On 6/26/2018 10:42 AM, Csányi Pál wrote:
Igor Tandetnik <i...@tandetnik.org> ezt írta (időpont: 2018. jún. 26.,
K, 16:10):
On 6/26/2018 9:15 AM, Csányi Pál wrote:
Then I get help and this code:
INSERT INTO SchoolYearTeachingDays
SELECT aDate FROM TeachingSaturdaysInSchoolYear T WHERE T.aDate NOT
IN (SELECT S.aDate FROM SchoolYearTeachingDays S)
This says "insert all dates that aren't already present", which of course
avoids UNIQUE constraint.
Just do not understand what are the 'T' and 'S' means out there, after
FROM clause.
Are they CTEs? Are they virtual tables?
They are aliases. You could write TeachingSaturdaysInSchoolYear.aDate in place
of T.aDate without a change in meaning; T.aDate is merely shorter and more
convenient.
--
Igor Tandetnik
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