How to search max value from group in sql - sql

I am just learning some SQL, so I have a question.
-I have a table with name TABL
-a variable :ccname which has a value "Bottle"
The table is as follows:
+----------+---------+-------+--------+
| Name | Price | QTY | CODE |
+----------+---------+-------+--------+
| Rope | 3.6 | 35 | 236 |
| Chain | 2.8 | 15 | 237 |
| Paper | 1.6 | 45 | 124 |
| Bottle | 4.5 | 41 | 478 |
| Bottle | 1.8 | 12 | 123 |
| Computer | 1450.75 | 71 | 784 |
| Spoon | 0.7 | 10 | 412 |
| Bottle | 1.3 | 15 | 781 |
| Rope | 0.9 | 14 | 965 |
+----------+---------+-------+--------+
Now I want to find the CODE from the variable :ccname with the higher quantity! So I translated like this:
SELECT CODE
FROM TABL
GROUP BY :ccname
WHERE QTY=MAX(QTY)
In a perfect world that would turn as a result 478.
In the SQL world what should I write in order to get 478?

You probably want something like that:
SELECT code
FROM TABL
WHERE Name=:ccname
ORDER BY QTY DESC
LIMIT 1
The idea is we find all rows of the table whose Name column is the same as the contents of the variable :ccname, then order them by the quantity in descending order, and filally we select first one, which has to be the one with the largest quantity because they are sorted in descending order.

Try this
SELECT CODE
FROM TABLENAme
WHERE QTY = (SELECT MAX(QTY) FROM TablName WHERE Name = :ccname)

Use ORDER BY, a proper WHERE, and the something to limit the result set to one row:
SELECT CODE
FROM TABL
WHERE name = :ccname
ORDER BY QTY DESC
FETCH FIRST 1 ROW ONLY;
Note: Some databases spell the ANSI standard FETCH FIRST 1 ROW ONLY as LIMIT or as SELECT TOP 1.

Depending on your specific database, you can use one of the following options to restrict your result set to a single value after ordering your existing columns through an ORDER BY clause:
SELECT TOP 1
LIMIT 1
FETCH FIRST 1 ROW ONLY
Syntax Examples
SELECT TOP 1 Code
FROM TABL
WHERE Name = :ccname
ORDER BY QTY DESC
or
SELECT Code
FROM TABL
WHERE Name = :ccname
ORDER BY QTY DESC
LIMIT 1
or
SELECT CODE
FROM TABL
WHERE Name = :ccname
ORDER BY QTY DESC
FETCH FIRST 1 ROW ONLY;

Using join can also effectively solve the question:
Select t1.Code
From TABL As t1 Join (
Select Name, Max(table.QTY) as MaxQTY
From TABL
Where Name = :ccname
Group by Name
) As t2
Where t1.QTY = t2.MaxQTY And t1.Name = t2.Name
Explanation:
You first calculate the maximum value for "Bottle" using the subquery and then join the two tables to select corresponding row with MaxQTY and same name.

Related

tune query to avoid using aggregate function with order by

how can i rewrite the below query to avoid the use of aggegate function with order by :
select id from my_table where flow='REQ' and audit_time <= '04-Jul-2014' group by (id) order by min(audit_time);
since i have a large data set, the above query is causing performance issues.
below is a sample data:
pk | id | audit_time | flow
1 | 1 | 10-Jul-2014 | REQ
2 | 1 | 05-Jul-2014 | REQ
3 | 2 | 03-Jul-2014 | REQ
4 | 2 | 01-Jul-2014 | RES
5 | 1 | 04-Jul-2014 | RES
In output, i want to have the unique id list sorted by time.
You don't need group by id because id will be unique(It should be) and you are not joining any table
then you just have to order it by audit_time. And as you are not doing group by you don't need to use function in order by.
select id from my_table where flow='REQ' and audit_time <= '04-Jul-2014' order by audit_time;
If your ID is not unique and you want to order by minimum audit_time then your query is the only way(IMO).

SQL SELECT only rows where a max value is present, and the corresponding ID from another linked table

I have a simple Parts database which I'd like to use for calculating costs of assemblies, and I need to keep a cost history, so that I can update the costs for parts without the update affecting historic data.
So far I have the info stored in 2 tables:
tblPart:
PartID | PartName
1 | Foo
2 | Bar
3 | Foobar
tblPartCostHistory
PartCostHistoryID | PartID | Revision | Cost
1 | 1 | 1 | £1.00
2 | 1 | 2 | £1.20
3 | 2 | 1 | £3.00
4 | 3 | 1 | £2.20
5 | 3 | 2 | £2.05
What I want to end up with is just the PartID for each part, and the PartCostHistoryID where the revision number is highest, so this:
PartID | PartCostHistoryID
1 | 2
2 | 3
3 | 5
I've had a look at some of the other threads on here and I can't quite get it. I can manage to get the PartID along with the highest Revision number, but if I try to then do anything with the PartCostHistoryID I end up with multiple PartCostHistoryIDs per part.
I'm using MS Access 2007.
Many thanks.
Mihai's (very concise) answer will work assuming that the order of both
[PartCostHistoryID] and
[Revision] for each [PartID]
are always ascending.
A solution that does not rely on that assumption would be
SELECT
tblPartCostHistory.PartID,
tblPartCostHistory.PartCostHistoryID
FROM
tblPartCostHistory
INNER JOIN
(
SELECT
PartID,
MAX(Revision) AS MaxOfRevision
FROM tblPartCostHistory
GROUP BY PartID
) AS max
ON max.PartID = tblPartCostHistory.PartID
AND max.MaxOfRevision = tblPartCostHistory.Revision
SELECT PartID,MAX(PartCostHistoryID) FROM table GROUP BY PartID
Here is query
select PartCostHistoryId, PartId from tblCost
where PartCostHistoryId in
(select PartCostHistoryId from
(select * from tblCost as tbl order by Revision desc) as tbl1
group by PartId
)
Here is SQL Fiddle http://sqlfiddle.com/#!2/19c2d/12

Oracle sql Inner join first record in right table

my question is this:
I have two tables such as this:
username | portname | symbol | shares
---------+----------+--------+-------
phil | test | APL | 214
---------+----------+--------+--------
It has more records, but that's just an example. Then I have another table such as this, that has multiple records per symbol
symbol | high | low | timestamp
-------+------+-----+-----------
APL | 200 | 20 | *timestamp object
APL | 400 | 34 | *timestamp object
I want a table to be returned where I join the two, but only the first row from the second table is joined so something like this is returned:
symbol | high | low | timestamp
-------+------+-----+----------
APL | 400 | 34 | *timestamp object
So only one record from the right table is matched. I've tried alot of things but haven't gotten anything to work with group by's or distinct.
Thanks!
SELECT t1.symbol, t3.high, t3.low, t3.timestamp
FROM Table1 t1
JOIN (
SELECT inn.*
FROM (SELECT t2.*, (ROW_NUMBER() OVER(PARTITION BY symbol ORDER BY timestamp DESC)) As Rank
FROM Table2 t2) inn
WHERE inn.Rank=1
) t3
ON t1.symbol = t3.symbol;
See SQL Fiddle

SQL Query to select bottom 2 from each category

In Mysql, I want to select the bottom 2 items from each category
Category Value
1 1.3
1 4.8
1 3.7
1 1.6
2 9.5
2 9.9
2 9.2
2 10.3
3 4
3 8
3 16
Giving me:
Category Value
1 1.3
1 1.6
2 9.5
2 9.2
3 4
3 8
Before I migrated from sqlite3 I had to first select a lowest from each category, then excluding anything that joined to that, I had to again select the lowest from each category. Then anything equal to that new lowest or less in a category won. This would also pick more than 2 in case of a tie, which was annoying... It also had a really long runtime.
My ultimate goal is to count the number of times an individual is in one of the lowest 2 of a category (there is also a name field) and this is the one part I don't know how to do.
Thanks
SELECT c1.category, c1.value
FROM catvals c1
LEFT OUTER JOIN catvals c2
ON (c1.category = c2.category AND c1.value > c2.value)
GROUP BY c1.category, c1.value
HAVING COUNT(*) < 2;
Tested on MySQL 5.1.41 with your test data. Output:
+----------+-------+
| category | value |
+----------+-------+
| 1 | 1.30 |
| 1 | 1.60 |
| 2 | 9.20 |
| 2 | 9.50 |
| 3 | 4.00 |
| 3 | 8.00 |
+----------+-------+
(The extra decimal places are because I declared the value column as NUMERIC(9,2).)
Like other solutions, this produces more than 2 rows per category if there are ties. There are ways to construct the join condition to resolve that, but we'd need to use a primary key or unique key in your table, and we'd also have to know how you intend ties to be resolved.
You could try this:
SELECT * FROM (
SELECT c.*,
(SELECT COUNT(*)
FROM user_category c2
WHERE c2.category = c.category
AND c2.value < c.value) cnt
FROM user_category c ) uc
WHERE cnt < 2
It should give you the desired results, but check if performance is ok.
Here's a solution that handles duplicates properly. Table name is 'zzz' and columns are int and float
select
smallest.category category, min(smallest.value) value
from
zzz smallest
group by smallest.category
union
select
second_smallest.category category, min(second_smallest.value) value
from
zzz second_smallest
where
concat(second_smallest.category,'x',second_smallest.value)
not in ( -- recreate the results from the first half of the union
select concat(c.category,'x',min(c.value))
from zzz c
group by c.category
)
group by second_smallest.category
order by category
Caveats:
If there is only one value for a given category, then only that single entry is returned.
If there was a unique recordID for each row you wouldn't need all the concats to simulate a unique key.
Your mileage may vary,
--Mark
A union should work. I'm not sure of the performance compared to Peter's solution.
SELECT smallest.category, MIN(smallest.value)
FROM categories smallest
GROUP BY smallest.category
UNION
SELECT second_smallest.category, MIN(second_smallest.value)
FROM categories second_smallest
WHERE second_smallest.value > (SELECT MIN(smallest.value) FROM categories smallest WHERE second.category = second_smallest.category)
GROUP BY second_smallest.category
Here is a very generalized solution, that would work for selecting first n rows for each Category. This will work even if there are duplicates in value.
/* creating temporary variables */
mysql> set #cnt = 0;
mysql> set #trk = 0;
/* query */
mysql> select Category, Value
from (select *,
#cnt:=if(#trk = Category, #cnt+1, 0) cnt,
#trk:=Category
from user_categories
order by Category, Value ) c1
where c1.cnt < 2;
Here is the result.
+----------+-------+
| Category | Value |
+----------+-------+
| 1 | 1.3 |
| 1 | 1.6 |
| 2 | 9.2 |
| 2 | 9.5 |
| 3 | 4 |
| 3 | 8 |
+----------+-------+
This is tested on MySQL 5.0.88
Note that initial value of #trk variable should be not the least value of Category field.

Row Rank in a MySQL View

I need to create a view that automatically adds virtual row number in the result. the graph here is totally random all that I want to achieve is the last column to be created dynamically.
> +--------+------------+-----+
> | id | variety | num |
> +--------+------------+-----+
> | 234 | fuji | 1 |
> | 4356 | gala | 2 |
> | 343245 | limbertwig | 3 |
> | 224 | bing | 4 |
> | 4545 | chelan | 5 |
> | 3455 | navel | 6 |
> | 4534345| valencia | 7 |
> | 3451 | bartlett | 8 |
> | 3452 | bradford | 9 |
> +--------+------------+-----+
Query:
SELECT id,
variety,
SOMEFUNCTIONTHATWOULDGENERATETHIS() AS num
FROM mytable
Use:
SELECT t.id,
t.variety,
(SELECT COUNT(*) FROM TABLE WHERE id < t.id) +1 AS NUM
FROM TABLE t
It's not an ideal manner of doing this, because the query for the num value will execute for every row returned. A better idea would be to create a NUMBERS table, with a single column containing a number starting at one that increments to an outrageously large number, and then join & reference the NUMBERS table in a manner similar to the variable example that follows.
MySQL Ranking, or Lack Thereof
You can define a variable in order to get psuedo row number functionality, because MySQL doesn't have any ranking functions:
SELECT t.id,
t.variety,
#rownum := #rownum + 1 AS num
FROM TABLE t,
(SELECT #rownum := 0) r
The SELECT #rownum := 0 defines the variable, and sets it to zero.
The r is a subquery/table alias, because you'll get an error in MySQL if you don't define an alias for a subquery, even if you don't use it.
Can't Use A Variable in a MySQL View
If you do, you'll get the 1351 error, because you can't use a variable in a view due to design. The bug/feature behavior is documented here.
Oracle has a rowid pseudo-column. In MySQL, you might have to go ugly:
SELECT id,
variety,
1 + (SELECT COUNT(*) FROM tbl WHERE t.id < id) as num
FROM tbl
This query is off the top of my head and untested, so take it with a grain of salt. Also, it assumes that you want to number the rows according to some sort criteria (id in this case), rather than the arbitrary numbering shown in the question.