Update COPY documentation to reflect cahnges (#9754)

docs/source/user-guide/sql/dml.md

@@ -25,11 +25,14 @@ and modifying data in tables.
 ## COPY
 
 Copies the contents of a table or query to file(s). Supported file
-formats are `parquet`, `csv`, and `json` and can be inferred based on
-filename if writing to a single file.
+formats are `parquet`, `csv`, `json`, and `arrow`.
 
 <pre>
-COPY { <i><b>table_name</i></b> | <i><b>query</i></b> } TO '<i><b>file_name</i></b>' [ ( <i><b>option</i></b> [, ... ] ) ]
+COPY { <i><b>table_name</i></b> | <i><b>query</i></b> } 
+TO '<i><b>file_name</i></b>'
+[ STORED AS <i><b>format</i></b> ]
+[ PARTITIONED BY <i><b>column_name</i></b> [, ...] ]
+[ OPTIONS( <i><b>option</i></b> [, ... ] ) ]
 </pre>
 
 For a detailed list of valid OPTIONS, see [Write Options](write_options).
@@ -61,7 +64,7 @@ Copy the contents of `source_table` to multiple directories
 of hive-style partitioned parquet files:
 
 ```sql
-> COPY source_table TO 'dir_name' (FORMAT parquet, partition_by 'column1, column2');
+> COPY source_table TO 'dir_name' STORED AS parquet, PARTITIONED BY (column1, column2);
 +-------+
 | count |
 +-------+
@@ -74,14 +77,20 @@ results (maintaining the order) to a parquet file named
 `output.parquet` with a maximum parquet row group size of 10MB:
 
 ```sql
-> COPY (SELECT * from source ORDER BY time) TO 'output.parquet' (ROW_GROUP_LIMIT_BYTES 10000000);
+> COPY (SELECT * from source ORDER BY time) TO 'output.parquet' OPTIONS (MAX_ROW_GROUP_SIZE 10000000);
 +-------+
 | count |
 +-------+
 | 2     |
 +-------+
 ```
 
+The output format is determined by the first match of the following rules:
+
+1. Value of `STORED AS`
+2. Value of the `OPTION (FORMAT ..)`
+3. Filename extension (e.g. `foo.parquet` implies `PARQUET` format)
+
 ## INSERT
 
 Insert values into a table.