How do I create an alias for a built-in function?

The issue is that an external application makes a query to Vertica with the SQL command COUNT_BIG. Vertica doesn't provide a function called COUNT_BIG as it has combined with COUNT. I want to make an alias/synonym called COUNT_BIG which would call the COUNT function. How do I go about this?

We're developing UDx functions in Python. Can I simulate a COUNT-like aggregate function in a UDx?

Tagged:

Answers

  • Bryan_HBryan_H Employee

    You can create an alias using CREATE FUNCTION (SQL) as described at https://www.vertica.com/docs/9.3.x/HTML/Content/Authoring/SQLReferenceManual/Statements/CREATEFUNCTIONSQLFunctions.htm
    You could probably write a UDTF in Python to emulate COUNT_BIG, but the above will emulate COUNT_BIG more simply if you don't need further calculations.

  • @Bryan_H said:
    You can create an alias using CREATE FUNCTION (SQL) as described at https://www.vertica.com/docs/9.3.x/HTML/Content/Authoring/SQLReferenceManual/Statements/CREATEFUNCTIONSQLFunctions.htm
    You could probably write a UDTF in Python to emulate COUNT_BIG, but the above will emulate COUNT_BIG more simply if you don't need further calculations.

    I tried something like:
    CREATE FUNCTION
    COUNT_BIG
    RETURN BIGINT
    AS
    BEGIN
    RETURN COUNT;
    END;
    This is obviously not correct, but how do I know what datatype/arguments the COUNT function should receive? I tried something similar and got an error saying something like "return should be simple".

  • Bryan_HBryan_H Employee

    OK, I stand corrected: CREATE FUNCTION (SQL) doesn't operate as a macro, and thus can't parse COUNT as this is non-scalar. So you could write a COUNT_BIG UDTF in Python, or if you have a support contract, you could request a new feature to add a COUNT_BIG macro to be added to the Vertica engine - this would be fairly trivial since INTEGER and BIGINT are the same data type in Vertica (64-bit integer), so COUNT_BIG would just be an alias or macro on COUNT.

  • LenoyJLenoyJ Employee
    edited June 26

    Probably use Directed Queries? Maybe a little wonky and you'll have to do if for every type of query coming in from your tool.
    Something like:

    --Create a pseudo sql function. We'll need this else the next statement will return an error.
    CREATE FUNCTION count_big(x INT) RETURN INT
    AS BEGIN 
     RETURN (x); 
    END;
    
    --Create Directed query
    SAVE QUERY SELECT count_big(1) AS count FROM iris;
    CREATE DIRECTED QUERY CUSTOM 'redirect_countbig_to_count' SELECT count(1) AS count FROM iris;
    ACTIVATE DIRECTED QUERY redirect_countbig_to_count;
    

    Check if it works:

    dbadmin=> SELECT count_big(1) AS count FROM iris;
     count
    -------
       150
    (1 row)
    

    More Info: https://www.vertica.com/docs/10.0.x/HTML/Content/Authoring/AdministratorsGuide/QueryManagement/DirectedQueries/CustomDirectedQueries.htm

Leave a Comment

BoldItalicStrikethroughOrdered listUnordered list
Emoji
Image
Align leftAlign centerAlign rightToggle HTML viewToggle full pageToggle lights
Drop image/file

Can't find what you're looking for? Search the Vertica Documentation, Knowledge Base, or Blog for more information.