> ## Documentation Index
> Fetch the complete documentation index at: https://docs.zangtable.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Query and indexes
> Use read-only SQL and table indexes.
ZangTable exposes a read-only SQL query endpoint for reporting, lookups, joins, and debugging data relationships. Index endpoints help speed up common filters and sorts, especially when a table starts getting larger.
Use the query endpoint when you want to answer questions like:
* "Which members have overdue library books?"
* "Which customers have open invoices?"
* "Which orders should be merged with shipment rows by `order_id`?"
* "What query shape should I turn into a dedicated app endpoint later?"
The query endpoint is read-only. Use record and schema endpoints for writes.
## Read-only query
```bash theme={null}
curl -X POST "$BASE_URL/projects/$PROJECT/query" \
-H "Authorization: Bearer $ZANGTABLE_TOKEN" \
-H "Content-Type: application/json" \
--data '{"sql":"SELECT id, title FROM books WHERE status = ?","params":["late"]}'
```
Example response:
```json theme={null}
{
"ok": true,
"data": {
"rows": [
{"id": 101, "title": "The Pragmatic Programmer"},
{"id": 102, "title": "Clean Architecture"}
],
"row_count": 2,
"limit": 500,
"duration_ms": 4
},
"error": null
}
```
## Relational example: find members with late library books
First, fetch late loans:
```bash theme={null}
curl -X POST "$BASE_URL/projects/$PROJECT/query" \
-H "Authorization: Bearer $ZANGTABLE_TOKEN" \
-H "Content-Type: application/json" \
--data '{"sql":"SELECT member_id, book_id, due_date FROM loans WHERE returned_at IS NULL AND due_date < ?","params":["2026-06-01"]}'
```
```json theme={null}
{
"ok": true,
"data": {
"rows": [
{"member_id": 7, "book_id": 101, "due_date": "2026-05-20"},
{"member_id": 9, "book_id": 102, "due_date": "2026-05-22"}
],
"row_count": 2
},
"error": null
}
```
Then fetch the matching members:
```bash theme={null}
curl -X POST "$BASE_URL/projects/$PROJECT/query" \
-H "Authorization: Bearer $ZANGTABLE_TOKEN" \
-H "Content-Type: application/json" \
--data '{"sql":"SELECT id, email, name FROM members WHERE id IN (?, ?)","params":[7,9]}'
```
```json theme={null}
{
"ok": true,
"data": {
"rows": [
{"id": 7, "email": "ada@example.com", "name": "Ada"},
{"id": 9, "email": "grace@example.com", "name": "Grace"}
],
"row_count": 2
},
"error": null
}
```
Your backend can merge those results by `member_id` / `id` and send reminder emails to members with late books. Once the pattern is stable, you can also run it as one SQL query with a join:
```sql theme={null}
SELECT members.id, members.email, members.name, loans.book_id, loans.due_date
FROM members
JOIN loans ON loans.member_id = members.id
WHERE loans.returned_at IS NULL AND loans.due_date < ?
```
## Indexes
Use indexes when the same columns power frequent filters, sorts, joins, or dashboard views. For example, if you often query late loans by `returned_at` and `due_date`, create an index on those columns so SQLite can find matching rows faster.