Clickhouse: [Exception] when use union all with constant throw DB::Exception: Cannot convert column

[lamber-ken]

version 1.1.54383, version 1.1.54342
union all with constant from distributed table, throw exception

a minimal reproducible example
``` create table
CREATE TABLE datacenter.testunionalla_shard ON CLUSTER datacenter
(
a String
)
ENGINE = Log;

CREATE TABLE datacenter.testunionalla ON CLUSTER datacenter
(
a String
)
ENGINE = Distributed(datacenter, datacenter, testunionalla_shard, rand());

``` select
SELECT count()
FROM 
(
    SELECT 
        'aa' AS tt, 
        a
    FROM datacenter.testunionalla 
    UNION ALL
    SELECT 
        'aa' AS tt, 
        a
    FROM datacenter.testunionalla 
) ;

Received exception from server (version 1.1.54383):
Code: 171. DB::Exception: Received from clickhouse-server-test DB::Exception: Cannot convert column tt because it is non constant in source stream but must be constant in result. 

[dengwanc]

select uid, if(toUInt8(uid), 's', 'v') as t from nxlog.table limit 10
union all
select uid, if(toUInt8(uid), 's', 'v') as s from nxlog.table limit 10

worked but stupid

[alexey-milovidov]

It the datacenter cluster contains local shard?

[lamber-ken]

@alexey-milovidov , yes.
the name of cluster is datacenter.
the name of database is datacenter too.

cluster's config

SELECT *
FROM system.clusters 

┌─cluster────┬─shard_num─┬─shard_weight─┬─replica_num─┬─host_name──────┬─port─┬─is_local─┬─user────┬─default_database─┐
│ datacenter │         1 │            1 │           1 │ hadoop-180-111 │ 9000 │        1 │ default │                  │
│ datacenter │         2 │            1 │           1 │ hadoop-180-112 │ 9000 │        0 │ default │                  │
│ datacenter │         3 │            1 │           1 │ hadoop-180-113 │ 9000 │        0 │ default │                  │
│ datacenter │         4 │            1 │           1 │ hadoop-180-114 │ 9000 │        0 │ default │                  │
│ datacenter │         5 │            1 │           1 │ hadoop-180-115 │ 9000 │        0 │ default │                  │
└────────────┴───────────┴──────────────┴─────────────┴────────────────┴───────────────┴──────┴──────────┴─────────┴──────────────────┘

[filimonov]

Problem is still here.

Simple test case:

SELECT 
    'settings' AS source, 
    *
FROM system.settings
UNION ALL
SELECT 
    'settings' AS source, 
    *
FROM remote('127.0.0.1', 'system', 'settings')

Received exception from server (version 19.13.3):
Code: 171. DB::Exception: Received from localhost:9000. DB::Exception: Cannot convert column source because it is non constant in source stream but must be constant in result. Stack trace:

0. /usr/bin/clickhouse-server(StackTrace::StackTrace()+0x30) [0x7f6b5f0]
1. /usr/bin/clickhouse-server(DB::Exception::Exception(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, int)+0x25) [0x3c46865]
2. /usr/bin/clickhouse-server() [0x3a3ba35]
3. /usr/bin/clickhouse-server(DB::InterpreterSelectWithUnionQuery::executeWithMultipleStreams()+0x1aa) [0x6d8abda]
4. /usr/bin/clickhouse-server(DB::InterpreterSelectWithUnionQuery::execute()+0x38) [0x6d8c958]
5. /usr/bin/clickhouse-server() [0x6e98ff1]
6. /usr/bin/clickhouse-server(DB::executeQuery(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, DB::Context&, bool, DB::QueryProcessingStage::Enum, bool)+0xfc) [0x6e9a14c]
7. /usr/bin/clickhouse-server(DB::TCPHandler::runImpl()+0x9fa) [0x3c87fba]
8. /usr/bin/clickhouse-server(DB::TCPHandler::run()+0x2b) [0x3c8887b]
9. /usr/bin/clickhouse-server(Poco::Net::TCPServerConnection::start()+0x10) [0x793f490]
10. /usr/bin/clickhouse-server(Poco::Net::TCPServerDispatcher::run()+0xed) [0x793fbad]
11. /usr/bin/clickhouse-server(Poco::PooledThread::run()+0x81) [0x806a4e1]
12. /usr/bin/clickhouse-server(Poco::ThreadImpl::runnableEntry(void*)+0x3c) [0x806828c]
13. /usr/bin/clickhouse-server() [0xba3e1a0]
14. /lib/x86_64-linux-gnu/libpthread.so.0(+0x76db) [0x7f409eebb6db]
15. /lib/x86_64-linux-gnu/libc.so.6(clone+0x3f) [0x7f409e64288f]


0 rows in set. Elapsed: 0.006 sec. 

Workaround - is to use materialize function:

select 'settings' as source, * from system.settings union all select materialize('settings') as source, * from remote('127.0.0.1','system','settings') ; 

[alexey-milovidov]

Fixed in master.