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

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}
    };
    return p_non_generate_options.parse(pos, node, expected);
}
bool ParserDeclareColumn::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
{
    ASTPtr column_name;
    ASTPtr column_data_type;
    ASTPtr column_options;
    ParserExpression p_expression;
    ParserIdentifier p_identifier;
    if (!p_identifier.parse(pos, column_name, expected))
        return false;
    if (!ParserDataType().parse(pos, column_data_type, expected))
        return false;
    parseColumnDeclareOptions(pos, column_options, expected);
    auto declare_column = std::make_shared<ASTDeclareColumn>();
    declare_column->name = getIdentifierName(column_name);
    declare_column->data_type = column_data_type;
    declare_column->column_options = column_options;
    if (declare_column->data_type)
        declare_column->children.emplace_back(declare_column->data_type);
    if (declare_column->column_options)
        declare_column->children.emplace_back(declare_column->column_options);
    node = declare_column;
    return true;
}
}
}