使用PHP生成随机数据库插入

I have two tables that look like this:

Table: matrix

    matrix_id      round_id    p_1_1     p_1_2     p_2_1     p_2_2     p_3_1     p_3_2
    INT(11)        INT(11)    INT(11)   INT(11)   INT(11)   INT(11)   INT(11)   INT(11)
   AUTOINCREMENT

Table: matrix_elements:

element_id       matrix
 INT(11)         INT(11)
AUTOINCREMENT

Now I need to randomly SELECT from the table matrix_elements and INSERT a new row into the table matrix. Each of those p_1_1, p_1_2 etc.. will have to be filled with the random matrix from the matrix_elements table.

The only requirement is that each two of those columns p_1_1 etc.. will have to be filled with the value: 8

I am totally lost and I did not try anything before you ask. I am just in need of some good directions in order to achieve this, not necessarly a prepared code.

Thanks for any suggestion.

This takes multiple statements to do one row... and I may have misunderstood your requirements, but here goes:

EDIT: Modified to be one statement and actually work with RAND()

INSERT INTO matrix
SELECT
  NULL,
  1, -- NO idea what round_id should be...
  IF( 0 in (one8, two8), 8, (SELECT element_id 
                             FROM matrix_elements ORDER BY RAND() LIMIT 1)),
  IF( 1 in (one8, two8), 8, (SELECT element_id 
                             FROM matrix_elements ORDER BY RAND() LIMIT 1)),
  IF( 2 in (one8, two8), 8, (SELECT element_id 
                             FROM matrix_elements ORDER BY RAND() LIMIT 1)),
  IF( 3 in (one8, two8), 8, (SELECT element_id 
                             FROM matrix_elements ORDER BY RAND() LIMIT 1)),
  IF( 4 in (one8, two8), 8, (SELECT element_id 
                             FROM matrix_elements ORDER BY RAND() LIMIT 1)),
  IF( 5 in (one8, two8), 8, (SELECT element_id 
                             FROM matrix_elements ORDER BY RAND() LIMIT 1))
FROM (
  SELECT
    one8,
    IF( one8 = two8, two8 + 1, two8 ) as two8
    FROM (
      SELECT
        FLOOR(RAND() * 6) AS one8,
        FLOOR(RAND() * 5) AS two8
    ) AS a
) AS b;