Hi,
I have the 'SchoolYearTeachingDays' table with just one column, in
which are dates:
CREATE TABLE SchoolYearTeachingDays (
aDate DATE PRIMARY KEY
UNIQUE
);
I filled it with many dates which are unique. These dates excludes
dates for Sundays and for Saturdays. I have another, the
'TeachingSaturdaysInSchoolYear' table:
CREATE TABLE TeachingSaturdaysInSchoolYear (
id INT PRIMARY KEY
UNIQUE,
aDate DATE,
TimetableForTheDay TEXT
);
This table holds just two dates. These two dates are for two
Saturdays. On these two Saturdays we have to teach students. When I do
the following query on this table, I get these two records:
2018-04-14
2018-05-05
I want to INSERT these two dates from the
'TeachingSaturdaysInSchoolYear' table into 'SchoolYearTeachingDays'
table.
I am trying with this query:
INSERT INTO SchoolYearTeachingDays
SELECT aDate FROM TeachingSaturdaysInSchoolYear
;
but I get this error: Error: UNIQUE constraint failed:
SchoolYearTeachingDays.aDate
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)
It works. But I am not understanding it at all.
I wish to know followings.
How many times want to inserts the SELECT query the one of the date
from the TeachingSaturdaysInSchoolYear table into
SchoolYearTeachingDays table?
That is: the how many times wants select statement to insert one
record from first table into second table?
--
Best, Pali
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