Virtual layers SQL output fields without alias raise errors

[qgib]

Author Name: Giovanni Allegri (@giohappy)
Original Redmine Issue: 16419
Affected QGIS version: master
Redmine category:db_manager

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Calculated fields inside Virtual Layers SQL queries (through DB Manager) must have an alias otherwise it raises errors.
The problem is that it can't be deduced from the error message.

As an example:
@
SELECT
ST_Area("landcover"."geometry")
FROM "landcover"@

will raise the message "Query preparation error on SELECT "ST_Area("comuni"."geometry")" FROM _tview LIMIT 1: near ""."": syntax error"

(you can see it in the vlayer.png image attachment)

The query works fine if an alias is added:

@select
ST_Area("landcover"."geometry") AS area
FROM "landcover"@

I guess that the fix could be to use the field function as a string and use it for the output field name (as DBs do)

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• vlayer.png (Giovanni Allegri)

[qgib]

Author Name: Giovanni Manghi (@gioman)

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• easy_fix was configured as 0
• regression was configured as 0

[qgib]

Author Name: Giovanni Manghi (@gioman)

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Please check if this issue is still valid on QGIS 3.4.5 or 3.6.

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• status_id was changed from Open to Feedback

[gioman]

Does not seems to be an issue anymore.