[GitHub] [arrow] jduo commented on a change in pull request #11982: ARROW-15313: [C++][Java][FlightRPC] Implement type info method to flight-sql

[GitBox <gi...@apache.org>]

jduo commented on a change in pull request #11982:
URL: https://github.com/apache/arrow/pull/11982#discussion_r785652694



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File path: format/FlightSql.proto
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@@ -867,6 +867,69 @@ enum SqlSupportsConvert {
   SQL_CONVERT_VARCHAR = 19;
 }
 
+/*
+ * Represents a request to retrieve information about data type supported ona Flight SQL enabled backend.
+ * Used in the command member of FlightDescriptor for the following RPC calls:
+ *  - GetSchema: return the schema of the query.
+ *  - GetFlightInfo: execute the catalog metadata request.
+ *
+ * The returned schema will be:
+ * <
+ *   type_name: utf8 not null (The name of the data type, for example: VARCHAR, INTEGER, etc),
+ *   data_type: int not null (The SQL data type),
+ *   column_size: int (The maximum column size that the server supports for this data type.
+ *                     For numeric data, this is the maximum precision.
+ *                     For string data, this is the length in characters.
+ *                     For datetime data types, this is the length in characters of the string representation.
+ *                     NULL is returned for data types where column size is not applicable.),
+ *   literal_prefix: utf8 (Character or characters used to prefix a literal, NULL is returned for
+ *                         data types where a literal prefix is not applicable.),
+ *   literal_suffix: utf8 (Character or characters used to terminate a literal,
+ *                         NULL is returned for data types where a literal suffix is not applicable.),
+ *   create_params: utf8 (A list of keywords, separated by commas, corresponding
+ *                        to each parameter that the application may specify in parentheses
+ *                        when using the name that is returned in the TYPE_NAME field.
+ *                        NULL is returned if there are no parameters for the data type definition.),
+ *   nullable: int not null (Shows if the data type accepts a NULL value),
+ *   case_sensitive: bool not null (Shows if a character data type is case-sensitive in collations and comparisons),
+ *   searchable: int not null (Shows how the data type is used in a WHERE clause),
+ *   unsigned_attribute: bool (Shows if the data type is unsigned. NULL is returned if the attribute is
+ *                             not applicable to the data type or the data type is not numeric.),
+ *   fixed_prec_scale: bool not null (Shows if the data type has predefined fixed precision and scale.),
+ *   auto_increment: bool (Shows if the data type is auto incremental. NULL is returned if the attribute
+ *                         is not applicable to the data type or the data type is not numeric.),
+ *   local_type_name: utf8 (Localized version of the data source-dependent name of the data type. NULL
+ *                          is returned if a localized name is not supported by the data source),
+ *   minimum_scale: int (The minimum scale of the data type on the data source.
+ *                       If a data type has a fixed scale, the MINIMUM_SCALE and MAXIMUM_SCALE
+ *                       columns both contain this value. NULL is returned if scale is not applicable.),
+ *   maximum_scale: int (The maximum scale of the data type on the data source.
+ *                       NULL is returned if scale is not applicable.),
+ *   sql_data_type: int not null (The value of the SQL data type as it appears in the

Review comment:
       This field represents the SQL type for most types. The exceptions are datetime and and interval types, where this holds the generic SQL_DATETIME or SQL_INTERVAL type. It's an indication to the user that they can get a more specific subtype of these by using the sql_datetime_sub field.




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