Заметки

UPDATE dummy 
SET customer=subquery.customer, 
address=subquery.address, 
partn=subquery.partn 
FROM (SELECT address_id, customer, address, partn FROM /* big hairy SQL */ ...) AS subquery 
WHERE dummy.address_id=subquery.address_id;

UPDATE table T1 
SET column1 = T2.column1 
FROM 
table T2 
INNER JOIN table T3 USING (column2) 
WHERE T1.column2 = T2.column2;

https://stackoverflow.com/questions/6256610/updating-table-rows-in-postgres-using-subquery

Работая с JSON в postgresql заметил следующие момент:

select t.value::uuid
from json_array_elements_text('["e7ded0cd-12dd-47f5-a75b-192376291e83"]'::json) as t;

select (t.value #>> '{id}')::uuid 
from json_array_elements('[{"id": "e7ded0cd-12dd-47f5-a75b-192376291e83"}]'::json) as t;

Две команды возвращают одинаковый результат, но разными способами.

SELECT xact_commit, now(), numbackends FROM pg_stat_database WHERE datname = 'mydb';

• xact_commit — количество транзакций
• numbackends — количество подключений к БД

set enable_seqscan=true