paul-rogers commented on a change in pull request #1953: Add docs for Drill 

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+parent: "SQL Commands"
+date: 2020-01-13
+Starting from Drill 1.17, you can store table metadata (including schema and 
computed statistics) into Drill Metastore.
+This metadata will be used when querying a table for more optimal plan 
+{% include startnote.html %}In Drill 1.17, this feature is supported for 
Parquet tables only and is disabled by default.{% include endnote.html %}
+To enable Drill Metastore usage, the following option `metastore.enabled` 
should be set to `true`, as shown:
+       SET `metastore.enabled` = true;
+Alternatively, you can enable the option in the Drill Web UI at 
+## Syntax
+The ANALYZE TABLE REFRESH METADATA statement supports the following syntax:
+       ANALYZE TABLE [table_name] [COLUMNS {(col1, col2, ...) | NONE}]
+       REFRESH METADATA ['level' LEVEL]
+       [{COMPUTE | ESTIMATE} | STATISTICS [(column1, column2, ...)]
+       [ SAMPLE number PERCENT ]]
+## Parameters
+The name of the table or directory for which Drill will collect table 
metadata. If the table does not exist, or the table
+ is temporary, the command fails and metadata is not collected and stored.
+*COLUMNS (col1, col2, ...)*
+Optional names of the column(s) for which Drill will generate and store 
metadata. the Stored schema will include all table columns.
+Specifies to ignore collecting and storing metadata for all table columns.
+Optional varchar literal which specifies maximum level depth for collecting 
+Possible values: `TABLE`, `SEGMENT`, `PARTITION`, `FILE`, `ROW_GROUP`, `ALL`. 
Default is `ALL`.
+Generates statistics for the table to be stored into the Metastore.
+If statistics usage is disabled (`planner.enable_statistics` is set to 
`false`), an error will be thrown when this clause is specified.
+Generates estimated statistics for the table to be stored into the Metastore. 
Currently is not supported.
+*(column1, column2, ...)*
+The name of the column(s) for which Drill will generate statistics.
+Optional. Indicates that compute statistics should run on a subset of the data.
+*number PERCENT*  
+An integer that specifies the percentage of data on which to compute 
statistics. For example, if a table has 100 rows, `SAMPLE 50 PERCENT` indicates 
that statistics should be computed on 50 rows. The optimizer selects the rows 
at random. 
+## Related Options
 Review comment:
   Related Session/System Options
   The following options are set via `ALTER SYSTEM SET` or via the Drill Web 
console. Note, because these options affect all users, use `ALTER SYSTEM` to 
set them, not `ALTER SESSION`.

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