SQL query for calling multiple columns with conditions(with NAs)

问题

This is a continuous question from my previous question. I want to write an SQL query calling for several columns with conditions. I'm working on R Studio using RMySQL package. My server is MySQL.

The table looks like this.

organisation          A           B           C           D
Ikea         2018-04-01  2018-05-07  2018-05-09  2018-05-01
Ikea         2018-06-01  2018-05-03  2018-05-29          NA   
Orange       2018-04-02  2018-05-01  2018-07-08  2018-05-26 
Ikea         2018-06-02  2018-05-01          NA  2018-05-26
Nestle       2018-06-02  2018-05-01          NA  2018-05-26
Ikea                 NA  2018-05-05  2018-04-02  2018-06-01

And I want to get a row where the organisation is Ikea, and where the earliest date among four columns (A, B, C, D) is between 2018-05-01 and 2018-05-31.

In a row which contains NA values, I want to ignore the NAs and see what's the earliest date among the rest of the values. For example, for the second row, the earliest date is "2018-05-03"(column B) therefore it meets the criteria.

Therefore only the second the fourth row of the original table above match the conditions. And the result I want to get should be:

organisation          A           B           C           D
Ikea         2018-06-01  2018-05-03  2018-05-29          NA    
Ikea         2018-06-02  2018-05-01          NA  2018-05-26

How should I write an SQL query? Here is my attempt after getting an answer from my previous question, but it doesn't work well for rows with NAs.

SELECT * FROM myTable 
WHERE organisation LIKE Ikea
LEAST(A, B, C, D) >= '2018-05-01' AND
LEAST(A, B, C, D) < '2018-06-01'

Thank you for any kinds of help!

回答1:

Just use coalesce():

SELECT *
FROM myTable 
WHERE organisation LIKE 'Ikea' AND
      LEAST(COALESCE(A, '2019-01-01'), COALESCE(B, '2019-01-01'), COALESCE(C, '2019-01-01'), COALESCE(D, '2019-01-01')) >= '2018-05-01' AND
      LEAST(COALESCE(A, '2019-01-01'), COALESCE(B, '2019-01-01'), COALESCE(C, '2019-01-01'), COALESCE(D, '2019-01-01')) < '2018-06-01';

'2019-01-01' is an arbitrary date after the range.

回答2:

you could try using IFNULL() for the values and use getdate() so if it were null it would just use today and then that wouldnt be considered the least which is basically ignoring them.

like: LEAST(IFNULL(A,getdate()), IFNULL(B,getdate()), IFNULL(C,getdate()), IFNULL(D,getdate()))

hopefully this may push you in the correct direction

unless NA is a string in there which you could use a case statement like case when A = 'NA' THEN getdate() end

could end up looking something like

SELECT * FROM myTable 
WHERE organisation LIKE Ikea
LEAST(IFNULL(A,getdate()), IFNULL(B,getdate()), IFNULL(C,getdate()), IFNULL(D,getdate())) >= '2018-05-01' AND
LEAST(IFNULL(A,getdate()), IFNULL(B,getdate()), IFNULL(C,getdate()), IFNULL(D,getdate())) < '2018-06-01'

SELECT * FROM myTable 
WHERE organisation LIKE Ikea
LEAST(case when A = 'NA' THEN getdate() else A end, case when B = 'NA' THEN getdate() else B end, case when C = 'NA' THEN getdate() else C end, case when D = 'NA' THEN getdate() else D end) >= '2018-05-01' AND
LEAST(case when A = 'NA' THEN getdate() else A end, case when B = 'NA' THEN getdate() else B end, case when C = 'NA' THEN getdate() else C end, case when D = 'NA' THEN getdate() else D end) < '2018-06-01'

回答3:

Consider joining on an aggregate query derived using a UNION ALL:

SELECT m.*
FROM myTable m
INNER JOIN 
   (SELECT t.ID, MIN(t.`DateValue`) As MinDate
    FROM 
       (SELECT ID, organisation, 'A' As 'Category', A As `DateValue` FROM myTable
        UNION ALL
        SELECT ID, organisation, 'B' As 'Category', B As `DateValue` FROM myTable
        UNION ALL
        SELECT ID, organisation, 'C' As 'Category', C As `DateValue` FROM myTable
        UNION ALL
        SELECT ID, organisation, 'D' As 'Category', D As `DateValue` FROM myTable) As t
    WHERE t.organisation = 'Ikea'
    GROUP BY t.ID
    HAVING MIN(t.`DateValue`) >= '2018-05-01' AND MIN(t.`DateValue`) < '2018-06-01') As agg
ON m.ID = agg.ID;

RexTester Demo (Note: dates are in DD-MM-YYYY format)

来源：https://stackoverflow.com/questions/51043189/sql-query-for-calling-multiple-columns-with-conditionswith-nas

标签

mysql

sql

conditional-statements

rmysql