mysql - find the number of occurrences from two columns - mysql

Question

question example :
source | target
apple | dog
dog | cat
door | cat
dog | apple
cat | dog
result :
apple dog 2
dog cat 2
door cat 1
Here is my question, as an example:
I am trying to count the apple and dog occurrence from source and target. The
count is 2, that is; apple dog and dog cat.
In the same way; dog cat and cat dog, they occur 2 times.
How can I do this with mysql ?
the data will be very large, so this is just a simple example.

Answer 1

Assuming Source and Target are joined with an ID I would do this as:
SELECT
FirstValue,
SecondValue,
COUNT(*) As MyCount
FROM
(SELECT
SourceTable.Value FirstValue,
TargetTable.Value SecondValue
FROM
SourceTable
INNER JOIN TargetTable ON SourceTable.IDValue = TargetTable.IDValue
UNION ALL
SELECT
TargetTable.Value FirstValue,
SourceTable.Value SecondValue
FROM
TargetTable
INNER JOIN SourceTable ON TargetTable.IDValue = SourceTable.IDValue)
GROUP BY
FirstValue,
SecondValue
Reading the question again I'm unsure if these are two columns in the same table. If they are then the query can be simplified to:
SELECT
FirstValue,
SecondValue,
COUNT(*) As MyCount
FROM
(SELECT
SourceColumn FirstValue,
TargetColumn SecondValue
FROM
MyTable
UNION ALL
SELECT
TargetColumn FirstValue,
SourceColumn SecondValue
FROM
MyTable)
GROUP BY
FirstValue,
SecondValue

Answer 2

As I see, your issue is: to count your values independent of their order in your columns. So, pair <'foo', 'bar'> should be counted as <'bar', 'foo'>. For that you may use:
SELECT
*,
COUNT(*)
FROM
test
GROUP BY
LEAST(source, target),
GREATEST(source, target)
Note, that:
Mixing non-group columns with group function will work in MySQL only. It's an extension, so server is free to chose any row.

Answer 3

DROP TABLE IF EXISTS my_table;
CREATE TABLE my_table
(source VARCHAR(12) NOT NULL
,target VARCHAR(12) NOT NULL
,PRIMARY KEY(source,target)
);
INSERT INTO my_table VALUES
('apple','dog'),
('dog','cat'),
('door','cat'),
('dog','apple'),
('cat','dog');
SELECT * FROM my_table;
+--------+--------+
| source | target |
+--------+--------+
| apple | dog |
| cat | dog |
| dog | apple |
| dog | cat |
| door | cat |
+--------+--------+
SELECT GREATEST(source,target),LEAST(source,target),COUNT(*) FROM my_table GROUP BY GREATEST(source,target),LEAST(source,target);
+-------------------------+----------------------+----------+
| GREATEST(source,target) | LEAST(source,target) | COUNT(*) |
+-------------------------+----------------------+----------+
| dog | apple | 2 |
| dog | cat | 2 |
| door | cat | 1 |
+-------------------------+----------------------+----------+