Function getMapKeyField

src/Interpreters/QueryNormalizer.cpp:104–138

* Convert key according to map key type. * For some types, like Enum, Date, DateTime which can be map key type, they need to convert to correct Field. Otherwise, query will be wrong. * For example, there has one map column named a and one row data * a Map(Date, UInt64) KV : {'2022-05-31': 1}) * Here we query for key '2022-05-31', but in fact, the Date type is essentially

     * After conversion, here we query for key 19143 which can be handled correctly.
     */
    Field getMapKeyField(ASTFunction & node, QueryNormalizer::Data & data, const DataTypePtr & key_type)
    {
        ASTLiteral * key_lit = node.arguments->children[1]->as<ASTLiteral>(); // Constant Literal
        ASTFunction * key_func = node.arguments->children[1]->as<ASTFunction>(); // for constant foldable functions' case

        Field res = Null();
        if (key_lit) // key is literal
        {
            Field key_field = tryConvertToMapKeyField(key_type, key_lit->getColumnName());
            /// return origin key field if failed to convert to map key field, so the ast can be rewritten multi-times
            return key_field.isNull() ? key_lit->value : key_field;
        }
        else if (key_func)
        {
            /// check whether key_func's inputs are all constant literal, if yes, invoke constant folding logic.
            /// This handling is specially added for Date key which is toDate('YYYY-MM_DD') in SQL
            bool all_input_const = true;
            for (auto & c : key_func->arguments->children)
            {
                if (!c->as<ASTLiteral>())
                {
                    all_input_const = false;
                    break;
                }
            }

            if (all_input_const)
            {
                std::pair<Field, DataTypePtr> value_raw = evaluateConstantExpression(node.arguments->children[1], data.context);
                res = value_raw.first;
            }
        }

        return res;
    }

    void rewriteMapElement(ASTPtr & ast, const String & map_name, const String & key_name)
    {