existing table and use an UPDATE command to extract each field into a new column.
Or, very worst case, you can use one of the JSON Functions to access the information in a JSON field, but this is very inefficient for large requests (eg in a WHERE clause).