Reproduction steps:
```
CREATE TABLE table_left                                                                                                                                                                                              
(                                                                                                                                                                                                                    
    `date` Date,                                                                                                                                                                                                     
    `uid` String                                                                                                                                                                                                     
)                                                                                                                                                                                                                    
ENGINE = MergeTree()                                                                                                                                                                                                 
ORDER BY (date, uid)          
                                                                                                                                                                                       
CREATE TABLE table_right                                                                                                                                                                                             
(                                                                                                                                                                                                                    
    `date` Date,                                                                                                                                                                                                     
    `value` Decimal(18, 10)                                                                                                                                                                                          
)                                                                                                                                                                                                                    
ENGINE = MergeTree()                                                                                                                                                                                                 
ORDER BY date

INSERT INTO table_left values(toDate('2019-10-01'), 'hello');
INSERT INTO table_right values (toDate('2019-10-01'), 1), (toDate('2029-10-01'), 2);

SET join_use_nulls = 1;

SELECT ifNull(subquery_right.alias_value, 0)
FROM table_left
FULL OUTER JOIN 
(
    SELECT
        date,
        value AS alias_value
    FROM table_right
) AS subquery_right
ON table_left.date = subquery_right.date

Received exception from server (version 21.3.1):
Code: 43. DB::Exception: Received from localhost:9000. DB::Exception: Incompatible types of arguments corresponding to two conditional branches: while executing 'FUNCTION ifNull(alias_value :: 0, 0 :: 1) -> ifNull(alias_value, 0) Decimal(18, 10) : 2'. 
```
{
public:
    static constexpr auto name = "if";
    static FunctionPtr create(ContextPtr) { return std::make_shared<FunctionIf>(); }
private:
    template <typename T0, typename T1>
    static UInt32 decimalScale(const ColumnsWithTypeAndName & arguments [[maybe_unused]])
    {
        if constexpr (IsDecimalNumber<T0> && IsDecimalNumber<T1>)
        {
            UInt32 left_scale = getDecimalScale(*arguments[1].type);
            UInt32 right_scale = getDecimalScale(*arguments[2].type);
            if (left_scale != right_scale)
                throw Exception("Conditional functions with different Decimal scales", ErrorCodes::NOT_IMPLEMENTED);
            return left_scale;
        }
        else
            return std::numeric_limits<UInt32>::max();
    }
    template <typename T0, typename T1, typename ColVecT0, typename ColVecT1>
    ColumnPtr executeRightType(