Does SQLite support transactions across multiple databases?

Yes transactions works with different sqlite database and even between sqlite and sqlserver. I have tried it couple of times.

Some links and info

From here - Transaction between different data sources.

Since SQLite ADO.NET 2.0 Provider supports transaction enlistement, not only it is possible to perform a transaction spanning several SQLite datasources, but also spanning other database engines such as SQL Server.

Example:

using (DbConnection cn1 = new SQLiteConnection(" ... ") )using (DbConnection cn2 = new SQLiteConnection(" ... "))using (DbConnection cn3 = new System.Data.SqlClient.SqlConnection( " ... ") )using (TransactionScope ts = new TransactionScope() ){    cn1.Open(); cn2.Open(); cn3.Open();    DoWork1( cn1 );    DoWork2( cn2 );    DoWork3( cn3 );    ts.Complete();}

How to attach a new database:

SQLiteConnection cnn = new SQLiteConnection("Data Source=C:\\myfirstdatabase.db");cnn.Open();using (DbCommand cmd = cnn.CreateCommand()){  cmd.CommandText = "ATTACH DATABASE 'c:\\myseconddatabase.db' AS [second]";  cmd.ExecuteNonQuery();cmd.CommandText = "SELECT COUNT(*) FROM main.myfirsttable INNER JOIN second.mysecondtable ON main.myfirsttable.id = second.mysecondtable.myfirstid";  object o = cmd.ExecuteScalar();}

Yes, SQLite explicitly supports multi-database transactions (see https://www.sqlite.org/atomiccommit.html#_multi_file_commit for technical details). However, there is a fairly large caveat. If the database file is in WAL mode, then:

Transactions that involve changes against multiple ATTACHed databases are atomic for each individual database, but are not atomic across all databases as a set.