I'm currently studying SQL language in Oracle.
After making very simple STUDENT table, I thought about how to make character sequence in ID field.
For example, if STUDENT table has 6 rows, I want the ID field to be inserted by 'a','b','c'...'f' characters respectively. And another condition is that the ID sequence should be ordered by age in ascending order.
The below explanation is about STUDENT table description and current inserted value (ID field is currently empty).
NAME AGE GRADE ID
hi 15 1
dui 12 2
giyu 16 3
hero 27 4
power 55 3
rai 37 4
///////////////////////////////////////////////////////////////////////////////////////////////////////
DESC STUDENT
NAME VARCHAR2(20)
AGE NUMBER(5)
GRADE NUMBER
ID VARCHAR2(12)
I hope many brilliant ideas come up here =)
until now, this is very easy to come up with making table ordered by age.
but inserting character sequence respectively is ... well .. idea doesn't come up now. And this is not homework. i just want to practice sql language.
update tableX X
set ID=(
select ID from (
select rowid as rid,
chr(mod((row_number() over (order by age))-1,26)+97) as ID
from tableX T
)
where rid=X.rowid
)
Required order of the ID set in the over(order by ) clause. Function row_number() gets sequence number of rows in given order. mod() gets remainder of the division (for 26 chars only). chr() get char by the ascii code.
Related
All first name should randomly match with each other and when I tried to run query again the First Name should be match with others name. Not the match with FIRST time match.
For example I have 6 records in one table ...
First name column looks like:
JHON
LEE
SAM
HARRY
JIM
KRUK
So I want result like
First name1 First name2
Jhon. Harry
LEE. KRUK
HARRY SAM
The simplest solution is to first randomly sort the records, then calculate the grouping and a sequence number within the group and then finally select out the groups as rows.
You can follow along with the logic in this fiddle: https://dbfiddle.uk/9JlK59w4
DECLARE #Sorted TABLE
(
Id INT PRIMARY KEY,
FirstName varchar(30),
RowNum INT IDENTITY(1,1)
);
INSERT INTO #Sorted (Id, FirstName)
SELECT Id, FirstName
FROM People
ORDER BY NEWID();
WITH Pairs as
(
SELECT *
, (RowNum+1)/2 as PairNum
, RowNum % 2 as Ordinal
FROM #Sorted
)
SELECT
Person1.FirstName as [First name1], Person2.FirstName as [First name2]
FROM Pairs Person1
LEFT JOIN Pairs Person2 ON Person1.PairNum = Person2.PairNum AND Person2.Ordinal = 1
WHERE Person1.Ordinal = 0
ORDER BY Person1.PairNum
ORDER BY NEWID() is used here to randomly sort the records. Note that it is indeterminate and will return a new value with each execution. It's not very efficient, but is suitable for our requirement.
You can't easily use CTE's for producing lists of randomly sorted records because the result of a CTE is not cached. Each time the CTE is referenced in the subsequent logic can result in re-evaluating the expression. Run this fiddle a few times and watch how it often allocates the names incorrectly: https://dbfiddle.uk/rpPdkkAG
Due to the volatility of NEWID() this example stores the results in a table valued variable. For a very large list of records a temporary table might be more efficient.
PairNum uses the simple divide by n logic to assign a group number with a length of n
It is necessary to add 1 to the RowNum because the integer math will round down, see this in action in the fiddle.
Ordinal uses the modulo on the RowNumber and is a value we can use to differentiate between Person 1 and Person 2 in the pair. This helps us keep the rest of the logic determinate.
In the final SELECT we select first from the Pairs that have an Ordinal of 0, then we join on the Pairs that have an Ordinal of 1 matching by the PairNum
You can see in the fiddle I added a solution using groups of 3 to show how this can be easily extended to larger groupings.
Can anyone help? My trouble is that people might have the same id or different and have different name spellings. If I group by id (which is not the primary key) I get a different amount of rows than if I group by ID and name. How do I just group by ID, while still having the ID and Name in the select?
Create Table Client(ID Int, Name Varchar(15))
Insert Into Client VALUES(11,'Batman'),(22,'Batman'),(33,'Robin'),(44,'Joker'),(44,'The Joker'),(33,'Robin')
Select Count(ID) From Client
Select * From Client
--This returns 4 rows as it should
Select Count (ID)
From Client
Group By ID
--This returns 5 rows because Joker and The Joker have different names, but the same ID. I want to count by ID and not the name, since so many have typos.
Select Count (ID), [Name] , ID
From Client
Group By ID, [Name]
How do I do this and have it work?
Select Count (ID), [Name] , ID
From Client
Group By ID --<< Always throws and error unless I include Name, which
--returns too many rows.
It should return
Count Name ID
1 Batman 11
1 Batman 22
2 Joker 44 --<< Correct
2 Robin 33
And not
Count Name ID
1 Batman 11
1 Batman 22
2 Robin 33
1 Joker 44 --Wrong
1 The Joker 44 --Wrong
using select count(*) from ClientLog will tell you exactly how many records there are in your table. If your ID field is the primary key, then select count(ID) from ClientLog should return the same number.
Your first query is a little confusing, because you're grouping by ID but not displaying the ID. So you're likely getting a row for each record, where the row value is 1.
Your 2nd query is also a bit confusing, because there's no aggregation happening (since your ID field is unique).
What specifically are you trying to obtain in your query (if anything besides just how many records you have in your table)?
I'm reading about 1 of the oracle pseudocolumns i.e
ROWNUM: which return number indicating the order in which oracle return the row.
I have encountered some behavior here,
Example used
1. Create Script:
CREATE TABLE CUSTOMERS(
ID INT NOT NULL,
NAME VARCHAR (20) NOT NULL,
AGE INT NOT NULL,
ADDRESS CHAR (25) ,
SALARY DECIMAL (18, 2),
PRIMARY KEY (ID)
);
2 Insert Script:
INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (2, 'Max', 22, 'India', 4500.00 );
INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (1, 'Maths', 22, 'US', 4500.00 );
select * from CUSTOMERS; executed in the same order as inserted above,
ID NAME AGE ADDRESS SALARY
------ ---- --- ------- ------
2 Max 22 India 4500.00
1 Math 22 US 4500.00
Here if I run the select query,
select
rownum,
customers.ID
from customers;
I get below output:
ROWNUW ID
------ --
1 1
2 2
Here ID = 2 is inserted first but oracle returns in the 2nd row,
But if you include any other column from a table with ROWNUM and PK like
select
rownum,
customers.ID,customers.Name
from customers;
I get correct output (Correct inserted order) :
ROWNUW ID NAME
------ -- ----
1 2 Max
2 1 Math
If run query without Name column i.e only ROWNUW (pseudocolumns) and PK (table column)
We get this,
ROWNUW ID
------ --
1 1
2 2
My Question is Why is that ID=2 is not first returned row.
if I query any table column with ROWNUM, I get the result back based on insertion order.
Example below
select
rownum,
(NAME / AGE / ADDRESS SALARY) any one of these columns
From CUSTOMERS
But if use ROWNUM with ID (Primary Key column) insertion order is not working. why is this behavior with the only Primary Key column?
ROWNUM values depends on how oracle access the resultset. Once resultset is fetched, rownum is assigned to the rows.
As there is no guarantee in what order the data is returned, there is no guarantee in what order rownum is assigned.
Maybe if you try running both of your queries without rownum, you might get the rows swapped as you showed, or they might not.
Rownum will always be in order of 1,2,3,4 .. no matter what you are getting in result set. It is always calculated after result set is returned from query.
Now, you have ID column as PRIMARY KEY which makes it eligible for default clustered index creation in database. So when you select only PRIMARY column, it will be sorted as it was stored in DB that way. Index created as a result of PRIMARY key creation is sorted in ASC which is default.
Here if you select only PRIMARY KEY column i.e. "ID", Database is returning it in sorted order and ROWNUM is writing 1 & 2 to it.
But if you are selecting some extra non-PRIMARY KEY as well then it is totally upto oracle, whichever way it finds data faster. Sometimes it will return data from cache memory. If not it will read disk and fetch data. While reading datafile, there are multiple things which will differ machine to machine i.e is your table partitioned? is your table sharing tablespace ? what organization you are using in table ? blah blah....
Bottom line is, don't trust ROWNUM. It gives 1,2,3.. after you have applied your brain to the query.
I am trying to count the number records based on the text in the table
Am having Table Structure Like this
SN_ID NUMBER
PERSON_ID NUMBER
NOTICE_TYPE VARCHAR2
and the contents of the table like this
SN_ID PERSON_ID NOTICE_TYPE
-------+-----------+--------------
1 5 Appreciation
2 5 Warning
3 1 Warning
4 5 Incident
5 2 Warning
6 5 Warning
I want to count the number Appreciation, Warning and Incident records for the person with an Id = 5
select Notice_type, count(*) from [Table]
where person_id=5
group by notice_type
SELECT NOTICE_TYPE, count(SN_ID)
FROM [Table]
WHERE PERSON_ID = 5
GROUP BY NOTICE_TYPE
This is slightly different from MikkaRin answer.
Difference is count(SN_ID). I took only one column here. Because it is more optimized method than taking whole column into the count() function. This will affected to large queries.
p.s. actually we should get the primary key into the count() function. Here SN_ID look like the PK.
I have a SQL Server 2005 database I'm working with. For the query I am using, I want to add a custom column that can start at any number and increment based on the row entry number.
For example, I start at number 10. Each row in my results will have an incrementing number 10, 11, 12, etc..
This is an example of the SELECT statement I would be using.
int customVal = 10;
SELECT
ID, customVal++
FROM myTable
The format of the above is clearly wrong, but it is conceptually what I am looking for.
RESULTS:
ID CustomColumn
-------------------
1 10
2 11
3 12
4 13
How can I go about implementing this kind functionality?
I cannot find any reference to incrementing variables within results. Is this the case?
EDIT: The customVal number will be pulled from another table. I.e. probably do a Select statement into the customVal variable. You cannot assume the the ID column will be any usable values.
The CustomColumn will be auto-incrementing starting at the customVal.
Use the ROW_NUMBER ranking function - http://technet.microsoft.com/en-us/library/ms186734.aspx
DECLARE #Offset INT = 9
SELECT
ID
, ROW_NUMBER() OVER (ORDER BY ID) + #Offset
FROM
Table