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UNION + INTO OUTFILE is confusing
If I run this query:
SELECT 1 UNION SELECT 2 INTO OUTFILE 'test.txt';
It creates a file 'test.txt' with this content:
Looks fine so far.
Now if I do "rm test.txt" and execute another query (with parentheses):
(SELECT 1) UNION (SELECT 2 INTO OUTFILE 'test.txt');
it still puts the same two records from both UNION parts!
This looks confusing, as parentheses a kind of assume that only
the right UNION part is to be exported.
Exporting only one UNION part is not supported, IIRC.
So the above query should probably return a syntax error.
But now there is a new trouble. There is no syntax like this:
(SELECT ...) UNION (SELECT ...) INTO OUTFILE 'test.txt';
So instead of:
(SELECT ...) UNION (SELECT ... INTO OUTFILE 'test.txt');
one will have to write this:
SELECT * INTO OUTFILE 'test.txt'
FROM ((SELECT ...) UNION (SELECT ...)) AS t1;
The latter looks longer, but at least it's not confusing as the former.