MySQL如何在最大和最小之间选择一个日期记录

Question

Say I have four dates, for example:

• 1/1/2018
• 2/5/2018
• 4/8/2018
• 9/9/2018

I want to 'select' a date in between the min and max. Either the 2/5/2018 record or the 4/8/2018 record ONLY.

I think I'm close, but this query returns ALL the rows:

SELECT * FROM RUBERIC R  
WHERE R.SCHOOLID = 75 
AND R.TEACHERID = 610 
AND R.OBSERVED = 'Observed Classroom' 
AND R.DATE BETWEEN 
(SELECT MIN(DATE) FROM RUBERIC WHERE R.SCHOOLID = 75 
AND R.TEACHERID = 610 AND R.OBSERVED = 'Observed Classroom' )
AND
(SELECT MAX(DATE) FROM RUBERIC WHERE R.SCHOOLID = 75 
AND R.TEACHERID = 610 AND R.OBSERVED = 'Observed Classroom' )

Answer 1

BETWEEN includes the end points. Presumably, you want to exclude them:

SELECT R.*
FROM RUBERIC R  
WHERE R.SCHOOLID = 75 AND
      R.OBSERVED = 'Observed Classroom' AND
      R.DATE > (SELECT MIN(R2.DATE) FROM RUBERIC R2 WHERE R2.SCHOOLID = 75 
AND R2.TEACHERID = 610 AND R2.OBSERVED = 'Observed Classroom'
               ) AND
      R.DATE < (SELECT MAX(R2.DATE) FROM RUBERIC R2 WHERE R2.SCHOOLID = 75 
AND R2.TEACHERID = 610 AND R2.OBSERVED = 'Observed Classroom'
               );

Also, your query is -- inadvertently -- a correlated subquery. The table alias R refers to the rows in the main query, not the subquery. You should always define table aliases and always use them, but use them properly. (Note all the R2 s in the subqueries in this version.)

In general, I strongly discourage anyone from using BETWEEN with date or date/times. This is not a problem in your case, but the time component can lead to unexpected results.

Answer 2

This is due to the fact that BETWEEN is inclusive. See this answer .

Answer 3

Your BETWEEN condtition doesn't change anything on the result set, since MIN and MAX will be included. You need to split the BETWEEN condition into < and > conditions. But in order to not duplicate the conditions on SCHOOLID, TEACHERID and OBSERVED, I would first select the min and max date in a subquery and then join the table to it.

SELECT R.*
FROM (
    SELECT SCHOOLID, TEACHERID, OBSERVED, MIN(DATE) AS MIN_DATE, MAX(DATE) AS MAX_DATE
    FROM RUBERIC
    WHERE SCHOOLID  = 75 
      AND TEACHERID = 610 
      AND OBSERVED  = 'Observed Classroom'
) X
JOIN RUBERIC R
  ON  R.SCHOOLID  = X.SCHOOLID
  AND R.TEACHERID = X.TEACHERID
  AND R.OBSERVED  = X.OBSERVED
  AND R.DATE      > X.MIN_DATE
  AND R.DATE      < X.MAX_DATE

If you need to select "any" one of the rows, just add LIMIT 1 at the end of the query.