我可以在mysqldump中使用查询吗？

Question

I have a Mysql database on my remote server with several tables. I need to get some of this tables with some of its rows using PHP to a local WPF program which uses SQLite.

The rows i need to get from each table depends of some different values for each table (i mean i must apply a different WHERE clause to every table), and i need to be able to use standar MySQL operations (like LEFT JOIN, UNION, etc).

So far, i am able to dump just 1 table with 1 WHERE clause:

exec('./mysql2sqlite.sh --databases test -u test -pTest --tables users --where "a="' . $a . '" AND b="' . $b . ' | sqlite3 db/file.sqlite');

I think what i need is to be able to execute several queries and then dump all the results inside the mysqldump, is it possible?

Also, is this the right approach to solve this kind of problem? Or should i dump the format of the desire tables first and then dump the desire rows?

PD: I am using this MySQL2SQLite converter.

Answer 1

I would solve the problem by creating a separate temporary database called something like tmp_backup , creating tables that would map your tables but only include the desired rows, and then performing a dump of that database. Example of a temporary database table:

CREATE tmp_backup.customers LIKE real_db.customers;
SELECT c.* FROM real_db.customers  c 
LEFT JOIN real_db.bad_customers o USING(customer_id) WHERE o.customer_id IS NULL

If the tables are big, you could also use views, but you will need to patch mysqldump as it will dump views as views, not as tables. Look for

if (strcmp(table_type, "VIEW") == 0)
    DBUG_VOID_RETURN;

in client/mysqldump.c in the MySQL source, comment it out and recompile. You will find the new binary for mysqldump in the client/ directory and you can just copy into some directory under another name without a full install. This hack should work, although I have not yet verified it - will post an update when I do.

UPDATE - the above hack for mysqldump does work with views - I tested it on 5.5.35, but it should work the same with newer 5.5 and likely 5.6/5.7 versions. After the patch, you do need to give it -t argument to just get the table data with the definitions. So you will do mysqldump --no-data real_db first to get the definitions, and then mysqldump -t tmp_backup to get the view data. Then you can just load the in order (definitions first, then the data) with mysql utility.