For InnoDB, the following seems to work: create the new empty database, then rename each table in turn into the new database:
RENAME TABLE old_db.table TO new_db.table;
You will need to adjust the permissions after that.
For scripting in a shell, you can use either of the following:
mysql -u username -ppassword old_db -sNe 'show tables' | while read table; \
do mysql -u username -ppassword -sNe "rename table old_db.$table to new_db.$table"; done
OR
for table in `mysql -u root -ppassword -s -N -e "use old_db;show tables from old_db;"`; do mysql -u root -ppassword -s -N -e "use old_db;rename table old_db.$table to new_db.$table;"; done;
Notes:
- There is no space between the option
-p and the password. If your database has no password, remove the -u username -ppassword part.
If some table has a trigger, it cannot be moved to another database using above method (will result Trigger in wrong schema error). If that is the case, use a traditional way to clone a database and then drop the old one:
mysqldump old_db | mysql new_db
If you have stored procedures, you can copy them afterwards:
mysqldump -R old_db | mysql new_db
You can use GROUP_CONCAT:
SELECT person_id,
GROUP_CONCAT(hobbies SEPARATOR ', ')
FROM peoples_hobbies
GROUP BY person_id;
As Ludwig stated in his comment, you can add the DISTINCT operator to avoid duplicates:
SELECT person_id,
GROUP_CONCAT(DISTINCT hobbies SEPARATOR ', ')
FROM peoples_hobbies
GROUP BY person_id;
As Jan stated in their comment, you can also sort the values before imploding it using ORDER BY:
SELECT person_id,
GROUP_CONCAT(hobbies ORDER BY hobbies ASC SEPARATOR ', ')
FROM peoples_hobbies
GROUP BY person_id;
As Dag stated in his comment, there is a 1024 byte limit on the result. To solve this, run this query before your query:
SET group_concat_max_len = 2048;
Of course, you can change 2048 according to your needs. To calculate and assign the value:
SET group_concat_max_len = CAST(
(SELECT SUM(LENGTH(hobbies)) + COUNT(*) * LENGTH(', ')
FROM peoples_hobbies
GROUP BY person_id) AS UNSIGNED);
Best Solution
You can't compare them like that. Or at least, you shouldn't. Each one uses the memory in a different way. This is especially true if you're tunning your DB's for performance.
MyISAM has specific buffers for indexes and it uses the OS disk buffer for caching other data. It doesn't make sense to have your buffers larger than the sum of your indexes, but the more memory you give it, the faster it will be.
InnoDB has a buffer pool for all data. You configure this based on your available memory and how much you want to give it. InnoDB buffers as much of your data in memory as possible. If you can fit the entire DB in memory, InnoDB will never read from disk. A lot of InnoDB databases see huge performance hits when the data size becomes larger than the buffer pool.
MySQL is very configurable. It's tunable to meet your needs. Typically, databases should be given as much memory as possible since they are almost always disk bound. More memory means more can be buffered.