Add support for COPY FROM DATABASE statement

[Mytherin]

This PR adds support for a new COPY syntax that allows an entire database to be copied from one attached database to another attached database.

Syntax

COPY FROM DATABASE db1 TO db2;
-- copy only the catalog elements and not any data
COPY FROM DATABASE db1 TO db2 (SCHEMA);

Full example

ATTACH ':memory:' AS db1;
CREATE TABLE db1.integers AS SELECT 42 AS i;
ATTACH ':memory:' AS db2;

COPY FROM DATABASE db1 TO db2;
SELECT * FROM db2.integers;
┌───────┐
│   i   │
│ int32 │
├───────┤
│    42 │
└───────┘

Description

All catalog entries are copied from the source database to the target database. This includes schemas, tables, views, macros, sequences and types. The copy happens in two parts. First all schema elements are copied over. Then, if (SCHEMA) is not specified, all data is copied over from the source database to the target database. Data is copied over internally by essentially running queries in the form of INSERT INTO db2.tbl SELECT * FROM db1.tbl.

Limitations

• Explicitly created indexes (with CREATE INDEX) are not copied.
• More work is needed on dependency ordering, also related to Fix EXPORT/IMPORT DATABASE schema.sql order #8619 and [DependencyManager] Rework internals of the DependencyManager #9715. As a result this might not work correctly when there are e.g. foreign key constraints in the source database.

[carlopi]

Great feature!
I gave this a spin, here some corner cases that could make it into a test / I am not sure what the semantic should be.

• ./build/release/duckdb other.db -c "CREATE TABLE t(i int); COPY FROM DATABASE other TO other;"
  Error: Catalog Error: Table with name "t" already exists!
  Self copy should likely be an error

• ./build/release/duckdb empty.db -c "COPY FROM DATABASE empty TO empty"
  Error: INTERNAL Error: Attempted to dereference unique_ptr that is NULL!

• ./build/release/duckdb empty.db -c "ATTACH 'other.db'; COPY FROM DATABASE empty TO other;"
  Error: INTERNAL Error: Attempted to dereference unique_ptr that is NULL!

• ./build/release/duckdb other.db -c "ATTACH 'empty.db' (READ_ONLY); COPY FROM DATABASE other TO empty (SCHEMA);"
  This succeeds (even though it should not), but schema is not moved.

• ./build/release/duckdb a.db -c "ATTACH 'b.db' (READ_ONLY); COPY FROM DATABASE a TO b ;"
  This fails, good, but either with:
  Error: Invalid Error: Cannot execute statement of type "COPY_DATABASE" on database "empty" which is attached in read-only mode!
  or
  Error: Catalog Error: Table with name "t" already exists!
  depending on the content of b.db

• Should performing copy twice work? Basically, if all tables are there (and with the same content), it should still be OK?

• Override option (unsure of the meaning, maybe not then)?

• Should the syntax allow some way to get the default database? Like COPY FROM DEFAULT DATABASE TO otheror even COPY FROM DATABASE TO other defaults to currently attached DB.

[Mytherin]

Thanks for having a look - I've addressed the comments. Should work more as expected now

[szarnyasg]

I read through the CLI dot commands today. Almost all of the SQLite commands are now supported, except .clone:

.clone NEWDB         Clone data into NEWDB from the existing database

It seems .clone is doing something very similar to COPY FROM DATABASE.