Modül dersleri (2/2)
JSON toplama işlevleri
JSON Aggregation Functions
The integration is bidirectional. The database doesn't have to limit itself to parsing JSON: it can build it. Imagine if your API and Node.js didn't have to do the dirty, intensive work of serializing nested objects into JSON, because the DB delivered them already built straight from disk.
Building Objects and Arrays
Instead of the classic mass aggregation or string concatenation (String_agg), we turn to these functions:
json_build_object(key, value, ...)orjsonb_build_object(...)json_agg(...)orjsonb_agg(...)
SELECT json_build_object('name', first_name, 'city', city) AS data
FROM customers;You'll see rows printed containing { "name": "...", "city": "..." }, perfectly compliant.
From the 'customers' table, return the data as JSON rows, mapped with \`json_build_object\`. Map two keys: 'name' bound to 'first_name', and 'mail' bound to 'email'. Use \`AS customer_doc\` for the column.
İpucu göster
json_build_object('name', first_name, 'mail', email)
3 denemeden sonra çözüm mevcut
For each order (\`order_id\`), build in a single unit all the \`product_id\`s it includes. From the 'order_items' table, run \`GROUP BY order_id\`. Then select \`order_id\` and accumulate into a JSON array (JSON_AGG) just the \`product_id\` data. Name the array \`products\`.
İpucu göster
JSON_AGG(product_id) plus a classic group by to gather the data.
3 denemeden sonra çözüm mevcut