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62 lines
3.7 KiB
Plaintext
62 lines
3.7 KiB
Plaintext
---
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alias: []
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description: 'Documentation for the JSONEachRowWithProgress format'
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input_format: false
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keywords: ['JSONEachRowWithProgress']
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output_format: true
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slug: /interfaces/formats/JSONEachRowWithProgress
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title: 'JSONEachRowWithProgress'
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doc_type: 'reference'
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---
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{/*AUTOGENERATED_START*/}
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| Input | Output | Alias |
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|-------|--------|-------|
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| ✗ | ✔ | |
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## Description {#description}
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Differs from [`JSONEachRow`](/reference/formats/JSON/JSONEachRow)/[`JSONStringsEachRow`](/reference/formats/JSON/JSONStringsEachRow) in that ClickHouse streams each event as a separate JSON object and also yields progress information.
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The related `JSONStringsEachRowWithProgress` format uses the same top-level object kinds; field values are serialized as strings.
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The compact siblings `JSONCompactEachRowWithProgress` and `JSONCompactStringsEachRowWithProgress` share the same stream-object kinds and progress/`LIMIT`/exception caveats; their `row` / `totals` / `min` / `max` payloads are value arrays instead of named objects.
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## Stream objects {#stream-objects}
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Each line of the response is one JSON object. Clients should dispatch on the top-level key:
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| Top-level key | When it appears | Shape |
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|---------------|-----------------|-------|
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| `meta` | Once, before the first `row` (a `progress` object may be emitted before it) | `{"meta":[{"name":...,"type":...}, ...]}` — column names and types |
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| `row` | Once per result row | `{"row":{...}}` — column values for that row |
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| `progress` | Periodically while the query runs | `{"progress":{...}}` — counters such as `read_rows`, `read_bytes`, `total_rows_to_read` |
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| `totals` | When totals are present | `{"totals":{...}}` — totals row values |
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| `min` / `max` | When extremes are present | `{"min":{...}}` / `{"max":{...}}` — extreme row values |
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| `rows_before_limit_at_least` | When the query contains `LIMIT` | `{"rows_before_limit_at_least":N}` — lower estimate of rows there would have been without `LIMIT` (not proof that rows were dropped) |
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| `rows_before_aggregation` | When the query performs aggregation and the `rows_before_aggregation` counter is enabled | `{"rows_before_aggregation":N}` |
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| `exception` | When the query fails, on the HTTP path with `http_write_exception_in_output_format=1` | `{"exception":"..."}` — error text as a **top-level string**, not nested under `row` |
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The `rows_before_limit_at_least` object is emitted when the query contains `LIMIT`, even if the limit did not drop any rows. It is a lower estimate of the number of rows there would have been without `LIMIT` (same meaning as in `JSON`); clients must not treat it as proof that rows were dropped.
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`meta` is emitted once before the first `row`, but a `progress` object can arrive before `meta`. The top-level `exception` object is emitted on the HTTP path only when `http_write_exception_in_output_format=1`; otherwise the error surfaces through the transport. When emitted it is a separate top-level object, not nested under `row`.
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## Example usage {#example-usage}
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```json
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{"meta":[{"name":"num","type":"UInt8"},{"name":"str","type":"String"},{"name":"arr","type":"Array(UInt8)"}]}
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{"row":{"num":42,"str":"hello","arr":[0,1]}}
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{"row":{"num":43,"str":"hello","arr":[0,1,2]}}
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{"row":{"num":44,"str":"hello","arr":[0,1,2,3]}}
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{"progress":{"read_rows":"3","read_bytes":"24","written_rows":"0","written_bytes":"0","total_rows_to_read":"3"}}
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```
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A `progress` object may still be emitted before `meta`. On the HTTP path with `http_write_exception_in_output_format=1`, a failed query ends with a separate top-level object (not nested under `row`):
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```json
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{"exception":"Code: 62. DB::Exception: Syntax error: failed at position 1 (SELECT) (line 1, col 1): ..."}
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```
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## Format settings {#format-settings}
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{/*AUTOGENERATED_END*/}
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