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Modül 15 · Ders 2 ders 2Kurstaki 57/57~15 min
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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, ...) or jsonb_build_object(...)
  • json_agg(...) or jsonb_agg(...)
SQL
SELECT json_build_object('name', first_name, 'city', city) AS data
FROM customers;

You'll see rows printed containing { "name": "...", "city": "..." }, perfectly compliant.

Egzersiz#sql.m15.l2.e1
Denemeler: 0Yükleniyor…

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.

Düzenleyici yükleniyor…
İpucu göster

json_build_object('name', first_name, 'mail', email)

3 denemeden sonra çözüm mevcut

Egzersiz#sql.m15.l2.e2
Denemeler: 0Yükleniyor…

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\`.

Düzenleyici yükleniyor…
İpucu göster

JSON_AGG(product_id) plus a classic group by to gather the data.

3 denemeden sonra çözüm mevcut