How do I create a COUNT column to count the repetitive values?
And I want to keep the table EXACTLY as below but add the last column (count_id).
The values at the left come from a JOIN so they are "equal".
Thanks! (I tried a lot)
You just want count(*) as a window function:
select t.*,
count(*) over (partition by id, name, department) as count_id
from t;
Related
I want to do a count grouping by the first column but omitting the others columns in the group by. Let me explain:
I have a table with those columns
So, what I want to get is a new column with the work orders total by Instrument, something like this:
How can I do that? Because if I do a count like this:
SELECT INSTRUMENT, WORKORDER, DATE, COUNT(*)
FROM TABLE1
GROUP BY INSTRUMENT, WORKORDER, DATE;
I get this:
Just use a window function:
select t.*,
count(*) over (partition by instrument) as instrument_count
from table1 t;
Although answer given by Gordon is perfect but there is also another option by using group by and subquery. You can add date column to this query as well
SELECT * FROM
(
SELECT A.INSTRUMENT, B.TOTAL_COUNT_BY_INSTRUMENT
FROM work_order A,
(SELECT COUNT(1) AS TOTAL_COUNT_BY_INSTRUMENT,
INSTRUMENT
FROM WORK_ORDER
GROUP BY INSTRUMENT
) B
WHERE A.INSTRUMENT = B.instrument);
fairly new to PostgreSQL and trying out a few count queries. I'm looking to count and count distinct all values in a table. Pretty straightforward -
CountD Count
351 400
With a query like this:
SELECT COUNT(*)
COUNT(id) AS count_id,
COUNT DISTINCT(id) AS count_d_id
FROM table
I see that I can create a single column this way:
SELECT COUNT(*) FROM (SELECT DISTINCT id FROM table) AS count_d_id
But the title (count_d_id) doesn't come through properly and unsure how can I add an additional column. Guidance appreciated
This is the correct syntax:
SELECT COUNT(id) AS count_id,
COUNT(DISTINCT id) AS count_d_id
FROM table
Your original query aliases the subquery rather than the column. You seem to want:
SELECT COUNT(*) AS count_d_id FROM (SELECT DISTINCT id FROM table) t
-- column alias --^ -- subquery alias --^
I have read in various websites about the count() function but I still cannot make this work.
I made a small table with (id, name, last name, age) and I need to retrieve all columns plus a new one. In this new column I want to display how many times a name shows up or repeats itself in the table.
I have made test and can retrieve but only COLUMN NAME with the count column, but I haven't been able to retrieve all data from the table.
Currently I have this
select a.n_showsup, p.*
from [test1].[dbo].[person] p,
(select count(*) n_showsup
from [test1].[dbo].[person])a
This gives me all data on output but on the column n_showsup it gives me just the number of rows, now I know this is because I'm missing a GROUP BY but then when I write group by NAME it shows me a lot of records. This is an example of what I need:
You can use window functions, if you RDBMS supports them:
select t.*, count(*) over(partition by name) n_showsup
from mytable t
Alternatively, you can join the table with an aggregation query that counts the number of occurences of each name:
select t.*, x.n_showsup
from mytable t
inner join (select name, count(*) n_showsup from mytable group by name) x
on x.name = t.name
While the window function approach (#GMB's answer) is the right way to go, thinking through this from a subquery approach (like you were headed towards) would look something like:
select p.*, a.n_showsup
from [test1].[dbo].[person] p
INNER JOIN (
select name, count(*) n_showsup
from [test1].[dbo].[person]
GROUP BY name
) a ON p.name = a.name
This is VERY close to what you had, the difference is that we are grouping that subquery by name (so we get a count by name) and we can use that in the join criteria which we do with the ON clause on that INNER JOIN.
You should really never ever use a comma in your FROM clause. Instead use a JOIN.
I have a table below and want to count the number of consecutive occurrences each letter appears. The code to reproduce the table I am using is listed for those helping to save time.
CREATE TABLE table1 (id integer, names varchar(50));
INSERT INTO table1 VALUES (1,'A');
INSERT INTO table1 VALUES (2,'A');
INSERT INTO table1 VALUES (3,'B');
INSERT INTO table1 VALUES (4,'B');
INSERT INTO table1 VALUES (5,'B');
INSERT INTO table1 VALUES (6,'B');
INSERT INTO table1 VALUES (7,'C');
INSERT INTO table1 VALUES (8,'B');
INSERT INTO table1 VALUES (9,'B');
select * from table1;
I found code already written to accomplish this online, which I've tested and can confirm it runs successfully. It's shown here.
select names, count(*) as count
from (select id, names, (row_number() over (order by id) - row_number() over (partition by names order by id)) as grp
from table1
) as temp
group by grp, names
I am trying to add in the ORDER BY clause at the end, like so:
select names, count(*) as count
from (select id, names, (row_number() over (order by id) - row_number() over (partition by names order by id)) as grp
from table1
) as temp
group by grp, names
order by id -- added this here, but it creates an error.
but kept getting the error "Column "temp.id" is invalid in the ORDER BY clause because it is not contained in either an aggregate function or the GROUP BY clause." However, I am able to order by "names." What is the difference here?
Also, why can't I add in the "order by id" in the subquery? If I run this subquery on its own (see below), then the "order by id" is fine, but all together it cannot run. Why is this?
select names, count(*) as count
from (select id, names, (row_number() over (order by id) - row_number() over (partition by names order by id)) as grp
from table1
order by id -- added this in here, but it creates an error.
) as temp
group by grp, names
order by names
A select statement returns rows in an arbitrary order -- unless it has an order by. This is an extension of the fact that SQL operators on unordered sets.
Your select has no order by, so you should not assume the data would come back in any particular ordering. To get the results order by id, add order by id to the select.
kept getting the error "Column "temp.id" is invalid in the ORDER BY
clause because it is not contained in either an aggregate function or
the GROUP BY clause." However, I am able to order by "names." What is
the difference here?
SQL does things in a certain order. If your query has a GROUP BY (which yours does), that is done first. After grouping, the only thing SQL has is the columns that are selected and grouped by, so those are the only columns that can be used in the order by clause.
As an example, think of houses in a street. If you did a query on houses, returning colour & count, you might get something like Red 2, White 10, Green 3. But asking to sort that by address number makes no sense, because that information is not in data we've returned. In your case you are returning names, count, and you used grp in the group by clause, so those are the only things you can use to sort the final data, because they are all you have, and all that makes sense.
Also, why can't I add in the "order by id" in the subquery? If I run
this subquery on its own (see below), then the "order by id" is fine,
but all together it cannot run. Why is this?
When you have a subquery, the results are used as if they were a table. You can join on it, or query from it like you are, but the point is the order of that table has no effect on any thing else. The entry order of the underlying table is no guarantee that your query will come out in that order, unless you use an order by clause. And because you are doing a group by, that order means nothing anyway. Because the order of the subquery has no effect, SQL won't let you put it in.
If i perform a standard query in SQLite:
SELECT * FROM my_table
I get all records in my table as expected. If i perform following query:
SELECT *, 1 FROM my_table
I get all records as expected with rightmost column holding '1' in all records. But if i perform the query:
SELECT *, COUNT(*) FROM my_table
I get only ONE row (with rightmost column is a correct count).
Why is such results? I'm not very good in SQL, maybe such behavior is expected? It seems very strange and unlogical to me :(.
SELECT *, COUNT(*) FROM my_table is not what you want, and it's not really valid SQL, you have to group by all the columns that's not an aggregate.
You'd want something like
SELECT somecolumn,someothercolumn, COUNT(*)
FROM my_table
GROUP BY somecolumn,someothercolumn
If you want to count the number of records in your table, simply run:
SELECT COUNT(*) FROM your_table;
count(*) is an aggregate function. Aggregate functions need to be grouped for a meaningful results. You can read: count columns group by
If what you want is the total number of records in the table appended to each row you can do something like
SELECT *
FROM my_table
CROSS JOIN (SELECT COUNT(*) AS COUNT_OF_RECS_IN_MY_TABLE
FROM MY_TABLE)