MySQL MERGE存储引擎 - DROP＆ALTER

Question

I need to Add & Delete merged tables in the UNION=() line. According to the MySQL docs it says:

1. DROP the MERGE table and re-create it.
2. Use ALTER TABLE tbl_name UNION=(...) to change the list of underlying tables.

The only "DROP" I'm aware of is DROP TABLE tablename; Are these instructions suggesting that I drop the MRG_MyISAM table, then recreate it with an empty UNION=() field? To then be followed by an ALTER TABLE tbl_name UNION=(...) with all the tables I need to have connected?

If possible, could you post an example of the commands?

Thanks

Answer 1

Oh boy, am I late here. But this page is in the top google search results for "alter table tbl_name union=(...)". So I guess it needs an answer

So here's the answer. To change the union list of underlying tables for merge table you only need to execute this statement

alter table tbl_name union=(`t1`,`t2`,`t3`);

where t1 , t2 , t3 is a list of tables you want to have in a union.

You can drop merge table and recreate it with a new list of underlying tables. Drop statement execute on merge table will only delete the merge table itself and won't affect underlying tables.

But altering it should be sufficient. And you don't need to recreate it with empty union, if you ever do that, just use list of tables that you want to have in it.

For more, please refer to documentation:

https://dev.mysql.com/doc/refman/5.7/en/merge-storage-engine.html