chore(sqla): assert query does not exceed 1 statement

[villebro]

SUMMARY

Raise understandable error if query consists of multiple statements.

AFTER

For DML queries:

For multiple statements:

BEFORE

For DML queries:

For multiple statements:

TEST PLAN

CI + new test

ADDITIONAL INFORMATION

• Has associated issue:
• Changes UI
• Requires DB Migration.
• Confirm DB Migration upgrade and downgrade tested.
• Introduces new feature or API
• Removes existing feature or API

[codecov-io]

Codecov Report

Merging #11236 into master will decrease coverage by 4.17%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #11236      +/-   ##
==========================================
- Coverage   65.51%   61.34%   -4.18%     
==========================================
  Files         831      831              
  Lines       39303    39302       -1     
  Branches     3592     3592              
==========================================
- Hits        25751    24108    -1643     
- Misses      13443    15013    +1570     
- Partials      109      181      +72     

Flag	Coverage Δ
#cypress	?
#javascript	62.40% <ø> (ø)
#python	60.70% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
superset/connectors/sqla/models.py	89.86% <100.00%> (+0.02%)	⬆️
superset-frontend/src/SqlLab/App.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/explore/App.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/dashboard/App.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/explore/index.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/dashboard/index.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/setup/setupColors.js	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/chart/ChartContainer.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/setup/setupFormatters.js	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/explore/reducers/index.js	0.00% <0.00%> (-100.00%)	⬇️
... and 166 more

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[michellethomas]

@villebro It looks like the error Virtual dataset query must be read-only is sometimes throwing when a query is actually readonly. Someone reported a query that included a WITH statement as having this error. The query is just a select query so I'm guessing that the WITH is getting misinterpreted as not read-only (but I haven't looked into it too much).

The query structure is something like

WITH data AS (
select column_1 from db.table_name
),
SELECT sum(column_1) AS total
FROM data