MySQL 8.0

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CREATE TABLE mytable(
   date  DATE  NOT NULL PRIMARY KEY
  ,score INTEGER  NOT NULL
);
INSERT INTO mytable(date,score) VALUES ('2010-08-01',19);
INSERT INTO mytable(date,score) VALUES ('2010-08-02',21);
INSERT INTO mytable(date,score) VALUES ('2010-08-04',14);
INSERT INTO mytable(date,score) VALUES ('2010-08-07',10);
INSERT INTO mytable(date,score) VALUES ('2010-08-10',14);
with recursive all_dates(dt) as (
    -- anchor
    select '2010-08-01' dt
    union all 
    -- recursion with stop condition
    select dt + interval 1 day from all_dates where dt < '2010-08-15'
)
select * from all_dates order by dt


dt


2010-08-01

2010-08-02

2010-08-03

2010-08-04

2010-08-05

2010-08-06

2010-08-07

2010-08-08

2010-08-09

2010-08-10

2010-08-11

2010-08-12

2010-08-13

2010-08-14

2010-08-15


with recursive all_dates(dt) as (
    select '2010-08-01' dt
    union all 
    select dt + interval 1 day from all_dates where dt < '2010-08-15'
)
select d.dt date, coalesce(t.score, 0) score
from all_dates d
left join mytable t on t.date = d.dt
order by d.dt


date
score


2010-08-01
19

2010-08-02
21

2010-08-03
0

2010-08-04
14

2010-08-05
0

2010-08-06
0

2010-08-07
10

2010-08-08
0

2010-08-09
0

2010-08-10
14

2010-08-11
0

2010-08-12
0

2010-08-13
0

2010-08-14
0

2010-08-15
0

date	score
2010-08-01	19
2010-08-02	21
2010-08-03	0
2010-08-04	14
2010-08-05	0
2010-08-06	0
2010-08-07	10
2010-08-08	0
2010-08-09	0
2010-08-10	14
2010-08-11	0
2010-08-12	0
2010-08-13	0
2010-08-14	0
2010-08-15	0