I'm beginning in SQL and don't know how to do that.
What I am looking for is a way to give the same ID to column which as an identical value.
This is my table :
I want 'afrique du sud' for exemple to have the same 'id_country'
How can I do that ?
I tried SELECT DISTINCT country FROM country SET id_country = id_country + 1 but it didn't work and I guess it is because SELECT don't mix up the value (that would make sense).
Any help would be gladly accepted.
You need to set up a separate table called country. It will have 2 columns where each country will have an individual id and a name. You can then set the id_country to the id from the country table with the following:
UPDATE table t, country_table c SET t.id_country = c.id WHERE t.country = c.name
The first thing you want to do is to group your table by country, and always select the maximum id for each country.
SELECT description_country, max(id) id
FROM country
GROUP BY description_country
When you have this you want to update your original table with the id that came out of the previous query where the description matches.
UPDATE country c
SET ID_COUNTRY=X.id
FROM
(SELECT description_country, max(id) id
FROM country
GROUP BY description_country) X
WHERE c.description_country = x.description_country
you can use this query:
update country_table set id_country =
(select max_id from (select max(id) as max_id, country from country_table group by country_table.country ) as temp_table
where temp_table.country = country_table.country)
Related
I need to fetch the 3 lines as highlighted in the result with green i.e separate region id but same kivuto id.I need to rectify such products so that I could correct the kivuto id's
Try this.
select * from table_name
where kivuto_id in (
select email from table_name
group by kivuto_id
having count(*) > 1
)
You can refer to this as well: Find rows that have the same value on a column in MySQL
You can simply use exists:
select t.*
from t
where exists (select 1
from t t2
where t2.kivuto_id = t.kivuto_id and
t2.region_id <> t.region_id
);
For performance, you want an index on (kivuto_id, region_id).
select max(c),
name
from(
select
name,
count(*) as c
from(
book join owns using (title)
)
join person using(ssn)
where author='X'
groupby (name)
) as counts:
But it showing max count and first name in the table instead of corresponding name.
Here it shows output manny 14, but it showing max value but first name in the table you can find that in below picture.
I think you can try this -
Instead of giving
select max(c), name
give,
select c, name
...
order by c desc limit 1;
I am not sure how to do this in mysql, i have searched but I can't seem to find a solution.
,
I have a table like so.
id pid occurrence
1 23 blank
2 23 blank
3 44 blank
Basically, occurrence should have the value of 2, for id 1,2 and a value of 1 for id 3.
Any help would be appreciated. I can easily call count and GROUP BY, and get the number of times each one occurance, but I would like to update column occurrence in the right place for each pid.
To get the correct occurrence value you can do
select pid, count(*) as occurrence
from your_table
group by pid
To update the table do
update your_table t1
join
(
select pid, count(*) as occurrence
from your_table
group by pid
) t2 on t1.pid = t2.pid
set t1.occurrence = t2.occurrence
If you want to set the value in the table, use update with a join:
update table t join
(select pid, count(*) as cnt
from table
group by pid
) tt
on tt.pid = t.pid
set t.occurrence = tt.cnt;
I have a MySQL table where I have a certain id as a foreign key coming from another table. This id is not unique to this table so I can have many records holding the same id.
I need to find out which ids are seen the least amount of times in this table and pull up a list containing them.
For example, if I have 5 records with id=1, 3 records with id=2 and 3 records with id=3, I want to pull up only ids 2 & 3. However, the data in the table changes quite often so I don't know what that minimum value is going to be at any given moment. The task is quite trivial if I use two queries but I'm trying to do it with just one. Here's what I have:
SELECT id
FROM table
GROUP BY id
HAVING COUNT(*) = MIN(SELECT COUNT(*) FROM table GROUP BY id)
If I substitute COUNT(*) = 3, then the results come up but using the query above gives me an error that MIN is not used properly. Any tips?
I would try with:
SELECT id
FROM table
GROUP BY id
HAVING COUNT(*) = (SELECT COUNT(*) FROM table GROUP BY id ORDER BY COUNT(*) LIMIT 1);
This gets the minimum selecting the first row from the set of counts in ascendent order.
You need a double select in the having clause:
SELECT id
FROM table
GROUP BY id
HAVING COUNT(*) = (SELECT MIN(cnt) FROM (SELECT COUNT(*) as cnt FROM table GROUP BY id) t);
The MIN() aggregate function is suposed to take a column, not a query. So, I see two ways to solve this:
To properly write the subquery, or
To use temp variables
First alternative:
select id
from yourTable
group by id
having count(id) = (
select min(c) from (
select count(*) as c from yourTable group by id
) as a
)
Second alternative:
set #minCount = (
select min(c) from (
select count(*) as c from yourTable group by id
) as a
);
select id
from yourTable
group by id
having count(*) = #minCount;
You need to GROUP BY to produce a set of grouped values and additional select to get the MIN value from that group, only then you can match it against having
SELECT * FROM table GROUP BY id
HAVING COUNT(*) =
(SELECT MIN(X.CNT) AS M FROM(SELECT COUNT(*) CNT FROM table GROUP BY id) AS X)
I have collected informations from different sources about certain IDs that should match a single name. Some sources are more trustworthy than others in giving the correct name for a given ID.
I created a table (name, id, source_trustworthiness) and I want to get the most trustworthy name for each ID.
I tried
SELECT name, id, MAX( source_trustworthiness )
FROM table
GROUP BY id
this returns th highest trustworthiness available for each ID but with the first name it finds, regarless of its trustworthiness.
Is there a way I can get that right ?
Mysql has special functionality to help:
SELECT * FROM (
SELECT name, id, source_trustworthiness
FROM table
ORDER BY 3 DESC ) x
GROUP BY id
Although this wouldn't even execute in other databases (not naming all non-aggregate columns in the GROUP BY clause), with mysql it returns the first row encountered for each unique value of the grouped by columns. By ordering the rows greatest first, the first row for each id will be the most trustworthy.
Since this question is tagged mysql, this query is OK. Not only is it really simple, it's also quite fast.
SELECT a.*
FROM TableName a
INNER JOIN
(
SELECT id, MAX(source_trustworthiness) max_val
FROM TableName
GROUP BY ID
) b ON a.ID = b.ID AND
a.source_trustworthiness = b.max_val