Since client process the INSERT block itself, and only after, send it
to the client, for example:
clickhouse-client --stacktrace --input_format_null_as_default=1 --query="INSERT INTO FUNCTION null('k Int, v Tuple(Int,Int)') VALUES ()"
Code: 62. DB::Exception: Cannot parse expression of type Int32 here: ): While executing ValuesBlockInputFormat: (in query: INSERT INTO FUNCTION null('k Int, v Tuple(Int,Int)') VALUES ()): data for INSERT was parsed from query. (SYNTAX_ERROR), Stack trace (when copying this message, always include the lines below):
Before this patch the query `(k,v) IN ((1, 2))` was transformed `(k,v)
IN (1,2)` by ClickHouse, and this produce the following error while
sending such query to MySQL:
DB::Exception: mysqlxx::BadQuery: Operand should contain 2 column(s)
(There is a workaround though, add another value for IN section, i.e.
`(k,v) IN ((1,2),(0,0))`, but this is icky)
v0: (k,v) IN ((1,2)) -> (k,v) IN tuple((1,2))
But these is not supported by transformQueryForExternalDatabase()
v1: (k,v) IN ((1,2)) -> (k,v) IN ((1,2))
But now you will get an error for the following query:
SELECT ('foo', 'bar') IN (('foo', 'bar'))
Now you will get:
Logical error: 'Trying to get name of not a column: ExpressionList'.
(from two places, first is DB::ActionsMatcher::visit, easy to fix by
inherit ASTExpressionList from ASTWithAlias, but the second is
evaluteConstantExpression(), which requires additional support for
these case while creating a set in DB::createBlockForSet())
v2: (k,v) IN ((1,2)) -> (k,v) IN tuple((1,2))
So instead I prefer these, and add support for this case in
transformQueryForExternalDatabase() in the next patch.
It is possible to trigger
MaterializedMySQLSyncThread::stopSynchronization() from the same thread
in case of some exception at startup, when some interpreter holds the
storage refcnt, and later MaterializedMySQLSyncThread will try to join
itself from the main thread.
Here is a stack trace for example:
<details>
4 0x000000000f7ae45c in Poco::Event::wait (this=0x7f1b90c38170) at ../contrib/poco/Foundation/include/Poco/Event.h:97
5 ThreadFromGlobalPool::join (this=0x7f1b90c23120) at ../src/Common/ThreadPool.h:210
6 DB::MaterializeMySQLSyncThread::stopSynchronization (this=0x7f1b8024ca68) at ../src/Databases/MySQL/MaterializeMySQLSyncThread.cpp:229
7 DB::MaterializeMySQLSyncThread::~MaterializeMySQLSyncThread (this=0x7f1b8024ca68) at ../src/Databases/MySQL/MaterializeMySQLSyncThread.cpp:85
8 0x000000000f816dc8 in DB::DatabaseMaterializeMySQL<DB::DatabaseAtomic>::~DatabaseMaterializeMySQL (this=0x7f1b8024c918) at ../src/Databases/MySQL/DatabaseMaterializeMySQL.h:21
11 std::__1::shared_ptr<DB::IDatabase>::~shared_ptr (this=<optimized out>) at ../contrib/libcxx/include/memory:3212
12 0x000000000f8726a6 in DB::InterpreterCreateQuery::createTable (this=<optimized out>, create=...) at ../src/Interpreters/InterpreterCreateQuery.cpp:952
13 0x000000000f87735c in DB::InterpreterCreateQuery::execute (this=0x7f1aeef59860) at ../src/Interpreters/InterpreterCreateQuery.cpp:1225
14 0x000000000fe22253 in DB::executeQueryImpl (begin=<optimized out>, end=<optimized out>, context=..., internal=true, stage=DB::QueryProcessingStage::Complete, has_query_tail=<optimized out>, istr=<optimized out>) at ../src/Interpreters/executeQuery.cpp:574
15 0x000000000fe208e3 in DB::executeQuery (query=..., context=..., internal=<optimized out>, stage=DB::QueryProcessingStage::FetchColumns, may_have_embedded_data=<optimized out>) at ../src/Interpreters/executeQuery.cpp:933
16 0x000000000faafcde in DB::MySQLInterpreter::InterpreterMySQLDDLQuery<DB::MySQLInterpreter::InterpreterCreateImpl>::execute (this=<optimized out>) at ../src/Interpreters/MySQL/InterpretersMySQLDDLQuery.h:75
17 0x000000000faade78 in DB::InterpreterExternalDDLQuery::execute (this=<optimized out>) at ../src/Interpreters/InterpreterExternalDDLQuery.cpp:64
18 0x000000000fe22253 in DB::executeQueryImpl (begin=<optimized out>, end=<optimized out>, context=..., internal=true, stage=DB::QueryProcessingStage::Complete, has_query_tail=<optimized out>, istr=<optimized out>) at ../src/Interpreters/executeQuery.cpp:574
19 0x000000000fe208e3 in DB::executeQuery (query=..., context=..., internal=<optimized out>, stage=DB::QueryProcessingStage::FetchColumns, may_have_embedded_data=<optimized out>) at ../src/Interpreters/executeQuery.cpp:933
20 0x000000000f7ba406 in DB::tryToExecuteQuery (query_to_execute=..., query_context=..., database=..., comment=...) at ../src/Databases/MySQL/MaterializeMySQLSyncThread.cpp:69
21 0x000000000f7d4b88 in DB::dumpDataForTables() (connection=..., query_prefix=..., database_name=..., mysql_database_name=..., context=..., is_cancelled=..., need_dumping_tables=...) at ../src/Databases/MySQL/MaterializeMySQLSyncThread.cpp:326
22 DB::MaterializeMySQLSyncThread::prepareSynchronized(DB::MaterializeMetadata&)::$_1::operator()() const (this=<optimized out>) at ../src/Databases/MySQL/MaterializeMySQLSyncThread.cpp:391
29 DB::commitMetadata() (function=..., persistent_tmp_path=..., persistent_path=...) at ../src/Databases/MySQL/MaterializeMetadata.cpp:197
30 0x000000000f80a000 in DB::MaterializeMetadata::transaction(DB::MySQLReplication::Position const&, std::__1::function<void ()> const&) (this=0x7f1b6375c3d8, position=..., fun=...) at ../src/Databases/MySQL/MaterializeMetadata.cpp:230
31 0x000000000f7b2231 in DB::MaterializeMySQLSyncThread::prepareSynchronized (this=0x7f1b8024ca68, metadata=...) at ../src/Databases/MySQL/MaterializeMySQLSyncThread.cpp:388
32 0x000000000f7b169c in DB::MaterializeMySQLSyncThread::synchronization (this=0x7f1b8024ca68) at ../src/Databases/MySQL/MaterializeMySQLSyncThread.cpp:180
33 0x000000000f7d4074 in DB::MaterializeMySQLSyncThread::startSynchronization()::$_0::operator()() const (this=<optimized out>) at ../src/Databases/MySQL/MaterializeMySQLSyncThread.cpp:236
</details>
Nested identical combinators (i.e. uniqCombinedIfIf) is not
supported (since they even don't work -- silently).
But non-identical does supported and works, for example
uniqCombinedIfMergeIf, it is useful in case when the underlying
storage stores AggregateFunction(uniqCombinedIf) and in SELECT you
need to filter aggregation result based on another column for
example.
Second If combinator can be useful to add condition based on another
column, when Merge combinator is applied for example (i.e.
uniqCombinedIfMergeIf(state_of_merge_that_is_stored_in_table, event_date = today())).
