An external table schema defines the columns and data types of the data stored in an external stage. All external tables include the following columns by default:

• VALUE: A VARIANT type column that represents a single row in the external file.
• METADATA$FILENAME: A pseudocolumn that identifies the name of each staged data file included in the external table, including its path in the stage.
• METADATA$FILE_ROW_NUMBER: A pseudocolumn that shows the row number for each record in a staged data file.

You can also create additional virtual columns as expressions using the VALUE column and/or the pseudocolumns. However, the following columns are not valid for external tables and cannot be included in the schema:

• METADATASROW_ID: This column is only available for internal tables and shows the unique identifier for each row in the table.
• METADATASISUPDATE: This column is only available for internal tables and shows whether the row was inserted or updated by a merge operation.
• METADATASEXTERNAL TABLE PARTITION: This column is not a valid column name and does not exist in Snowflake.

References: Introduction to External Tables, CREATE EXTERNAL TABLE

By default, Snowflake does not allow sharing data from a Business Critical edition to a non-Business Critical edition. This is because Business Critical edition provides enhanced security and data protection features that are not available in lower editions. However, this restriction can be overridden by setting the share_restriction parameter on the shared object (database, schema, or table) to false. This parameter allows the data provider to explicitly allow sharing data with lower edition accounts. Note that this parameter can only be set by the data provider, not the data consumer. Also, setting this parameter to false may reduce the level of security and data protection for the shared data.

References:

• Enable Data Share:Business Critical Account to Lower Edition
• Sharing Is Not Allowed From An Account on BUSINESS CRITICAL Edition to an Account On A Lower Edition
• SQL Execution Error: Sharing is Not Allowed from an Account on BUSINESS CRITICAL Edition to an Account on a Lower Edition
• Snowflake Editions | Snowflake Documentation

• Warehouse credits are used to pay for the processing time used by each virtual warehouse in Snowflake. A virtual warehouse is a cluster of compute resources that enables executing queries, loading data, and performing other DML operations. Warehouse credits are charged based on the number of virtual warehouses you use, how long they run, and their size1.
• Among the commands listed in the question, the following ones will use warehouse credits:
• The command that will not use warehouse credits is:

References: : Understanding Compute Cost : MAX Function : COUNT Function : GROUP BY Clause : SHOW TABLES