MySql split table on insert
You have an AUTO_INCREMENT sql_id, so you have the rows numbered 1,2,3, 4,5,6, ... (unless you are using a clustering or Multi-Master setup that sets auto_increment_increment to something other than 1).

So, load the data into a table, then copy thirds into the three desired tables, and finally DROP the initial table.

INSERT INTO table_1
    SELECT * FROM table_all
             WHERE sql_id % 3 = 0;   -- 0 for table_1. 1 for table_2, 2 for table_3 


If you are adding to tables1/2/3, and they have an AUTO_INCREMENT, you can get unique ids by _skipping sql_id in the transfer:

INSERT INTO table_1 (b,c,d,e)
    SELECT b,c,d,e FROM table_all
             WHERE sql_id % 3 = 0;


This assumes the columns in table_all are 

sql_id,b,c,d,e


And table_1/2/3 have another column that is AUTO_INCREMENT.