检查第一个表中的行，将它们与第二个表中的行进行比较并输出匹配项

Question

I made my story shorter, as requested.

I am trying to create a time table for students. I have two tables:

CREATE TABLE IF NOT EXISTS TIMETABLE
(ID INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
YEAR TEXT NOT NULL,
DATE TEXT,
GROUP TEXT,
BEGIN TEXT,
END TEXT,
ROOM TEXT,
SUBJECT TEXT NOT NULL,
TEACHER TEXT,
IN_DATES INT,
TIMESTAMP TIME)

CREATE TABLE IF NOT EXISTS DATES
(ID INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
SUBJECT TEXT NOT NULL,
TEACHER TEXT NOT NULL,
GROUP TEXT,
DATE TEXT,
TIMESTAMP TEXT

The first table has all classes for all faculties (eg for the first year of studies). The second one contains rows with dates of classes that do not take place weekly (that means, eg every 2 weeks or with irregular dates).

In short: If row has IN_DATES = 0 then we can output it directly. If row has IN_DATES = 1 then we need to check if there is a class with the same date and subject in DATES . If there is a match, we output the whole row from TIMETABLE . If there is no match, we do not display this row.

How to write the SQL query to accomplish this?

My English may not be very good as it is not my native language.

Happy new year ;)

Answer 1

SELECT *
FROM Timetable t
WHERE in_dates = 0 OR
  (
    in_dates = 1 AND
    EXISTS (
     SELECT 1
     FROM Dates d
     WHERE d.subject = t.subject AND
       d.date = t.date
    )
  )