INFER_SCHEMA (Lakehouse v1)

Automatically detects the file metadata schema and retrieves the column definitions.

Caution

infer_schema currently only supports parquet file format.

SQL Syntax

INFER_SCHEMA(
  LOCATION => '{ internalStage | externalStage }'
  [ PATTERN => '<regex_pattern>']
)

Where:

Internalstage

internalStage ::= @<internal_stage_name>[/<path>]

Externalstage

externalStage ::= @<external_stage_name>[/<path>]

PATTERN = ‘regex_pattern’

A PCRE2-based regular expression pattern string, enclosed in single quotes, specifying the file names to match. see below to see an example. For PCRE2 syntax, see http://www.pcre.org/current/doc/html/pcre2syntax.html.

SQL Examples

Generate a parquet file in a stage:

CREATE STAGE infer_parquet FILE_FORMAT = (TYPE = PARQUET);
COPY INTO @infer_parquet FROM (SELECT * FROM numbers(10)) FILE_FORMAT = (TYPE = PARQUET);

LIST @infer_parquet;
┌───────────────────────────────────────────────────────┬──────┬────────────────────────────────────┬───────────────────────────────┬─────────┐
│ name                                                  │ size │ md5                                │ last_modified                 │ creator │
├───────────────────────────────────────────────────────┼──────┼────────────────────────────────────┼───────────────────────────────┼─────────┤
│ data_e0fd9cba-f45c-4c43-aa07-d6d87d134378_0_0.parquet │  258 │ "7DCC9FFE04EA1F6882AED2CF9640D3D4" │ 2023-02-09 05:21:52.000 +0000 │ NULL    │
└───────────────────────────────────────────────────────┴──────┴────────────────────────────────────┴───────────────────────────────┴─────────┘

infer_schema

SELECT * FROM INFER_SCHEMA(location => '@infer_parquet/data_e0fd9cba-f45c-4c43-aa07-d6d87d134378_0_0.parquet');
┌─────────────┬─────────────────┬──────────┬──────────┐
│ column_name │ type            │ nullable │ order_id │
├─────────────┼─────────────────┼──────────┼──────────┤
│ number      │ BIGINT UNSIGNED │        0 │        0 │
└─────────────┴─────────────────┴──────────┴──────────┘

infer_schema With Pattern Matching

SELECT * FROM infer_schema(location => '@infer_parquet/', pattern => '.*parquet');
┌─────────────┬─────────────────┬──────────┬──────────┐
│ column_name │ type            │ nullable │ order_id │
├─────────────┼─────────────────┼──────────┼──────────┤
│ number      │ BIGINT UNSIGNED │        0 │        0 │
└─────────────┴─────────────────┴──────────┴──────────┘

Create a Table From Parquet File

The infer_schema can only display the schema of a parquet file and cannot create a table from it.

To create a table from a parquet file:

CREATE TABLE mytable AS SELECT * FROM @infer_parquet/ (pattern=>'.*parquet') LIMIT 0;

DESC mytable;
┌────────┬─────────────────┬──────┬─────────┬───────┐
│ Field  │ Type            │ Null │ Default │ Extra │
├────────┼─────────────────┼──────┼─────────┼───────┤
│ number │ BIGINT UNSIGNED │ NO   │ 0       │       │
└────────┴─────────────────┴──────┴─────────┴───────┘