Procedures in Bigquery with default parameters

Question

I am creating a procedure in Bigquery to which I want to pass a parameter, in this case the name of a table. But if nothing is passed to the procedure, it will assign a value by default.

This is what I currently have:

CREATE OR REPLACE PROCEDURE `MY_DATASET.MY_PROCEDURE`(tableName STRING)
BEGIN

  DECLARE tableName STRING DEFAULT "MY_TABLE";
  DECLARE queryString STRING;

  SET queryString = SELECT * FROM MY_DATASET.tableName;

END;

This is the error it currently shows me:

Variable 'tableName' previously declared as an argument

If I don't pass any parameters to the procedure, the query is as follows:

SELECT `MY_DATASET.MY_PROCEDURE`();

queryString = SELECT * FROM MY_DATASET.MY_TABLE;

But if I pass a table to the procedure, I need it to create the following query:

SELECT `MY_DATASET.MY_PROCEDURE`('TABLE_TEST');

queryString = SELECT * FROM MY_DATASET.TABLE_TEST;

Answer 1

You may try and consider the below possible workaround.

Since passing a NULL value on a declared parameter will result to expects 1 argument(s), 0 provided error, you may just pass an empty string and then use an IF statement to handle your desired default value if an empty string is passed.

CREATE OR REPLACE PROCEDURE `MY_DATASET.MY_PROCEDURE`(tableName STRING)
BEGIN
DECLARE table_Name STRING;
DECLARE queryString STRING;

SET table_Name = IF (tableName = '', 'MY_TABLE', tableName);

SET queryString = " SELECT * FROM MY_DATASET."||table_Name||"";

SELECT queryString;

END

Output using empty string parameter:

CALL SELECT `MY_DATASET.MY_PROCEDURE`('');

Output using a passed parameter:

CALL `MY_DATASET.MY_PROCEDURE`('TABLE_TEST');