How to generate Symfony fixtures YML from exising database data

Try:

INSERT INTO table1 ( column1 )
SELECT  col1
FROM    table2  

This is standard ANSI SQL and should work on any DBMS

It definitely works for:

• Oracle
• MS SQL Server
• MySQL
• Postgres
• SQLite v3
• Teradata
• DB2
• Sybase
• Vertica
• HSQLDB
• H2
• AWS RedShift
• SAP HANA
• Google Spanner

Inserts, updates, deletes and reads are generally OK from multiple threads, but Brad's answer is not correct. You have to be careful with how you create your connections and use them. There are situations where your update calls will fail, even if your database doesn't get corrupted.

The basic answer.

The SqliteOpenHelper object holds on to one database connection. It appears to offer you a read and write connection, but it really doesn't. Call the read-only, and you'll get the write database connection regardless.

So, one helper instance, one db connection. Even if you use it from multiple threads, one connection at a time. The SqliteDatabase object uses java locks to keep access serialized. So, if 100 threads have one db instance, calls to the actual on-disk database are serialized.

So, one helper, one db connection, which is serialized in java code. One thread, 1000 threads, if you use one helper instance shared between them, all of your db access code is serial. And life is good (ish).

If you try to write to the database from actual distinct connections at the same time, one will fail. It will not wait till the first is done and then write. It will simply not write your change. Worse, if you don’t call the right version of insert/update on the SQLiteDatabase, you won’t get an exception. You’ll just get a message in your LogCat, and that will be it.

So, multiple threads? Use one helper. Period. If you KNOW only one thread will be writing, you MAY be able to use multiple connections, and your reads will be faster, but buyer beware. I haven't tested that much.

Here's a blog post with far more detail and an example app.

• Android Sqlite Locking (Updated link 6/18/2012)
• Android-Database-Locking-Collisions-Example by touchlab on GitHub

Gray and I are actually wrapping up an ORM tool, based off of his Ormlite, that works natively with Android database implementations, and follows the safe creation/calling structure I describe in the blog post. That should be out very soon. Take a look.

In the meantime, there is a follow up blog post:

• Single SQLite connection

Also checkout the fork by 2point0 of the previously mentioned locking example:

• Android-Database-Locking-Collisions-Example by 2point0 on GitHub