carol1287 - 5 months ago 24

C# Question

I am trying to do the following but I cannot manage to get it right yet :(.

I have these tables:

`table1 -> tb1_id, tb1_name`

Sample Data:

--------------

1 group1

2 group2

3 group3

4 group4

5 group5

table2 -> tb2_id, tb2_sector, tb2_tb3_id

Sample Data:

--------------

1 alpha 1

2 beta 2

3 gamma 2

4 delta 2

5 epsilon 4

table3 -> tb3_id, tb3_mid, tb3_section

Sample Data:

--------------

1 234 alpha,beta,gama,delta

This is the output that I am looking for:

`Name Count %`

------ ----- -----

group1 1 25%

group2 3 75%

group3 0 0%

group4 0 0%

group5 0 0%

Basically I need a split a column value delimited by a comma (tb3_section in table3) and then find the right group for each value (table2 gives me the group id to link with table1) and then do a total count by group and get the percentage (assuming total is 100%).

This is the query I tried so far:

I searched for split value samples and found one that does the split by creating a numbers table first:

`create table numbers (`

`n` INT(11) SIGNED

, PRIMARY KEY(`n`)

)

INSERT INTO numbers(n) SELECT @row := @row + 1 FROM

(SELECT 0 UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) t,

(SELECT 0 UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) t2,

(SELECT 0 UNION ALL SELECT 1) t8,

(SELECT @row:=0) ti;

Afterwards, I did this:

`select tb3_section, count(1) from (`

select

tb3_mid,

substring_index(

substring_index(tb3_section, ',', n),

',',

-1

) as tb3_section from table3

join numbers

on char_length(tb3_section)

- char_length(replace(tb3_section, ',', ''))

>= n - 1

) tb3_section_dashboard

group by 1

This doesn't give me the group count. Just does the split of tb3_section but doesn't give me the correct count and equivalent percentage. Any ideas will be much appreciate it thanks a lot.

First of all, I would like to thanks @eggyal for pointing me to the right direction and @Shadow for despise knowing that I was not taking the best approach, he came up with a quick fix to my problem. I managed to change the approach and removed the comma delimited values from table3. Instead now I add multiple rows for each new value (and added a constraint to avoid duplicates).

Now

`Sample Data:`

--------------

1 234 alpha

2 234 beta

3 234 gama

4 234 delta

5 235 alpha

Here is the query I have taken from @shadow sample:

`SELECT t1.tb1_name, COUNT(t3.tb3_section) AS no_per_group,`

COUNT(t3.tb3_section) / t4.no_of_groups AS percentage

FROM t1 left

JOIN t2 ON t1.tb1_id=t2.tb2_tb3_id

INNER JOIN t3 ON t2.tb2_sector=t3.tb3_section>0

JOIN (SELECT COUNT(*) AS no_of_groups

FROM t3 INNER JOIN t2 ON t2.tb2_sector=t3.tb3_section>0) t4

GROUP BY t1.tb1_name

Instead of using

Now I get something like the following but the percentage looks odd and I miss a group that doesn't have a match:

`Name no_per_group percentage`

----- ------------- ----------

group1 2 0.1053

group3 3 0.1579

group4 3 0.1579

group5 3 0.1579

Although still I need something like:

`Name Count %`

------ ----- -----

group1 1 25%

group2 3 75%

group3 0 0%

group4 0 0%

group5 0 0%

Notice that if there is no match in a group, I still need to show that group.

Because I have thousands of records which are different from each other, I need to add another condition:

Answer

The best solution would be to redesign your table structure and move the data in the delimited values list to a separate table.

The quick solution is to utilise MySQL's find_in_set() function.

To get the total count of entries in the messages table (table3):

```
select count(*) as no_of_groups
from t3 inner join t2 on find_in_set(t2.tb2_sector,t3.tb3_section)>0
```

To get the counts per group, add a join to table1 and group by group name. To calculate the percentage, add the above query as a subquery:

```
select t1.tb1_name, count(t3.tb3_section) as no_per_group, count(t3.tb3_section) / t4.no_of_groups as percentage
from t1 left join t2 on t1.tb1_id=t2.tb2_tb3_id
inner join t3 on find_in_set(t2.tb2_sector,t3.tb3_section)>0
join (select count(*) as no_of_groups
from t3 inner join t2 on find_in_set(t2.tb2_sector,t3.tb3_section)>0) t4 --no join condition makes a Cartesian join
group by t1.tb1_name
```