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मॉड्यूल 15 · पाठ 2 का 2पाठ्यक्रम में 57/57~15 min
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JSON एकत्रीकरण कार्य

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.

व्यायाम#sql.m15.l2.e1
प्रयास: 0लोड हो रहा है...

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.

संपादक लोड हो रहा है...
संकेत दिखाएँ

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

3 प्रयासों के बाद समाधान उपलब्ध है

व्यायाम#sql.m15.l2.e2
प्रयास: 0लोड हो रहा है...

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\`.

संपादक लोड हो रहा है...
संकेत दिखाएँ

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

3 प्रयासों के बाद समाधान उपलब्ध है