Tables to Join
I attached an image explaining issues that I currently face at the moment. I was looking for a way to join two tables. Where first table has a relationship to the previous table that its foreign key in first table. The second table also have foreign key of the first table.
What I want is to output the information is a list of the records of the second table that has the foreign key of the first table as well as the foreign key of the previous table that only linked to first table only.
Thank you very much for your support and I am looking forward to hear from you all soon
If you are using SQL Server, try creating a view function. You can easily add tables and view the sql results after you connect all of them. It also has a built in function that will automatically creates the sql queries corresponding to your created view function.
May you give this a try?
select a.clm,b.clm,c.clm from tableA as a
inner join table b as b on a.clm = b.clm
inner join table c as c on c.clm = b.clm
where clm is the column that could be joined from table A as well as table B as well as table c
If ever, kindly give us a bit more info about
Related
I am very new to SQL coding, I am using SQL Developer as the software to code.
I have a question, which I have tried to google and figure out but am having trouble.
I create a table called patvisit (patient visit) from two datasets Patient and visit. So I run the code below to create the new table patvisit. However, how do I add new columns with values into patvisit table without dropping the table and rerunning it. For example, I run the code below and create the table patvisit after I make the table I forget that I also wanted to add address that was in the patient table. Now what I would do is drop the patvisit table and then re-run the below code and add another column a.address. But is there a way to use the ALTER or ADD rules to be able to add a new column to an existing table? I tried looking for example codes online but I don't seem to get it. would appreciate any assistance/advise.
create table pativisit as
select distinct a.patientId, b.visit_no, b.visit_code, a.admit_date, a.discharge_date
from Patient a
inner join visit b
on a.visit_no=b.visit_no;
Thank you!
Check out this link on using the SQL ALTER TABLEstatement to ad a column:
https://www.w3schools.com/sql/sql_alter.asp
I have a dimension table in my database that has grown too large. With that I mean that is has too many records - over a million - because it grew at the same pace as the linked facts. This is mostly due to a bad design, and I'm trying to clean it up.
One of the things I try to do is to remove dimension records which are no longer used. The fact tables are regularly maintained and old snapshots are removed. Because the dimensions were not maintained like that, there are many rows in the table whose primary key value no longer appears in any of the linked fact tables anymore.
All the fact tables have foreign key constraints.
Is there a way to locate table rows whose primary key value no longer appears in any of the tables which are linked with a foreign key constraint?
I tried writing a script to track this. Basically this:
select key from dimension
where not exists (select 1 from fact1 where fk = pk)
and not exists (select 1 from fact2 where fk = pk)
and not exists (select 1 from fact3 where fk = pk)
But with a lot of linked tables this query dies after some time - at least, my management studio crashed. So I'm not sure if there are any other options.
we had to do something similar to this at one of my clients. The query, like yours with "not exists.... and not exists.... and not exists...." was taking ~22 hours to run before we change our strategy to handle this in ~20 minutes.
As Nsousa suggest, you have to split the query so SQL Server doesn't have to handle all data in one shot, having to unnecessarily use tempdb and all other things.
First, create new table with all keys in it. The reason to create this table is to not have to read the full table scan for every query, having more keys on a 8k page and to deal with a smaller and smaller set of keys after each delete.
create table DimensionkeysToDelete (Dimkey char(32) primary key nonclustered);
insert into DimensionkeysToDelete
select key from dimension order by key;
Then, instead of deleting unused key, delete the keys that exists in facts table, beginning with the fact table that has the least numbers of rows.
Make sure facts table have proper indexing for performance.
delete from DimensionkeysToDelete
from DimensionkeysToDelete d
inner join fact1 on f.fk = d.Dimkey;
delete from DimensionkeysToDelete
from DimensionkeysToDelete d
inner join fact2 on f.fk = d.Dimkey;
delete from DimensionkeysToDelete
from DimensionkeysToDelete d
inner join fact3 on f.fk = d.Dimkey;
Once all facts tables done, only unused keys remains in DimensionkeysToDelete. To answers your question, just perform a select on this table to get all unused key for that particular dimension, or join it with the dimension to get data.
But, from what I understand of your needs for cleaning up you warehouse, use this table to delete from the orignal dimension table. At this step, you might also want take some action for auditing purposes (ie: insert in an audit table 'Key ' + key + ' deleted on + convert(datetime, getdate(),121) + ' by script X'.... )
I think this can be optimize, take a look at the execution plan, but my client was happy with it so we didn't have to put much effort in it.
You may want to split that into different queries. Check unused rows in fact1, then on fact2, etc, individually. Then intersect all those results to get to the rows that are unused in all fact tables.
I would also suggest a left outer join instead of nested queries, counting rows in the fact table for each pk, and filter out from the resultset those that have a non zero count.
Your query will struggle as it’ll scan every fact table at the same time.
When I add news rows using the Insert into select code, the new rows get added randomly in between the already existing rows, instead of getting added to the end of the table.
I'm using, Insert into Table1 (Name1) select Name from Table2.
SQL tables are modeled after unordered sets, and hence you should not assume that there is any order to your data in the table. The only order which exists is what you specify when you query using ORDER BY, e.g.
SELECT Name1
FROM Table1
ORDER BY Name1
An index can also be thought of a way of ordering your records, but these two are mostly distinct entities from your actual table.
I agree with Tim's answer. But if you still want the data inserted in the way you want, then you can try to add the primary key yourself which is incremental (like 1,2,3 ... or 10,20,30 ...).
Although I don't recommend it, but I think following can help you if you don't want to handle the primary key yourself.
How do I add a auto_increment primary key in SQL Server database?
I have a script for microsoft sql server database which has hundreds of tables and tables contains data as well. This is the database of a web application.what I want to do is to delete the previous records and reset the primary key to 1 or 0.
I have tried
`DBCC CHECKIDENT ('dbo.tbl',RESEED,0); `
but it does not work for me as in most of the tables the primary key is not identity.
I can not truncate the table as its primary key is being used as FK in many other tables.
I have also tried to add the identity specification in the primary key of the table and run the checkident query and then changing it back to non-identity spec, but after adding the record again it starts from where it left.
Making changes in the code is not an option for me.
please help.
According with your question I am not sure about the main objective, Why? If you need truncate a lot of tables and change their structures to have an Identity property why you can't disabled the FK? . In the past I have used an standard process for rebuild a table and migrate all the information, this represent a group of steps, I would try to help you but you should follow the next steps.
Steps:
1) Disable FK for alter the structure of your tables. You can get the solution for this task in the next link:
Temporarily disable all foreign key constraints
2) Alter the table with the new property Identity, this is a classic process of ALTER TABLE xxxxxx.
3) Execute the syntax that previously posted :
DBCC CHECKIDENT ('dbo.tbl',RESEED,0);
Try to follow this path and if you have any problem only ask us.
You can not truncate table that have relation. You shoud remove relation firstly.
My understanding of this question:
You have a database with tables that you want to empty and next have them use primary key values starting at 0 or 1.
Some of these tables use an identity value and you already have a solution for those (you know you can find out which columns have an identity by using the sys.columns view? Look for the is_identity column).
Some tables do not use an identity but get their pk values from an unknown source, which we can't modify.
The only solution I see, is creating an after insert trigger (or modifying) on those tables that subtracts from the new pk value.
E.g.: your "hidden generator" will generate a next value 5254, but you want the next pk value to become one:
CREATE TRIGGER trg_sometable_ai
ON sometable
AFTER INSERT
AS
BEGIN
UPDATE st
SET st.pk_col = st.pk_col - 5253
FROM sometable AS st
INNER JOIN INSERTED AS i
ON i.pk_col = th.pk_col
END
You'll have to determine the next value and thus the "subtract value" for each table.
If the code also inserts child records into tables with a foreign key to this table, and uses the previously generated value, you have to modify those triggers as well...
This is a "last resort" solution and something I would recommend against in any scenario that has other options. Manipulating primary key values is generally not a good idea.
I need to define a one-to-one relationship, and can't seem to find the proper way of doing it in SQL Server.
Why a one-to-one relationship you ask?
I am using WCF as a DAL (Linq) and I have a table containing a BLOB column. The BLOB hardly ever changes and it would be a waste of bandwidth to transfer it across every time a query is made.
I had a look at this solution, and though it seems like a great idea, I can just see Linq having a little hissy fit when trying to implement this approach.
Any ideas?
One-to-one is actually frequently used in super-type/subtype relationship. In the child table, the primary key also serves as the foreign key to the parent table. Here is an example:
CREATE TABLE Organization
(
ID int PRIMARY KEY,
Name varchar(200),
Address varchar(200),
Phone varchar(12)
)
GO
CREATE TABLE Customer
(
ID int PRIMARY KEY,
AccountManager varchar(100)
)
GO
ALTER TABLE Customer
ADD FOREIGN KEY (ID) REFERENCES Organization(ID)
ON DELETE CASCADE
ON UPDATE CASCADE
GO
Why not make the foreign key of each table unique?
there is no such thing as an explicit one-to-one relationship.
But, by the fact that tbl1.id and tbl2.id are primary keys and tbl2.id is a foreign key referenceing tbl1.id, you have created an implicit 1:0..1 relationship.
Put 1:1 related items into the same row in the same table. That's where "relation" in "relational database" comes from - related things go into the same row.
If you want to reduce size of data traveling over the wire consider either projecting only the needed columns:
SELECT c1, c2, c3 FROM t1
or create a view that only projects relevant columns and use that view when needed:
CREATE VIEW V1 AS SELECT c1, c2, c3 FROM t1
SELECT * FROM t1
UPDATE v1 SET c1=5 WHERE c2=7
Note that BLOBs are stored off-row in SQL Server so you are not saving much disk IO by vertically-partitioning your data. If these were non-BLOB columns you may benefit form vertical partitioning as you described because you will do less disk IO to scan the base table.
How about this. Link the primary key in the first table to the primary key in the second table.
Tab1.ID (PK) <-> Tab2.ID (PK)
My problem was I have a 2 stage process with mandatory fields in both. The whole process could be classed as one episode (put in the same table) but there is an initial stage and final stage.
In my opinion, a better solution for not reading the BLOB with the LINQ query would be to create a view on the table that contains all the column except for the BLOB ones.
You can then create an EF entity based on the view.