I would like to merge two very large MyISAM tables (with the same structure) and a unique key on 3 columns. Is it possible to create the table where they are going to be merged WITHOUT the unique key, merge the tables' contents, and only then add the unique key in the resulting table, with the effect of ON DUPLCATE KEY UPDATE another field? So, to summarize, I have:

```
Table 1 - Fields f1,f2,f3,f4 (Unique Key on f1,f2,f3)
Table 2 - Fields f1,f2,f3,f4 (Unique Key on f1,f2,f3)
Table 3 - Where Table 1 and Table 2 will be merged, 
          with fields f1,f2,f3,f4 and NO unique key.

```

So then I want to merge Table 1 and 2 into Table 3 and only after the merge is complete, I want to add a unique key (f1,f2,f3) on Table 3 ON DUPLICATE KEY UPDATE f4=f4+1...(i.e. The result desired is that of INSERTing rows from Table 1 and Table 2 into Table 3 (with a preexisting unique key on f1,f2,f3) and ON DUPLICATE KEY UPDATE f4=f4+1 but creating the key in Table 3 only after all the Table 1 and Table 2 rows have been inserted). Is this possible?