Alternative for a loop - mysql

I am trying to generate a simple report that will display the number of customers owning number of distinct brands. The following query I wrote generates the desired numbers one at a time. I tried writing a loop and it takes forever. Is there an alternative?
SELECT COUNT(DISTINCT customer_id)
FROM
(
SELECT customer_id,COUNT(DISTINCT brand) AS no_of_customers
FROM table_A
WHERE brand_id != 10
GROUP BY customer_id
HAVING COUNT(DISTINCT brand) =1
ORDER BY customer_id) as t1;
What this does is to give me a count of customers with a total count of distinct brands =1. I change the count of brands to 2,3 and so on. Please let me know if there is a way to automate this.
Thanks a lot.


Use a second level of GROUP BY to get them all in one query, rather than looping.
SELECT no_of_brands, COUNT(*) no_of_customers
FROM (SELECT customer_id, COUNT(DISTINCT brand) no_of_brands
FROM Table_A
WHERE brand_id != 10
GROUP BY customer_id) x
GROUP BY no_of_brands
You also don't need DISTINCT in your outer query, since the inner query's grouping guarantees that the customer IDs will be distinct.

Related

Count Distinct on multiple values within same column in SQL Aggregation

Objective:
I wanted to show the number of distinct IDs for any combination selected.
In the below example, I have data at a granular level: ID level data.
I wanted to show the number of distinct IDs for each combination.
For this, I use count distinct which will give me '1' for the below combinations.
But let's say if I wanted to find the number of IDs who made both E-commerce and Face to face transactions, in that case, if I just use this data, I would be showing the sum of E-comm and Face to face and the result would be '2' instead of '1'.
And this is not limited to Ecom/Face to face. I wanted to apply the same logic for all columns.
Please let me know if you have any other alternative approach to address this issue.

First aggregate in your table to get the distinct ids for each TranType:
SELECT TranType, COUNT(DISTINCT id) counter_distinct
FROM tablename
GROUP BY TranType
and then join to the table:
SELECT t.*, g.counter_distinct
FROM tablename t
INNER JOIN (
SELECT TranType, COUNT(DISTINCT id) counter_distinct
FROM tablename
GROUP BY TranType
) g ON g.TranType = t.TranType
Or use a correlated subquery:
SELECT t1.*,
(SELECT COUNT(DISTINCT t2.id) FROM tablename t2 WHERE t2.TranType = t1.TranType) counter_distinct
FROM tablename t1

But let's say if I wanted to find the number of IDs who made both E-commerce and Face to face transactions, in
You can get the list of ids using:
select id
from t
where tran_type in ('Ecomm', 'Face to face')
group by id
having count(distinct tran_type) = 2;
You can get the count using a subquery:
select count(*)
from (select id
from t
where tran_type in ('Ecomm', 'Face to face')
group by id
having count(distinct tran_type) = 2
) i;

Select entries appearing in all results from another query

I have a single table.
This table has 2 fields, product IDs and Store IDs. The same product ID can exist with many different Store IDs.
I need to find the products (if any) that are common across all the stores.
I'm having difficulty constructing the correct query, any advice?

You can check distinct store ids count with product id. If distinct Store ids count equal to total stores that will be the product ids you want.
SELECT productID, count(DISTINCT StoreID) as stroes FROM [Table name] GROUP BY productID
HAVING COUNT(DISTINCT StoreID) = (SELECT COUNT(DISTINCT StoreID) FROM [Table name] );

I'm sure you'll get many better answers, but it sounds like you are wanting the reverse of the distinct clause, not sure if this will work though:
SELECT NOT DISTINCT [Product_ID]
FROM TABLENAMEHERE

You could sue count(distinct productID)
select productID
from my_table
group by productID
having count(distinct productID) = (
select count(distinct store)
from my_table )

Find duplicate records with different values

I know how to query to find records with duplicate records based on a field or fields e.g.
Select Customer,Count(*) from Table1 group by Customer,Month having count(*)>1
which would give me a list of all customers who ordered more than once in a given month.
However from that select I'd like to:
Refine the group to show only dupes where the product is DIFFERENT. I know if I wanted to do the same I'd simple add to group by ',Product' but in my case it is Product != Product and I'm not sure how to indicate that in the group
Instead of getting a list of just which Customers ordered more than one product in a given month a list of all those orders. In other words instead of this type of list from the group:
Bob,December
Mary,June
I am trying to return:
Bob,Widget,December
Bob,Pipes,December
Mary,Books,June
Mary,Cars,June

If product field is in the same table, then you can use count with distinct on the product field to get the number of distinct products:
Select Customer, Month, Count(distinct product)
from Table1
group by Customer, Month
having count(distinct product)>1
If you want to know what they ordered, then join it back as a subquery to your main table:
select distinct t1.customer, t1.month, t1.product from table1 t1
inner join
(Select Customer, Month, Count(distinct product)
from Table1
group by Customer, Month
having count(distinct product)>1
) t2 on t1.customer=t2.customer and t1.month=t2.month
The distinct in the outer select depends on your exact needs.

Maximum and Minimum on nested subquery

I'm working on Libray Management System. I've a few tables among which i have Member_master and Book_issue_details tables.
Book_issue_tables contains details like book_id, member_id and book issue date, return date, etc.
I need to retrieve name and count of books for those members who have been issued maximum and minimum number of books.
I'm able to retrieve name and number of books with a simple group by query. But i'm getting clueless over how to retrieve max and min over the retrieved resultset. Correlated subquery?

You can add a HAVING clause that filters the groups using Subqueries with ALL:
SELECT name, COUNT(*)
FROM Book_issue_details
GROUP BY name
HAVING COUNT(*) <= ALL (SELECT COUNT(*) FROM Book_issue_details GROUP BY name)
OR COUNT(*) >= ALL (SELECT COUNT(*) FROM Book_issue_details GROUP BY name)

Mysql query to find distinct rows shows incorrect result

I wish to find the total number of distinct records in a table.
I have a table with the following columns
id, name, product, rating, manufacturer price
This has around 128 rows with some duplicates based on different column names.
I only want to select distinct rows:
select distinct name, product, rating, maufacturer, price from table
This returns 47 rows
For pagination purposes, I need to find the total number of distinct records, so I have another satatement:
select distinct count(name), product, rating, maufacturer, price from table
But this returns 128 instead of 47.
How can I get the total number of distinct rows? Any help will be much appreciated. Thanks

You have the distinct and count reversed.
SELECT COUNT(DISTINCT column_name) FROM table_name
Also, I would drop the extra fields when counting, your results will be unexpected for those other fields.

It is not quite clear if you want to get the count in the SAME query with the results or if you want to run a different query. Here go both solutions. In the result as a new column:
select distinct name, product, rating, manufacturer, price, (
select count(*) from (
select distinct name, product, rating, manufacturer, price from table1
) as resultCount) as resultCount
from table1
Notice the previous solution will repeat the count(*) for each row, which is not very efficient, not even visually appealing. Try running two queries one getting the actual data and the other one to get the amount of records in the table that match that data:
select distinct name, product, rating, manufacturer, price from table1
select count(*) from (
select distinct name, product, rating, manufacturer, price from table1
) as result
Hope this helps

Try adding GROUP BY name, product, rating, maufacturer, price clause

It would require running your actual query TWICE... an INNER for distinct and then get the count of those as a single row returned, and then join that to the original select distinct...
select distinct
t1.product,
t1.rating,
t1.maufacturer,
t1.price,
JustTheCount.DistCnt
from
table t1,
( select count(*) as DistCnt
from ( select distinct
t2.product,
t2.rating,
t2.maufacturer,
t2.price
from
table t2 )
) JustTheCount

In the following query, you're getting rows with distinct names since the DISTINCT clause precedes the name column:
SELECT DISTINCT name, product, rating, maufacturer, price FROM table
However, to get the count of the same records, use the following format:
SELECT COUNT(DISTINCT name) FROM table
Notice that DISTINCT goes inside of the COUNT function so that you're counting the distinct names. You probably don't want to include the other columns in the count query because they will be a random sample from the set. Of course, if you want a random sample, then include them.
Most applications will run the count query first, followed by the query to return the results. Also keep in mind that COUNT(*) is only an estimate, and the value may differ from the actual number of records returned.
SELECT DISTINCT COUNT(name), product FROM table isn't even a valid query in MySQL 4.x. You can't mix aggregate and non-aggregate columns. IN 5.x, it'll run, but the values for the non aggregate columns will be a random sample from the set.

At the risk of sparking some flames here.. you could always use:
SQL_CALC_FOUND_ROWS as the first part of your SQL. This is very mysql specific though.
http://dev.mysql.com/doc/refman/5.0/en/information-functions.html
mysql> SELECT SQL_CALC_FOUND_ROWS * FROM tbl_name
-> WHERE id > 100 LIMIT 10;
mysql> SELECT FOUND_ROWS();