My normal query:
SELECT
DISTINCT vt.id as id,
vtt.name as n,
vt.etxid as etx
FROM vt
LEFT JOIN vtt ON
(vtt.locale = "etx"
AND vtt.etxid = vt.etxid)
Execution time: 5ms
My view:
CREATE OR REPLACE VIEW myview AS
SELECT
DISTINCT vt.id as id,
vtt.name as n,
vt.etxid as etx
FROM vt
LEFT JOIN vtt ON
(vtt.locale = "etx"
AND vtt.etxid = vt.etxid)
My view query:
SELECT * from myview;
Execution time: 600ms
As soon as you mention DISTINCT or aggregation functions in a view MySQL selects TEMPTABLE algorithm for this view, and it means it will create a temporary table for the view and then apply sorting, grouping, and aggregations to it. See more details here. Also, there are some recommendations here concerning view performance.