Summarize data in a new table - mysql

Question

The problem is as follows during the day data is put into status_table (this can reach up to 4000 entries a day
During the night i want to put the data in a more organized way in a storage table
(status_table_storage) and remove it from the status_table.
The idea is to group all the entries that have the same status until the status/error changes. from that point on a new group should start an be placed into the table. an example can be found in the fiddle
what is the best way to do this.
an example of the table structure can be found here: http://sqlfiddle.com/#!9/488524/1

Answer 1

Step by step explanation:
First you order the table by name and timestamp and initialize three user-defined variables.
SELECT s.* FROM status_table s
, (SELECT #group_number := 0, #prevName := NULL, #prevStatus := NULL) var_init_subquery
ORDER BY name, timestamp
As you can see, we can use a subquery for that. The ORDER BY is important, because there's no order in a relational database, unless you specify it.
Now, MySQL evaluates the SELECT clause in the specified order, therefore don't change the order here.
SELECT
s.*,
#prevName,
#prevStatus,
#prevName := s.name,
#prevStatus := s.status
FROM status_table s
, (SELECT #group_number := 0, #prevName := NULL, #prevStatus := NULL) var_init_subquery
ORDER BY name, timestamp
When you execute this statement, you can see, that when we simply select the variables they hold the value of the previous row or NULL when it's the first row, that was read. Then the value of the current row is assigned to the variables. So we can compare now the current row with the previous row. If something changed, we simply increment the third variable, which is a number for each "group" that we are building.
SELECT
s.*,
#group_number := IF(#prevName != s.name OR #prevStatus != s.status, #group_number + 1, #group_number) AS group_number,
#prevName := s.name,
#prevStatus := s.status
FROM status_table s
, (SELECT #group_number := 0, #prevName := NULL, #prevStatus := NULL) var_init_subquery
ORDER BY name, timestamp
So we incremented the #group_number when something changed and assigned the variable to itself if not, so that it doesn't change.
Now we can simply use this query as subquery and do a simple grouping.
SELECT
group_number AS id,
name,
status,
MIN(error) AS error,
MIN(timestamp) AS firstEntry,
MAX(timestamp) AS lastEntry,
COUNT(*) AS entries
FROM (
SELECT
s.*,
#group_number := IF(#prevName != s.name OR #prevStatus != s.status, #group_number + 1, #group_number) AS group_number,
#prevName := s.name,
#prevStatus := s.status
FROM status_table s
, (SELECT #group_number := 0, #prevName := NULL, #prevStatus := NULL) var_init_subquery
ORDER BY name, timestamp
) sq
GROUP BY
group_number,
name,
status
see it working in this sqlfiddle