Please concern following oracle beginner's case:
Table "X" contains customer data:
ID Variable_A Variable_B Variable_C Variable_D
--------------------------------------------------
1 100 null abc 2003/07/09
2 null 2 null null
Table "Dictionary" contains what we can regard as default values for customer data:
Variable_name Default_Value
----------------------------
Variable_A 50
Variable_B 0
Variable_C text
Variable_D sysdate
The goal is to examine the row in "X" by given ID and replace null values by the default values from "Dictionary". The concrete question is about the optimal solution because, for now my own solution lies in use of looping with MERGE INTO statement which is, I think, not optimal. Also it is necessary to use flexible code without being ought to change it when new column is added into "X".
The direct way is to use
update X set
variable_a = coalesce(variable_a, (select default_value from Dictionary where name = 'Variable_A')),
variable_b = coalesce(variable_b, (select default_value from Dictionary where name = 'Variable_B')),
... and so on ...
Generally it should be fast enough.
Since you don't know which fields of table X will be null, you should provide every row with every default value. And since each field of X may be a different data type, the Dictionary table should have each default value in a field of the appropriate type. Such a layout is shown in thisFiddle.
A query which shows each row of X fully populated with either the value in X or its default becomes relatively simple.
select ID,
nvl( Var_A, da.Int_Val ) Var_A,
nvl( Var_B, db.Int_Val ) Var_B,
nvl( Var_C, dc.Txt_Val ) Var_C,
nvl( Var_D, dd.Date_Val ) Var_D
from X
join Dict da
on da.Name = 'VA'
join Dict db
on db.Name = 'VB'
join Dict dc
on dc.Name = 'VC'
join Dict dd
on dd.Name = 'VD';
Turning this into an Update statement is a little more complicated but is simple enough once you've used it a few times:
update X
set (Var_A, Var_B, Var_C, Var_D) =(
select nvl( Var_A, da.Int_Val ),
nvl( Var_B, db.Int_Val ),
nvl( Var_C, dc.Txt_Val ),
nvl( Var_D, dd.Date_Val )
from X InnerX
join Dict da
on da.Name = 'VA'
join Dict db
on db.Name = 'VB'
join Dict dc
on dc.Name = 'VC'
join Dict dd
on dd.Name = 'VD'
where InnerX.ID = X.ID )
where exists(
select 1
from X
where Var_A is null
or Var_B is null
or Var_C is null
or Var_D is null );
There is a problem with this. The default for Date types is given as sysdate which means that it will show the date and time the default table was populated not the date and time the Update was performed. This, I assume, is not what you want. You could try to make this all work using dynamic sql, but that will be a lot more complicated. Much too complicated for what you want to do here.
I see only two realistic options: either store a meaningful date as the default (9999-12-31, for example) or just know that every default for a date type will be sysdate and use that in your updates. That would be accomplished in the above Update just by changing one line:
nvl( Var_D, sysdate )
and getting rid of the last join.
Related
I'm trying to replace a placeholder string inside a selection of 10 random records with a random string (a name) taken from another table, using only sqlite statements.
i've done a subquery in order to replace() of the placeholder with the results of a subquery. I thought that each subquery loaded a random name from the names table, but i've found that it's not the case and each placeholder is replaced with the same string.
select id, (replace (snippet, "%NAME%", (select
name from names
where gender = "male"
) )
) as snippet
from imagedata
where timestamp is not NULL
order by random()
limit 10
I was expecting for each row of the SELECT to have different random replacement every time the subquery is invoked.
hello i'm %NAME% and this is my house
This is the car of %NAME%, let me know what you think
instead each row has the same kind of replacement:
hello i'm david and this is my house
This is the car of david, let me know what you think
and so on...
I'm not sure it can be done inside sqlite or if i have to do it in php over two different database queries.
Thanks in advance!
Seems that random() in the subquery is only evaluated once.
Try this:
select
i.id,
replace(i.snippet, '%NAME%', n.name) snippet
from (
select
id,
snippet,
abs(random()) % (select count(*) from names where gender = 'male') + 1 num
from imagedata
where timestamp is not NULL
order by random() limit 10
) i inner join (
select
n.name,
(select count(*) from names where name < n.name and gender = 'male') + 1 num
from names n
where gender = 'male'
) n on n.num = i.num
I have the following columns (FirstCol, SecondCol, ThirdCol) in a sqlite3 db file:
1 Inside 100
1 Outside 200
2 Inside 46
2 Outside 68
First column has type INT, second has type TEXT and third one has type INT.
For each FirstCol value (in this case just 1 and 2) i need to obtain the result of the value associated with Outside/Inside, which is to say 200/100 where FirstCol=1 and 68/46 where FirstCol=2.
I don't mind whether this is done with a single query or by creating a new table, i just need that result.
Thanks.
You have to look up the values from different rows with correlated subqueries:
SELECT FirstCol,
(SELECT ThirdCol
FROM MyTable
WHERE FirstCol = T.FirstCol
AND SecondCol = 'Outside'
) /
(SELECT ThirdCol
FROM MyTable
WHERE FirstCol = T.FirstCol
AND SecondCol = 'Inside'
) AS Result
FROM (SELECT DISTINCT FirstCol
FROM MyTable) AS T;
I have an application which has data spread accross 2 tables.
There is a main table Main which has columns - Id , Name, Type.
Now there is a Sub Main table that has columns - MainId(FK), StartDate,Enddate,city
and this is a 1 to many relation (each main can have multiple entries in submain).
Now I want to display columns Main.Id, City( as comma seperated from various rows for that main item from submain), min of start date(from submain for that main item) and max of enddate( from sub main).
I thought of having a function but that will slow things up since there will be 100k records. Is there some other way of doing this. btw the application is in asp.net. Can we have a sql query or some linq kind of thing ?
This is off the top of my head, but firstly I would suggest you create a user defined function in sql to create the city comma separated list string that accepts #mainid, then does the following:
DECLARE #listStr VARCHAR(MAX)
SELECT #listStr = COALESCE(#listStr+',' , '') + city
FROM submain
WHERE mainid = #mainid
... and then return #listStr which will now be a comma separated list of cities. Let's say you call your function MainIDCityStringGet()
Then for your final result you can simply execute the following
select cts.mainid,
cts.cities,
sts.minstartdate,
sts.maxenddate
from ( select distinct mainid,
dbo.MainIDCityStringGet(mainid) as 'cities'
from submain) as cts
join
( select mainid,
min(startdate) as 'minstartdate',
max(enddate) as 'maxenddate'
from submain
group by mainid ) as sts on sts.mainid = cts.mainid
where startdate <is what you want it to be>
and enddate <is what you want it to be>
Depending on how exactly you would like to filter by startdate and enddate you may need to put the where filter within each subquery and in the second subquery in the join you may then need to use the HAVING grouped filter. You did not clearly state the nature of your filter.
I hope that helps.
This will of course be in stored procedure. May need some debugging.
An alternative to creating a stored procedure is performing the complex operations on the client side. (untested):
var result = (from main in context.Main
join sub in context.SubMain on main.Id equals sub.MainId into subs
let StartDate = subs.Min(s => s.StartDate)
let EndDate = subs.Max(s => s.EndDate)
let Cities = subs.Select(s => s.City).Distinct()
select new { main.Id, main.Name, main.Type, StartDate, EndDate, Cities })
.ToList()
.Select(x => new
{
x.Id,
x.Name,
x.Type,
x.StartDate,
x.EndDate,
Cities = string.Join(", ", x.Cities.ToArray())
})
.ToList();
I am unsure how well this is supported in other implimentations of SQL, but if you have SQL Server this works a charm for this type of scenario.
As a disclaimer I would like to add that I am not the originator of this technique. But I immediately thought of this question when I came across it.
Example:
For a table
Item ID Item Value Item Text
----------- ----------------- ---------------
1 2 A
1 2 B
1 6 C
2 2 D
2 4 A
3 7 B
3 1 D
If you want the following output, with the strings concatenated and the value summed.
Item ID Item Value Item Text
----------- ----------------- ---------------
1 10 A, B, C
2 6 D, A
3 8 B, D
The following avoids a multi-statement looping solution:
if object_id('Items') is not null
drop table Items
go
create table Items
( ItemId int identity(1,1),
ItemNo int not null,
ItemValue int not null,
ItemDesc nvarchar(500) )
insert Items
( ItemNo,
ItemValue,
ItemDesc )
values ( 1, 2, 'A'),
( 1, 2, 'B'),
( 1, 6, 'C'),
( 2, 2, 'D'),
( 2, 4, 'A'),
( 3, 7, 'B'),
( 3, 1, 'D')
select it1.ItemNo,
sum(it1.ItemValue) as ItemValues,
stuff((select ', ' + it2.ItemDesc --// Stuff is just used to remove the first 2 characters, instead of a substring.
from Items it2 with (nolock)
where it1.ItemNo = it2.ItemNo
for xml path(''), type).value('.','varchar(max)'), 1, 2, '') as ItemDescs --// Does the actual concatenation..
from Items it1 with (nolock)
group by it1.ItemNo
So you see all you need is a sub query in your select that retrieves a set of all the values you need to concatenate and then use the FOR XML PATH command in that sub query in a clever way. It does not matter where the values you need to concatenate comes from you just need to retrieve them using the sub query.
I'm trying to verify if data exists in two different tables in a single transaction. The reason for the single transaction is the database gets hit about 1-3 million times a day so adding anymore than 1 extra transaction would increase that number up to 9 million, and my poor little server needs a break :)
So I need to check if an ID exists in table X and table Y and return the results to my VB.net script so I can handle the outcome Ideally something like this would work
if exists (select id from X where id = #id)
print 'True,' else print 'False,'
if exists (select id from Y where id = #id)
print 'True' else print 'False'
Which gives me "True, True" if exists in both or "True, False" etc etc... But that only displays in SQL print and not actually returning it as an object/string or array values that I can use.
I'm open to any sort of solution of this nature that can give me two results from a single transaction and how to handle that response in vb. Thanks
SELECT
Case When EXISTS(SELECT 1 FROM X WHERE id = #id) Then 1 Else 0 End AS IsInX,
Case When EXISTS(SELECT 1 FROM Y WHERE id = #id) Then 1 Else 0 End AS IsInY
select (select COUNT(*) from X where id = #id) AS x_exists,
(select COUNT(*) from Y where id = #id) AS y_exists
This returns one data row with two fields, each containing either 0 or 1 (or more, if id is not unique).
CREATE PROCEDURE CheckIDOnTables(#ID int)
AS
BEGIN
DECLARE #X AS NVARCHAR(10)
DECLARE #Y AS NVARCHAR(10)
Set #X = 'False'
Set #Y = 'False'
if exists (select id from TableX where id = #ID)
Set #X = 'True'
if exists (select id from TableY where id = #ID)
Set #Y = 'True'
SELECT #X AS XExists, #Y AS YEsists
END
It will give you your desired results.
I have two tables(oracle):
(I have marked the primary keys with a star before the column name)
Table1 Columns are :
*date,
*code,
*symbol,
price,
weight
Table2 columns are :
*descriptionID
code
symbol
date
description
I need to find the below information using query,
For a given code and a symbol on a particular day,is there any description.
for example: code = "AA" and symbol = "TEST" on 2012-4-1 on Table 1 => is there atleast one row like ID=, code ="AA", symbol ="TEST" ,date = 2012-4-1 in table 2
I tried with the below query:
select * from Table1 t1 INNER JOIN
Table2 t2
on t1.code = t2.code and t1.symbol = t2.symbol and
TO_CHAR(t1.date, 'YYYY/MM/DD') = TO_CHAR(t1.date, 'YYYY/MM/DD')
But it doesnt give me output like:
code = AA, symbol = TEST, date 2012-4-1 => descrition count = 10
code = AA, symbol = TEST, date 2012-4-2 => descrition count = 5
code = BB, symbol = HELO, date 2012-4-1 => descrition count = 20
Can some one suggest me a query which can achieve the above output.
I don't see why you need the join:
SELECT count(*)
FROM Table2
WHERE code='AA'
AND symbol = 'TEST'
AND date = to_date('2012-04-01', 'yyyy-mm-dd')
UPDATE: (after reading your comment)
I still don't see why you need the join. Do you need some data from table1 ?
Anyway, if you want the count for all the (code,symbol,date)s then why not group by ?
As for the dates, better use trunc to get rid of the time parts.
So:
SELECT code, symbol, date, count(*)
FROM Table2
GROUP BY code, symbol, date
the Trunc() Method takes a String\Date input and Creates a DATE output that is in this Format: "DD\MM\YYYY".
So Its should do exactly what you want.