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70 lines
3.5 KiB
Markdown
70 lines
3.5 KiB
Markdown
---
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slug: /en/operations/system-tables/schema_inference_cache
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---
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# Schema inference cache
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Contains information about all cached file schemas.
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Columns:
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- `storage` ([String](/docs/en/sql-reference/data-types/string.md)) — Storage name: File, URL, S3 or HDFS.
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- `source` ([String](/docs/en/sql-reference/data-types/string.md)) — File source.
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- `format` ([String](/docs/en/sql-reference/data-types/string.md)) — Format name.
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- `additional_format_info` ([String](/docs/en/sql-reference/data-types/string.md)) - Additional information required to identify the schema. For example, format specific settings.
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- `registration_time` ([DateTime](/docs/en/sql-reference/data-types/datetime.md)) — Timestamp when schema was added in cache.
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- `schema` ([String](/docs/en/sql-reference/data-types/string.md)) - Cached schema.
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**Example**
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Let's say we have a file `data.jsonl` with this content:
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```json
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{"id" : 1, "age" : 25, "name" : "Josh", "hobbies" : ["football", "cooking", "music"]}
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{"id" : 2, "age" : 19, "name" : "Alan", "hobbies" : ["tennis", "art"]}
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{"id" : 3, "age" : 32, "name" : "Lana", "hobbies" : ["fitness", "reading", "shopping"]}
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{"id" : 4, "age" : 47, "name" : "Brayan", "hobbies" : ["movies", "skydiving"]}
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```
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:::tip
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Place `data.jsonl` in the `user_files_path` directory. You can find this by looking
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in your ClickHouse configuration files. The default is:
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```
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<user_files_path>/var/lib/clickhouse/user_files/</user_files_path>
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```
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:::
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Open `clickhouse-client` and run the `DESCRIBE` query:
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```sql
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DESCRIBE file('data.jsonl') SETTINGS input_format_try_infer_integers=0;
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```
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```response
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┌─name────┬─type────────────────────┬─default_type─┬─default_expression─┬─comment─┬─codec_expression─┬─ttl_expression─┐
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│ id │ Nullable(Float64) │ │ │ │ │ │
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│ age │ Nullable(Float64) │ │ │ │ │ │
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│ name │ Nullable(String) │ │ │ │ │ │
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│ hobbies │ Array(Nullable(String)) │ │ │ │ │ │
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└─────────┴─────────────────────────┴──────────────┴────────────────────┴─────────┴──────────────────┴────────────────┘
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```
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Let's see the content of the `system.schema_inference_cache` table:
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```sql
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SELECT *
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FROM system.schema_inference_cache
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FORMAT Vertical
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```
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```response
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Row 1:
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──────
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storage: File
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source: /home/droscigno/user_files/data.jsonl
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format: JSONEachRow
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additional_format_info: schema_inference_hints=, max_rows_to_read_for_schema_inference=25000, schema_inference_make_columns_nullable=true, try_infer_integers=false, try_infer_dates=true, try_infer_datetimes=true, try_infer_numbers_from_strings=true, read_bools_as_numbers=true, try_infer_objects=false
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registration_time: 2022-12-29 17:49:52
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schema: id Nullable(Float64), age Nullable(Float64), name Nullable(String), hobbies Array(Nullable(String))
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```
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**See also**
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- [Automatic schema inference from input data](/docs/en/interfaces/schema-inference.md)
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