MySQL Query to Subtract 1st column of 1st row with 2nd column of 2nd row

Question

I'm struggling with a Mysql Code, and I have no clue how to solve this. I have two columns with time value on which I've ordered by desc in Mysql Query result.

I need to find out the differences between the 2nd row StateEndTime and the 1st-row StateStarTtime nd so on and display this in a new row/column. The final table should look like this :

ID          Type         StateStarTtime    StateEndTime   Min Difference

xxx         YYY          03:57             03:59          00:02
xxx         ZZZ          03:53             03:55          00:04
xxx         ZZZ          03:46             03:49          

Answer 1

Assuming ID is an auto increment column, this can be achieved in MySQL by self join technique:

 SELECT 
  t1.ID,
  t1.Type,
  t1.StateStartTime,
  t1.StateEndTime
  (t1.StateStartTime - t2.StateEndTime) AS Min_Diff
 FROM
 Table1 t1
    INNER JOIN
 Table1 t2 ON t2.id = t1.id + 1

Answer 2

Is this what you trying to do?

  mysql_query("SELECT *, `StateEndTime`-`StateStarTtime` AS `Min Difference` 
  FROM `TableName`");

Answer 3

This could be simplified in a MYSQL 8 with CTE and or the ROW_NUM function but this will work to get the solution you are after in most versions.

I've also casted your times as in the example they arent in the correct format, this may not be the case in your actual data.

SET @row_number_a = 0;
SET @row_number_b = -1;

SELECT a.id, a.type, a.start, a.end, TIMEDIFF(CAST(a.start AS TIME), CAST(b.end AS TIME)) AS DIFF  
FROM
(SELECT (@row_number_a:=@row_number_a + 1) AS num, id, type, start, end
FROM tbl) a

LEFT JOIN (
SELECT (@row_number_b:=@row_number_b + 1) AS num, id, type, start, end
FROM tbl
) b
ON a.num = b.num

Result:

"id"    "type"  "start" "end"   "DIFF"
"xxx"   "YYY"   "03:57" "03:59" "00:02:00"
"xxx"   "ZZZ"   "03:53" "03:55" "00:04:00"
"xxx"   "ZZZ"   "03:46" "03:49" \N