Azure blob query documentation

What SQL variant is it using? And where can I find its docs and supported features?

To query data stored in blobs, the query_blob function in the Azure Storage client library for Python uses SQL-like syntax. Although the syntax is similar to SQL, it is not a complete SQL implementation.

You can use this MS-DOCS to learn information about the syntax and supported features.

Does it support querying CSV files (or text files in general) line by line? I would like to be able to write a query like select line from file where line contains {search_string}. Does this blob query have that capability?

According to your second question, the query_blob technique does not allow you to query CSV files (or text files in general) line by line. Instead, it allows you to query blob data as a single block of text.

If you want to query CSV data line by line, you must first read the file and then apply your search criteria to each line.

In my environment, I have stored CSV file with data in Azure blob storage like the below:

Here is the below code to read a CSV file line by line and it looks for lines that contain a specified string.

Code:

from azure.storage.blob import BlobServiceClient
import pandas as pd

blob_service_client = BlobServiceClient.from_connection_string("Your-storage-connection-string")
blob_client = blob_service_client.get_blob_client(container="test", blob="sample.csv") 

# Read the csv file line by line and search for lines that contain a specific string
search_string = "44.95"
lines=blob_client.download_blob().content_as_text().splitlines()
for i in range(len(lines)):
    if i==0:
        columns = [lines[i].split(',')]
    else:
        if search_string in lines[i]:
            data = [lines[i].split(',')]
df = pd.DataFrame(data, columns=columns)

print(df)

Output:

                   Title         Author     Genre  Price PublishDate                                  Description
0  XML Developer's Guide  "Gambardella"  Computer  44.95  2000-10-01  "An in-depth look at creating applications