Percentage & GROUP BY - sqlite

Question

I'm currently working with a collisions dataset which provides all cases that occur in a given day. My first instinct was to get the totals for a given day, where the output looked something like:
collision_date
SUM(severe_injury_count)
SUM(injured_victims)
2001-02-20
19
785
2001-02-20
12
697
2001-02-20
28
823
2001-02-20
29
871
The above example is the output of the below query:
SELECT collision_date, SUM(severe_injury_count),SUM(injured_victims)
FROM collisions c
GROUP BY collision_date
LIMIT 50,100;
I wanted to calculate a percentage of severe_injury_count/injured_victims, I thought it would be straightforward, therefore I attempted running this query (with a few variations of how I might have calc. the % - once I noticed it wasn't giving me what I intended):
SELECT
collision_date,
SUM(severe_injury_count/injured_victims) AS chance_being_sever_injured,
SUM(severe_injury_count),
SUM(injured_victims),
(severe_injury_count/injured_victims)*100,
(SUM(severe_injury_count)/SUM(injured_victims))*100
FROM collisions c
GROUP BY collision_date;
But the output I've been given does do the calculation as I might have expected, giving me results like:
collision_date
chance_being_sever_injured
SUM(severe_injury_count)
SUM(injured_victims)
(severe_injury_count/injured_victims)*100
(SUM(severe_injury_count)/SUM(injured_victims))*100
2001-02-20
13
19
785
NULL
0
2001-02-20
5
12
697
NULL
0
2001-02-20
17
28
823
0
0
2001-02-20
18
29
871
NULL
0
I checked the variable types and they are all integers and not strings, so I would have expected to have the actual percentages calculated.
Given the output results, I believe that I'm missing something fundamental when doing this type of operation.
I also tried using FORMAT(), but the output were all zero's as well...
FORMAT((SUM(severe_injury_count)/SUM(injured_victims))*100,2)
Any insight would be much appreciated.
Thank you for your time and feedback.
Implementing suggestions, hence extending initial post:
I tried the following as well:
SELECT collision_date, SUM(severe_injury_count),SUM(injured_victims),CAST(SUM(severe_injury_count)/SUM(injured_victims) AS DECIMAL)
FROM collisions c
GROUP BY collision_date
LIMIT 50,100;
Tried also to exclude possible NULL's by:
SELECT collision_date, SUM(severe_injury_count),SUM(injured_victims),CAST(SUM(severe_injury_count)/SUM(injured_victims) AS DECIMAL)
FROM collisions c WHERE severe_injury_count IS NOT NULL OR injured_victims IS NOT NULL
GROUP BY collision_date
LIMIT 50,100;
SELECT collision_date, SUM(severe_injury_count),SUM(injured_victims),CAST(SUM(severe_injury_count)/SUM(injured_victims) AS DECIMAL)
FROM collisions c WHERE severe_injury_count > 0 OR injured_victims > 0
GROUP BY collision_date
LIMIT 50,100;
All the above alternatives give me 0 as values for the "percentage" column I'm trying to calculate.
Also attempted to coerce the type for a given column as suggested by #easleyfixed like so:
SELECT collision_date, SUM(severe_injury_count),SUM(injured_victims),CAST(SUM(CAST(severe_injury_count AS INT))/SUM(CAST(injured_victims AS INT)) AS DECIMAL)
FROM collisions c WHERE severe_injury_count > 0 OR injured_victims > 0
GROUP BY collision_date;
Expanding on #nnichols & #easleyfixed suggestions
To better illustrate the data, running:
SELECT collision_date,COUNT(*)
FROM collisions c
GROUP BY collision_date;
Gives me (represents the number of records for a given date):
collision_date
COUNT(*)
2001-01-01
1000
2001-01-02
1330
2001-01-03
1329
2001-01-04
1346
2001-01-05
1457
etc
etc
I therefore expanded the query to try and include what I'm trying to assess.
SELECT collision_date,COUNT(*),SUM(severe_injury_count),SUM(injured_victims),
SUM(severe_injury_count)/SUM(injured_victims) AS chance_being_sever_injured
FROM collisions c
GROUP BY collision_date;
Outputs:
collision_date
COUNT(*)
SUM(severe_injury_count)
SUM(injured_victims)
SUM(severe_injury_count)/SUM(injured_victims) AS chance_being_sever_injured
2001-01-01
1000
37
676
0
2001-01-02
1330
30
797
0
2001-01-03
1329
28
793
0
2001-01-04
1346
23
758
0
2001-01-05
1457
30
836
0
etc
etc
etc
etc
etc
I double checked the database types and the ones with columns are INT but the collision_date is actually set as "TEXT".
For Sh*t and giggles I did:
SELECT CAST(collision_date AS DATE),COUNT(*),SUM(severe_injury_count),SUM(injured_victims),
SUM(severe_injury_count)/SUM(injured_victims) AS chance_being_sever_injured
FROM collisions c
GROUP BY collision_date;
CAST(collision_date AS DATE)
COUNT(*)
SUM(severe_injury_count)
SUM(injured_victims)
SUM(severe_injury_count)/SUM(injured_victims) AS chance_being_sever_injured
2,001
1000
37
676
0
2,001
1330
30
797
0
2,001
1329
28
793
0
2,001
1346
23
758
0
2,001
1457
30
836
0
etc
etc
etc
etc
etc
Also attempting to coerce NULL's into 0 as also suggested.
SELECT collision_date ,COUNT(*),SUM(IFNULL(severe_injury_count,0)),SUM(IFNULL(injured_victims,0)),
SUM(IFNULL(severe_injury_count,0))/SUM(IFNULL(injured_victims,0)) AS chance_being_sever_injured
FROM collisions c
GROUP BY collision_date;
Outputs:
collision_date
COUNT(*)
SUM(severe_injury_count)
SUM(injured_victims)
SUM(severe_injury_count)/SUM(injured_victims) AS chance_being_sever_injured
2001-01-01
1000
37
676
0
2001-01-02
1330
30
797
0
2001-01-03
1329
28
793
0
2001-01-04
1346
23
758
0
2001-01-05
1457
30
836
0
etc
etc
etc
etc
etc
I'm truly baffled...

Answer 1

MySQL and SQLite are definitely not the same thing! I have updated the tag on your question.
Integer divide yields an integer result, truncated toward zero. docs
You need to cast to REAL or FLOAT for the division to work on SQLite:
SELECT
collision_date,
SUM(severe_injury_count),
SUM(injured_victims),
ROUND(CAST(SUM(severe_injury_count) AS REAL) / CAST(SUM(injured_victims) AS REAL) * 100, 2)
FROM collisions
GROUP BY collision_date
The NULLS observed in one of your tests were the result of division by 0 (zero).