i use
my steps
1. create a new database ckdb on mysql, then  create table t1(a int, primary key(a)); and insert some rows
2. SET allow_experimental_database_materialize_mysql=1; at clickhouse, 
3. CREATE DATABASE ckdb ENGINE = MaterializeMySQL('127.0.0.1:3306', 'ckdb', 'root', 'A123b_456');
4. use ckdb and select * from t1 ok
5. create table dzm as select * from others in mysql ----> cannot see dzm in clickhouse, but if select * from t1, reports
```
Code: 48. DB::Exception: Received from localhost:9000. DB::Exception: The ckdb.dzm cannot be materialized, because there is no primary keys..
```
6. create table t2(a int,b int primary a);----> cannot see t2 in clickhouse, , but if select * from t1, reports
```
Code: 44. DB::Exception: Received from localhost:9000. DB::Exception: Sorting key cannot contain nullable columns.
```
<del>7. if i drop ckdb and recreate it, all tables can be selected </del>
7.if there are some 'bad' tables in a database, all tables in that database cannot be selected

Make sure to check documentation https://clickhouse.yandex/docs/en/ first. If the question is concise and probably has a short answer, asking it in Telegram chat https://telegram.me/clickhouse_en is probably the fastest way to find the answer. For more complicated questions, consider asking them on StackOverflow with "clickhouse" tag https://stackoverflow.com/questions/tagged/clickhouse 

If you still prefer GitHub issues, remove all this text and ask your question here.

{
    const auto & numbers_partition = [&](const String & column_name, bool is_nullable, size_t type_max_size)
    {
        ASTPtr column = std::make_shared<ASTIdentifier>(column_name);
        if (is_nullable)
            column = makeASTFunction("assumeNotNull", column);
        return makeASTFunction("intDiv", column, std::make_shared<ASTLiteral>(UInt64(type_max_size / 1000)));
    };
    ASTPtr best_partition;
    size_t best_size = 0;
    for (const auto & primary_key : primary_keys)
    {
        DataTypePtr type = primary_key.type;
        WhichDataType which(type);
        if (which.isNullable())
        {
            type = (static_cast<const DataTypeNullable &>(*type)).getNestedType();
            which = WhichDataType(type);
        }
        if (which.isDateOrDateTime())
        {
            
            ASTPtr res = std::make_shared<ASTIdentifier>(primary_key.name);
            return makeASTFunction("toYYYYMM", primary_key.type->isNullable() ? makeASTFunction("assumeNotNull", res) : res);