问题
I want to optimize the space of my Big Query and google storage tables. Is there a way to find out easily the cumulative space that each field in a table gets? This is not straightforward in my case, since I have a complicated hierarchy with many repeated records.
回答1:
You can do this in Web UI by simply typing (and not running) below query changing to field of your interest
SELECT <column_name>
FROM YourTable
and looking into Validation Message that consists of respective size
Important - you do not need to run it – just check validation message for bytesProcessed and this will be a size of respective column
Validation is free and invokes so called dry-run
If you need to do such “columns profiling” for many tables or for table with many columns - you can code this with your preferred language using Tables.get API to get table schema ; then loop thru all fields and build respective SELECT statement and finally Dry Run it (within the loop for each column) and get totalBytesProcessed which as you already know is the size of respective column
回答2:
I don't think this is exposed in any of the meta data. However, you may be able to easily get good approximations based on your needs. The number of rows is provided, so for some of the data types, you can directly calculate the size: https://cloud.google.com/bigquery/pricing
For types such as string, you could get the average length by querying e.g. the first 1000 fields, and use this for your storage calculations.
来源：https://stackoverflow.com/questions/39079195/find-out-the-amount-of-space-each-field-takes-in-google-big-query