Metadata Information ==================== With these operations, it is possible to get information on the currently registered tables and their columns. The output format is mostly compatible with the presto format. .. raw:: html
    SHOW SCHEMAS
    SHOW TABLES FROM <schema-name>
    SHOW COLUMNS FROM <table-name>
    DESCRIBE <table-name>
    ANALYZE TABLE <table-name> COMPUTE STATISTICS
        [ FOR ALL COLUMNS | FOR COLUMNS <column>, [ ,... ] ]
    
See :ref:`sql` for information on how to reference schemas and tables correctly. ``SHOW SCHEMAS`` ---------------- Show the schemas registered in ``dask-sql``. Only included for compatibility reasons. There is always just a one called "schema", where all the data is located and an additional schema, called "information_schema", which is needed by some BI tools (which is empty). Example: .. raw:: html
    SHOW SCHEMAS
    
Result: +------------------------+ | Schema | +========================+ | schema | +------------------------+ | information_schema | +------------------------+ ``SHOW TABLES`` --------------- Show the registered tables in a given schema. Example: .. raw:: html
    SHOW TABLES FROM "schema"
    
Result: +------------+ | Table | +============+ | timeseries | +------------+ ``SHOW COLUMNS`` and ``DESCRIBE`` --------------------------------- Show column information on a specific table. Example: .. raw:: html
    SHOW COLUMNS FROM "timeseries"
    
Result: +--------+---------+---------------+ | Column | Type | Extra Comment | +========+=========+===============+ | id | bigint | | +--------+---------+---------------+ | name | varchar | | +--------+---------+---------------+ | x | double | | +--------+---------+---------------+ | y | double | | +--------+---------+---------------+ The column "Extra Comment" is shown for compatibility with presto. ``ANALYZE TABLE`` ----------------- Calculate statistics on a given table (and the given columns or all columns) and return it as a query result. Please note, that this process can be time consuming on large tables. Even though this statement is very similar to the ``ANALYZE TABLE`` statement in e.g. `Apache Spark `_, it does not optimize subsequent queries (as the pendent in Spark will do). Example: .. raw:: html
    ANALYZE TABLE "timeseries" COMPUTE STATISTICS FOR COLUMNS x, y
    
Result: +-----------+-----------+-----------+ | | x | y | +===========+===========+===========+ | count | 30 | 30 | +-----------+-----------+-----------+ | mean | 0.140374 | -0.107481 | +-----------+-----------+-----------+ | std | 0.568248 | 0.573106 | +-----------+-----------+-----------+ | min | -0.795112 | -0.966043 | +-----------+-----------+-----------+ | 25% | -0.379635 | -0.561234 | +-----------+-----------+-----------+ | 50% | 0.0104101 | -0.237795 | +-----------+-----------+-----------+ | 75% | 0.70208 | 0.263459 | +-----------+-----------+-----------+ | max | 0.990747 | 0.947069 | +-----------+-----------+-----------+ | data_type | double | double | +-----------+-----------+-----------+ | col_name | x | y | +-----------+-----------+-----------+