Select 1 row from table one and then n number of row from other table and go back to first table and select row 2 and so on

Question

I have this SQL script:

CREATE TABLE `table_1` (
  `IDTable_1` int(11) NOT NULL,
  PRIMARY KEY (`IDTable_1`)
);

CREATE TABLE `table_2` (
  `IDTable_2` int(11) NOT NULL,
  `FK_Table_1` int(11) NOT NULL,
  PRIMARY KEY (`IDTable_2`,`FK_Table_1`),
  KEY `FK_Table_1` (`FK_Table_1`)
);

INSERT INTO `table_1` (`IDTable_1`) VALUES
(1),
(2),
(3);

INSERT INTO `table_2` (`IDTable_2`, `FK_Table_1`) VALUES
(1, 1),
(1, 2),
(2, 1),
(2, 3);

What I want is to create a query to get the data like this:

1 row from table_1

n numbers of rows where IDTable_1 appears

Following row from table_1

n numbers of rows where following IDTable_1 appears

And so on.

Example of expected result using the data from script provided:

/*ID 1 from table_1*/
1

/*IDs from table_2 Where ID 1 from table_1 appears*/
1
2

/*ID 2 from table_1*/
2

/*IDs from table_2 Where ID 2 from table_1 appears*/
1

/*ID 3 from table_1*/
3

/*IDs from table_2 Where ID 3 from table_1 appears*/
2

But I have no Idea How to achieve this. Any ideas would be really appreciated.

Answer 1

We can do this using a union query with a computed column:

SELECT id
FROM
(
    SELECT IDTable_1 AS id, IDTable_1 AS pos1, 1 AS pos2 FROM table_1
    UNION ALL
    SELECT IDTable_2, FK_Table_1, 2 FROM table_2
) t
ORDER BY
    pos1,
    pos2;

Note that a two-level sort is required here. The first level, pos1 , places all records from the same IDTable_1 group together. Then, within each of those groups, the pos2 levels places the record from the first table before the record(s) of the second table.

Answer 2

Your question is unclear. See which of these work for you:

-- close to your output, but formatted differently:
SELECT t2.IDTable_1         AS "Id of table_1",
       GROUP_CONCAT(t2.id)  AS "Ids of table_2"
    FROM table_2
    GROUP BY IDTable_1;

-- Count number of rows:
SELECT IDTable_1, COUNT(*)
    FROM table_2
    GROUP BY IDTable_1;

-- contents of both tables:
SELECT t1.*, t2.*
    FROM table_1 AS t1
    JOIN table_2 AS t2  ON t2.IDTable_1 = t1.id;