SELECT DATE$\_$ADD$(\text{'}2020-01-01\text{'},$ INTERVAL $($ones$.$num $+$ tens.num $+$ hundreds.num$)$ DAY$)$ dt

FROM

$($SELECT $0$ num UNION ALL

SELECT $1$ num UNION ALL

SELECT $2$ num UNION ALL

SELECT $3$ num UNION ALL

SELECT $4$ num UNION ALL

SELECT $5$ num UNION ALL

SELECT $6$ num UNION ALL

SELECT $7$ num UNION ALL

SELECT $8$ num UNION ALL

SELECT $9$ num$)$ ones

CROSS JOIN

$($SELECT $0$ num UNION ALL

SELECT $10$ num UNION ALL

SELECT $20$ num UNION ALL

SELECT $30$ num UNION ALL

SELECT $40$ num UNION ALL

SELECT $50$ num UNION ALL

SELECT $60$ num UNION ALL

SELECT $70$ num UNION ALL

SELECT $80$ num UNION ALL

SELECT $90$ num$)$ tens

CROSS JOIN

$($SELECT $0$ num UNION ALL

SELECT $100$ num UNION ALL

SELECT $200$ num UNION ALL

SELECT $300$ num$)$ hundreds

WHERE DATE$\_$ADD$(\text{'}2020-01-01\text{'},$

INTERVAL $($ones$.$num $+$ tens.num $+$ hundreds.num$)$ DAY$)<\text{'}2021-01-01\text{'}$

ORDER BY $1$;

$$

$(1)$ Please explain the result of the above query

$(2)$ Please explain the purpose of the where clause:

WHERE DATE$\_$ADD$(\text{'}2020-01-01\text{'},$INTERVAL $($ones$.$num $+$ tens.num $+$ hundreds.num$)$ DAY$)<\text{'}2021-01-01\text{'}$