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mysqlcross-join

mysql cross join, but without duplicated pair?

Let's say I have the following row in my table

table rows

id
63
64
65
66
67
68

if I run the following query, I get 30 rows.

SELECT r1.id, r2,id 
  FROM rows AS r1 
    CROSS JOIN rows AS r2 
  WHERE r1.id!=r2.id

result:

63  64
65  64
66  64
67  64
68  64
64  63
65  63
66  63
67  63
68  63
63  65
64  65
66  65
67  65
68  65
63  66
64  66
65  66
67  66
68  66
63  67
64  67
65  67
66  67
68  67
63  68
64  68
65  68
66  68
67  68

how would I get the following result instead of the above?

63,64  
63,65   
63,66
63,67
63,68

64,65
64,66
64,67
64,68

65,66
65,67
65,68

66,67
66,68

67,68

as you see, I don't want to get both 63,64 and 64,63, for example.

Solution

  • Simple, only join with values higher than the current one.

    select r1.id, r2,id 
from rows r1 
cross join rows r2 
where r1.id < r2.id