Merging two MySql tables

How to merge two MySql tables that have the same structure and were the primary keys of the two tables will clash.

One option is:

    INSERT IGNORE
    INTO table_1
    SELECT *
    FROM table_2;

which allows those rows in table_1 to supersede those in table_2 that have a matching primary key, while still inserting rows with new primary keys.

Alternatively,

  
     REPLACE
     INTO table_1
     SELECT *
     FROM table_2;

will update those rows already in table_1 with the corresponding row from table_2, while inserting rows with new primary keys.