I have two tables, prisoner and person.
Prisoner:
prisoner_id
person_ssn
sentence_start
sentence_end
Person
first_name
last_name
person_ssn
If the sentence_start field is of type DATE, is it possible for me to calculate which month has had the most prisoners added and then show that month and how many there were?
You simple need to run a COUNT query and GROUP the results by month and possibly year:
SELECT YEAR(sentence_start) AS Y, MONTH(sentence_start) AS M, COUNT(*) AS C
FROM prisoner
GROUP BY YEAR(sentence_start), MONTH(sentence_start)
It is also possible to use the MySQL EXTRACT function to obtain same results MUCH faster:
SELECT EXTRACT(YEAR_MONTH FROM sentence_start) AS YM, COUNT(*) AS C
FROM prisoner
GROUP BY EXTRACT(YEAR_MONTH FROM sentence_start)
Related
How do I query the following:
For each customer, product and month, count the number of sales transactions that were between the previous and the following month's average sales quantities. For January and December, display NULL or 0.
Can only use: 5 aggregate functions (sum, count, avg, max & min)
This is the table reference:
create table sales
(
cust varchar(20),
prod varchar(20),
day integer,
month integer,
year integer,
state char(2),
quant integer,
date date
);
Schema:
Example of my Desired Result
I am stuck with the following codes. I'm having a hard time how to execute it.
SELECT cust, prod, month, COUNT(*) AS SALES_COUNT_BETWEEN_AVGS
FROM sales
I use MySQL. Please guide me thank you.
Maybe try a query like below
the first part is to calculate averages using group by
second part is to use to those averages in a JOIN twice for past month and future month
third part is WHERE clause in which we compare data. Note we have used greatest and least functions to determine min and max between two values from past and next month
Query
WITH T AS
(SELECT cust, prod, month, AVG(quant) AS avg_quantity
FROM sales
group by cust, prod, month
)
SELECT S.cust, S.prod, S.month, COUNT(1) AS Sales_count
FROM sales S
LEFT JOIN T T1
ON T1.cust=S.Cust AND
T1.prod=S.Prod AND
T1.Month=S.Month-1
LEFT JOIN T T2
ON T2.cust=S.Cust AND
T2.prod=S.Prod AND
T2.Month=S.Month+1
WHERE S.quant BETWEEN IFNULL(LEAST(T1.avg_quantity,T2.avg_quantity),0) AND IFNULL(GREATEST(T1.avg_quantity,T2.avg_quantity),0)
Question: Show the category of competitions that have always been hosted in the same country during May 2010. What is wrong with my query?
select Category
from competition
where Date >= '2010-01-01' and Date <= '2010-12-31'
group by Country, Category
having count(*) = (select count(*)
from competition
where Date >= '2010-01-01' and Date <= '2010-12-31'
group by Category)
You don't need two queries. Just use one query that checks that the count of countries is 1.
select category, count(DISTINCT country) AS country_count
from competition
where Date BETWEEN '2010-05-01' and '2010-05-31'
group by Category
HAVING country_count = 1
I also corrected the dates to be just May, not the whole year 2010.
Remove the GROUP BY if you that is making you return more than 1 row (in your HAVING CLAUSE. If you give me an example dataset and what you want I can help you more
I'd try something like this to start with:
SELECT COUNTRY
, CATEGORY
, COUNT(COUNTRY)
FROM COMPETITION
WHERE DATE BETWEEN '2010-04-30' AND '2010-06-01'
ORDER BY CATEGORY DESC, COUNT(COUNTRY) DESC
;
Your original query's date limits are just for the year of 2010 but you specified you only wanted May 2010. If the Date column is a date or datetime time you'll need to cast the string to the appropriate datatype.
Your question asked "always hosted by one country" - do you know that a competition is only going to be hosted by one country during that particular month? If you do, you're pretty much done. If you don't, however, then you need to clarify what your criteria really are
In oracle sql, how to get the count of newly added customers only for the month of april and may and make sure they werent there in the previous months
SELECT CUSTOMER ID , COUNT(*)
FROM TABLE
WHERE DATE BETWEEN '1-APR-2018' AND '31-MAY-2018' AND ...
If we give max (date) and min(date), we can compare the greater date to check if this customer is new , correct?
expected output is month count
april ---
may ---
should show the exact count how many new customers joined in these two months
One approach is to use aggregation:
select customer_id, min(date) as min_date
from t
group by customer_id
having min(date) >= date '2018-04-01 and
min(date) < date '2018-06-01';
This gets the list of customers (which your query seems to be doing). To get the count, just use count(*) and make this a subquery.
I just started to learn SQL and I have some queries to write to practise.
Can you help me and check it if it's correct?
I don't have an idea how to create three at the end
Let's assume that database is arbitrary. I just need to learn how to create those kind of queries to work on many diffrent databases.
-Specify the time from the system clock and the system clock date.
SELECT SYSDATETIME(),SYSDATETIMEOFFSET();
-Select employees that are in the age from 30 to 50 years.
SELECT * FROM employees
WHERE dateOfBirth BETWEEN DATE_SUB(NOW(), INTERVAL 30 YEAR)
AND DATE_SUB(date, INTERVAL 50 YEAR);
-Indicate in which department the employee works.
select employees.name, departments.name from employees where
employees.id_department=departments.id_department;
-Specify in what department the employee works and order in descending order and ascending order by name
select employees.name, departments.name from employees where
employees.id_department=departments.id_department ORDER BY Department DESC, Surname ASC;
-Specify in which department the employee works and order in descending order and ascending order by name limiting the number of tuples to chapters beginning with a or s.
-Is there a business department where no one is working?
View your net worker's salary, calculate your 18% tax rate and give you a tax deduction.
I'm new to this also. Would assume something like below:
select employees.name, departments.name from departments
Left Outer Join departments on departments.id_department = employees.id_department
WHERE employees.name IS NULL
How to optimize the below query:
I have two tables, 'calendar_table' and 'consumption', Here I use this query to calculate monthly consumption for each year.
The calendar table has day, month and year for years 2005 - 2009 and consumption table has billed consumption data for monthly bill cycle. This query will count the number of days for each bill and use that the find the consumption for each month.
SELECT id,
date_from as bill_start_date,
theYear as Year,
MONTHNAME(STR_TO_DATE(theMonth, '%m')) as month,
sum(DaysOnBill),
TotalDaysInTheMonth,
sum(perDayConsumption * DaysOnBill) as EstimatedConsumption
FROM
(
SELECT
id,
date_from,
theYear,
theMonth, # use theMonth for displaying the month as a number
COUNT(*) AS DaysOnBill,
TotalDaysInTheMonth,
perDayConsumption
FROM
(
SELECT
c.id,
c.date_from as date_from,
ct.dt,
y AS theYear,
month AS theMonth,
DAY(LAST_DAY(ct.dt)) as TotalDaysInTheMonth,
perDayConsumption
FROM
consumption AS c
INNER JOIN
calendar_table AS ct
ON ct.dt >= c.date_from
AND ct.dt<= c.date_to
) AS allDates
GROUP BY
id,
date_from,
theYear,
theMonth ) AS estimates
GROUP BY
id,
theYear,
theMonth;
It is taking around 1000 seconds to go through around 1 million records. Can something be done to make it faster?.
The query is a bit dubious pretending to do one grouping first and then building on that with another, which actually isn't the case.
First the bill gets joined with all its days. Then we group by bill plus month and year thus getting a monthly view on the data. This could be done in one pass, but the query is joining first and then using the result as a derived table which gets aggregated. At last the results are taken again and "another" group is built, which is actually the same as before (bill plus month and year) and some pseudo aggregations are done (e.g. sum(perDayConsumption * DaysOnBill) which is the same as perDayConsumption * DaysOnBill, as SUM sums one record only here).
This can simply written as:
SELECT
c.id,
c.date_from as bill_start_date,
ct.y AS Year,
MONTHNAME(STR_TO_DATE(ct.month, '%m')) as month,
COUNT(*) AS DaysOnBill,
DAY(LAST_DAY(ct.dt)) as TotalDaysInTheMonth,
SUM(c.perDayConsumption) as EstimatedConsumption
FROM consumption AS c
INNER JOIN calendar_table AS ct ON ct.dt BETWEEN c.date_from AND c.date_to
GROUP BY
c.id,
ct.y,
ct.month;
I don't know if this will be faster or if MySQL's optimizer doesn't see through your query itself and boils it down to this anyhow.