Alternative values should store in alternative position in array in php - php

Question

When the values fetching from the mysql the values will be stored in series order in the array. But i want the values to store in the array in alternative position. Here some individual values from table
course_id('1') values
Array (
[0] => 15BCA01 [1] => 15BCA02 [2] => 15BCA03 [3] => 15BCA04 [4] => 15BCA05
[5] => 15BCA06 [6] => 15BCA07 [7] => 15BCA08 [8] => 15BCA09 [9] => 15BCA10
[10] => 15BCA11
)
course_id('2') values:
Array (
[0] => 15MCA01 [1] => 15MCA02 [2] => 15MCA03 [3] => 15MCA04 [4] => 15MCA05
)
course_id('3') values:
Array (
[0] => 15MBA01 [1] => 15MBA02 [2] => 15MBA03 [3] => 15MBA04 [4] => 15MBA05
)
course_id('4') values:
Array (
[0] => 15MSC01 [1] => 15MSC02 [2] => 15MSC03
)
course_id('5') values:
Array (
[0] => 15TAM01 [1] => 15TAM02
)
when i execute the mysql command
select register_number from master where master_course_id in('1','2','3','4','5');
Current Output i am getting (as usual in series):
Array (
[0] => 15BCA01 [1] => 15BCA02 [2] => 15BCA03 [3] => 15BCA04 [4] => 15BCA05
[5] => 15BCA06 [6] => 15BCA07 [7] => 15BCA08 [8] => 15BCA09 [9] => 15BCA10
[10] => 15BCA11 [11] => 15MCA01 [12] => 15MCA02 [13] => 15MCA03 [14] => 15MCA04
[15] => 15MCA05 [16] => 15MBA01 [17] => 15MBA02 [18] => 15MBA03 [19] => 15MBA04
[20] => 15MBA05 [21] => 15MSC01 [22] => 15MSC02 [23] => 15MSC03 [24] => 15TAM01
[25] => 15TAM02
)
Desired Output I want(alternative position):
Array (
[0] => 15BCA01 [1] => 15MCA01 [2] => 15BCA02 [3] => 15MCA02 [4] => 15BCA03
[5] => 15MCA03 [6] => 15BCA04 [7] => 15MCA04 [8] => 15BCA05 [9] => 15MCA05
[10] => 15BCA06 [11] => 15MBA01 [12] => 15BCA07 [13] => 15MBA02 [14] => 15BCA08
[15] => 15MBA03 [16] => 15BCA09 [17] => 15MBA04 [18] => 15BCA10 [19] => 15MBA05
[20] => 15BCA11 [21] => 15MSC01 [22] => 15TAM01 [23] => 15MSC02 [24] => 15TAM02
[25] => 15MSC03
)
If the first value in the array from course_id ('1') means the second values should be from course_id ('2') alternatively they should add in array. If the course_id ('1') completed the next course_id('3') should start to add with current course_id ('2'). Like wise all the course_id values should add in the array alternatively. How to achieve this in php

Answer 1

In MySQL you need to use a user-defined variable to add ordering within the master_course_id groups.
SELECT register_number
FROM (
SELECT master_course_id, register_number,
#position := IF(master_course_id = #prev_course, #position+1, 1) AS position,
#prev_course := master_course_id
FROM (SELECT * FROM master
WHERE master_course_id IN ('1', '2', '3', '4', '5')
ORDER BY master_course_id, register_number) AS m,
CROSS JOIN (SELECT #position := 0, #prev_course := null) AS vars
) AS t
ORDER BY position, master_course_id
The subquery adds an extra position column that counts up sequentially within each course ID. Then the outer query reorders everything by position first, then by course ID.