topic how to i able to read column mapping metadata for delta tables in Data Engineering

how to i able to read column mapping metadata for delta tables

sher — Tue, 19 Dec 2023 18:28:40 GMT

i want to read column mapping metadata

https://github.com/delta-io/delta/blob/master/PROTOCOL.md#column-mapping

in above link we can able to find the code block with json data. the same data i want to read in pyspark.. is there any option to read that metadata from databricks please let me know

below code block i want to read for my delta tables

{ "name" : "e", "type" : { "type" : "array", "elementType" : { "type" : "struct", "fields" : [ { "name" : "d", "type" : "integer", "nullable" : false, "metadata" : { "delta.columnMapping.id": 5, "delta.columnMapping.physicalName": "col-a7f4159c-53be-4cb0-b81a-f7e5240cfc49" } } ] }, "containsNull" : true }, "nullable" : true, "metadata" : { "delta.columnMapping.id": 4, "delta.columnMapping.physicalName": "col-5f422f40-de70-45b2-88ab-1d5c90e94db1" } }

Re: how to i able to read column mapping metadata for delta tables

brockb — Wed, 20 Dec 2023 23:12:52 GMT

Hi,

Information about the delta table such as history information could be found by running a `describe history table_name`. A `rename column` operation could be found in the `operation` column with a value of `RENAME COLUMN`.

If you then look at the corresponding delta transaction json file in the table's `_delta_log` directory, you will find the details. For example, if the column rename occurred in Delta version 1, you could go to the `<tableLocation>/_delta_log/00000000000000000001.json` file for the details.

You could read this json file with `spark.read.json(path)`. Much of the data of interest to you would be in the `metaData.schemaString` column.

I hope this helps.

Re: how to i able to read column mapping metadata for delta tables

sher — Sun, 14 Jan 2024 07:44:32 GMT

thanks