Beaver's functionality

 The errors you're encountering are due to differences in the SQL functions supported by Oracle and SQL Server. The LEFT and ISNULL functions are specific to SQL Server, and Oracle does not recognize them, which is why you're getting the ORA-00904: "LEFT": invalid identifier error.

Solutions:

Use Oracle-Compatible Functions:

For LEFT, use Oracle's SUBSTR function:

SELECT COLA, SUBSTR(COLB, 1, 10) FROM TABLEA;

For ISNULL, use Oracle's NVL function:

SELECT COLA, NVL(COLB, 'default_value') FROM TABLEA;

Transform Data in SQL Server:

If you can migrate the data without transformations, you can use the SQL Server-specific functions like LEFT and ISNULL after the data has been moved.

DBeaver Script Configuration:

If you want to write cross-platform scripts, you can use DBeaver's functionality to define SQL scripts for each database type, ensuring the correct functions are used for each.

If you need to run these functions as part of the migration process, you'll have to use Oracle-compatible syntax until the data is in SQL Server.