Hur man slår samman 2 eller fler datumintervall till 1

Här kommer en lösning som använder användarvariabler. Verifierad med data du angav och jag infogade mer data för verifiering.

För att spara frågeresultatet permanent och hålla det tillgängligt senare skrivs resultatet in i en tabell tbl_new.

Fullständig demo>>

SQL:

-- data preparation
create table tbl(acct varchar(100), start_date date, end_date date);
insert into tbl values
('Acct-1', '2016-01-01', '2016-01-07'),
('Acct-1', '2016-01-05', '2016-01-11'),
('Acct-1', '2016-01-18', '2016-01-24'),
('Acct-1', '2016-02-02', '2016-02-08'),
('Acct-1', '2016-02-07', '2016-02-13'),
('Acct-2', '2016-01-01', '2016-01-07'),
('Acct-2', '2016-01-18', '2016-01-24'),
('Acct-2', '2016-01-02', '2016-02-08');


SELECT * FROM tbl;

-- Need queries
SET @last_acct = '', @last_start_date = '1970-01-01', @last_end_date = '9999-12-31', @group = 1;

CREATE TABLE tbl_new (acct varchar(100), start_date date, end_date date);

INSERT INTO tbl_new 
SELECT 
    acct,
    MIN(start_date) start_date,
    MAX(end_date) end_date
FROM
(
    SELECT
        acct, 
        start_date, 
        end_date,
        CASE 
            WHEN 
                acct = @last_acct AND start_date <= @last_end_date 
            THEN 
                @group
            ELSE
                @group := @group + 1
        END group_num, 
        @last_acct := acct,
        @last_start_date := start_date,
        @last_end_date := end_date
    FROM
        tbl
) tbl2
GROUP BY group_num;

SELECT * FROM tbl_new;

Utdata:

mysql> SELECT * FROM tbl;
+--------+------------+------------+
| acct   | start_date | end_date   |
+--------+------------+------------+
| Acct-1 | 2016-01-01 | 2016-01-07 |
| Acct-1 | 2016-01-05 | 2016-01-11 |
| Acct-1 | 2016-01-18 | 2016-01-24 |
| Acct-1 | 2016-02-02 | 2016-02-08 |
| Acct-1 | 2016-02-07 | 2016-02-13 |
| Acct-2 | 2016-01-01 | 2016-01-07 |
| Acct-2 | 2016-01-18 | 2016-01-24 |
| Acct-2 | 2016-01-02 | 2016-02-08 |
+--------+------------+------------+
8 rows in set (0.00 sec)

mysql>
mysql> -- Need queries
mysql> SET @last_acct = '', @last_start_date = '1970-01-01', @last_end_date = '9999-12-31', @group = 1;
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql> CREATE TABLE tbl_new (acct varchar(100), start_date date, end_date date);
Query OK, 0 rows affected (0.01 sec)

mysql>
mysql> INSERT INTO tbl_new
    -> SELECT
    ->     acct,
    ->     MIN(start_date) start_date,
    ->     MAX(end_date) end_date
    -> FROM
    -> (
    ->     SELECT
    ->         acct,
    ->         start_date,
    ->         end_date,
    ->         CASE
    ->             WHEN
    ->                 acct = @last_acct AND start_date <= @last_end_date
    ->             THEN
    ->                 @group
    ->             ELSE
    ->                 @group := @group + 1
    ->         END group_num,
    ->         @last_acct := acct,
    ->         @last_start_date := start_date,
    ->         @last_end_date := end_date
    ->     FROM
    ->         tbl
    -> ) tbl2
    -> GROUP BY group_num;

Query OK, 5 rows affected (0.00 sec)
Records: 5  Duplicates: 0  Warnings: 0

mysql>
mysql> SELECT * FROM tbl_new;
+--------+------------+------------+
| acct   | start_date | end_date   |
+--------+------------+------------+
| Acct-1 | 2016-01-01 | 2016-01-11 |
| Acct-1 | 2016-01-18 | 2016-01-24 |
| Acct-1 | 2016-02-02 | 2016-02-13 |
| Acct-2 | 2016-01-01 | 2016-01-07 |
| Acct-2 | 2016-01-02 | 2016-02-08 |
+--------+------------+------------+
5 rows in set (0.00 sec)