Odbc AstVisitor Custom Connector

Hi zua ,
Based on your description, first, AstVisitor contains one or more rewritten records for controlling SQL query generation. The most common use of this field is to provide logic to generate LIMIT/OFFSET clauses for drivers that do not support TOP. This property can be overridden to append or modify parts of the SQL statement.
To accomplish this, you can define a function and then call it in the join section. You can try this sample:

let
    MyAstVisitor = (ast) =>
        let
            // Modify the AST here
            modifiedAst = ast & " ADDITIONAL SQL STATEMENT"
        in
            modifiedAst,
    Source = Odbc.DataSource("YourConnectionString", [AstVisitor = MyAstVisitor])
in
    Source

To apply the function to a table or SQL statement, it is usually included in the option record when it is called. This ensures that any SQL generated by Power Query will be handled by the custom function.

You can also check out these documents for more information
Parameters for the Odbc.DataSource function - Power Query | Microsoft Learn

Enabling DirectQuery for an ODBC-based Power Query connector - Power Query | Microsoft Learn

Power Query ODBC connector - Power Query | Microsoft Learn

Best regards,
Albert He

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