BigQuery Job Execution details job stages query column names

[devanshmodi]

Hi ,

I am exploring BigQuery Job Information execution details and I am seeing $10 etc in front of column names for different operations like READ, WRITE, etc If we hover on the $230 we get that information from the console, My ask is where get that information that $230 means a particular column name.
Any help will be much appreciated !

[nikacalupas]

Hi devanshmodi,

Welcome to the Google Cloud Community!

It looks like you're exploring an interesting facet of the BigQuery query plan with the $n notation. You are looking for a way to map these $n values back to the original names or expressions, preferably through a programmatic method or clear metadata, rather than depending on the UI hover feature.

Here are a few approaches that may help you identify what each $number represents:

• Navigate to the "Execution Details" tab for your completed query, explore the individual "Stages" (each representing a step in the query), and look for column names within the input/output table schemas for each stage, as well as within the Stage Summary and Operator Details (which provide descriptions of the operations).
• Look closely at the steps leading up to the operation where the $number appears. Trace the data flow back to see where the column was originally introduced or calculated.
• To deduce what each $number represents in your SQL query and execution plan, analyze the GROUP BY clauses, join conditions, calculated columns (AS), and WITH clauses (CTEs). Trace each $number back to its source and infer the column based on the designed SQL logic.

For more information, you may refer to this documentation for more insights. 

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