I have a linked Oracle 11g server in Microsoft SQL Server 2012.
I am trying to retrieve a large linked dataset from Oracle and so to limit it I want to just get the first 100 records.
In SQL Server it's simply
select top 100 from ....
In Oracle the syntax is
...where rownum <= 100 order by rownum
As soon as my SQL Server 2012 query has more than two joins in it my
select top 100
causes the following error
OLE DB provider "OraOLEDB.Oracle" for linked server "BIS" returned message "ORA-01403: no data found
Msg 7346, Level 16, State 2, Line 1
Cannot get the data of the row from the OLE DB provider "OraOLEDB.Oracle" for linked server "BIS".
If I take top 100 out, it works but drags too much data over our network. Plus I also need to add a considerable number of joins to the select statement to the 3 I already have before I'm finished.
How can I join a large number of tables in a select statement but only return the first 100 records using T-SQL syntax on my SQL Server 2012 and retrieve these records from Oracle?
Depending on the logic you want, you could pull the top 100 rows into a temporary table and then use that. I say "depending" because you may want your final query to have 100 rows, which could require more from the Oracle box.
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Hidden Features of SQL Server
I've worked as a .NET developer for a while now, but predominantly against a SQL Server database for a little over 3 years now. I feel that I have a fairly decent grasp of SQL Server from a development standpoint, but I ashamed to admit that I just learned today about "WITH TIES" from this answer - Top 5 with most friends.
It is humbling to see questions and answers like this on SO because it helps me realize that I really don't know as much as I think I do and helps re-energize my will to learn more, so I figured what better way than to ask the masses of experts for input on other handy commands/features.
What is the most useful feature/command that the average developer is probably unaware of?
BTW - if you are like I was and don't know what "WITH TIES" is for, here is a good explanation. You'll see quickly why I was ashamed I was unaware of it. I could see where it could be useful though. - http://harriyott.com/2007/06/with-ties-sql-server-tip.aspx
I realize that this is a subjective question so please allow for at least a few answers before you close it. :) I'll try to edit my question to keep up a list with your response. Thanks
[EDIT] - Here is a summary of the responses Please scroll down for more information. Thanks again guys/gals.
MERGE - A single command to INSERT / UPDATE / DELETE into a table from a row source.
FILESTREAM feature of SQL Server 2008 allows storage of and efficient access to BLOB data using a combination of SQL Server 2008 and the NTFS file system
CAST - get a date without a time portion
Group By - I gotta say you should definitely know this already
SQL Server Management Studio
Transactions
The sharing of local scope temp tables between nested procedure calls
INSERT INTO
MSDN
JOINS
PIVOT and UNPIVOT
WITH(FORCESEEK) - forces the query optimizer to use only an index seek operation as the access path to the data in the table.
FOR XML
COALESCE
How to shrink the database and log files
Information_Schema
SET IMPLICIT_TRANSACTIONS in Management Studio 2005
Derived tables and common table expressions (CTEs)
OUTPUT clause - allows access to the "virtual" tables called inserted and deleted (like in triggers)
CTRL + 0 to insert null
Spacial Data in SQL Server 2008
FileStream in SQL Server 2008: FILESTREAM feature of SQL Server 2008 allows storage of and efficient access to BLOB data using a combination of SQL Server 2008 and the NTFS file system.
Creating a Table for Storing FILESTREAM Data
Once the database has a FILESTREAM filegroup, tables can be created that contain FILESTREAM columns. As mentioned earlier, a FILESTREAM column is defined as a varbinary (max) column that has the FILESTREAM attribute. The following code creates a table with a single FILESTREAM column
USE Production;
GO
CREATE TABLE DocumentStore (
DocumentID INT IDENTITY PRIMARY KEY,
Document VARBINARY (MAX) FILESTREAM NULL,
DocGUID UNIQUEIDENTIFIER NOT NULL ROWGUIDCOL
UNIQUE DEFAULT NEWID ())
FILESTREAM_ON FileStreamGroup1;
GO
In SQL Server 2008 (and in Oracle 10g): MERGE.
A single command to INSERT / UPDATE / DELETE into a table from a row source.
To generate a list of numbers from 1 to 31 (say, for a calendary):
WITH cal AS
(
SELECT 1 AS day
UNION ALL
SELECT day + 1
FROM cal
WHERE day <= 30
)
A single-column index with DESC clause in a clustered table can be used for sorting on column DESC, cluster_key ASC:
CREATE INDEX ix_column_desc ON mytable (column DESC)
SELECT TOP 10 *
FROM mytable
ORDER BY
column DESC, pk
-- Uses the index
SELECT TOP 10 *
FROM mytable
ORDER BY
column, pk
-- Doesn't use the index
CROSS APPLY and OUTER APPLY: enables to join rowsources which depend on the values of the tables being joined:
SELECT *
FROM mytable
CROSS APPLY
my_tvf(mytable.column1) tvf
SELECT *
FROM mytable
CROSS APPLY
(
SELECT TOP 5 *
FROM othertable
WHERE othertable.column2 = mytable.column1
) q
EXCEPT and INTERSECT operators: allow selecting conditions that include NULLs
DECLARE #var1 INT
DECLARE #var2 INT
DECLARE #var3 INT
SET #var1 = 1
SET #var2 = NULL
SET #var2 = NULL
SELECT col1, col2, col3
FROM mytable
INTERSECT
SELECT #val1, #val2, #val3
-- selects rows with `col1 = 1`, `col2 IS NULL` and `col3 IS NULL`
SELECT col1, col2, col3
FROM mytable
EXCEPT
SELECT #val1, #val2, #val3
-- selects all other rows
WITH ROLLUP clause: selects a grand total for all grouped rows
SELECT month, SUM(sale)
FROM mytable
GROUP BY
month WITH ROLLUP
Month SUM(sale)
--- ---
Jan 10,000
Feb 20,000
Mar 30,000
NULL 60,000 -- a total due to `WITH ROLLUP`
It's amazing how many people work unprotected with SQL Server as they don't know about transactions!
BEGIN TRAN
...
COMMIT / ROLLBACK
After creating a #TempTable in a procedure, it is available in all stored procedures that are then called from from the original procedure. It is a nice way to share set data between procedures. see: http://www.sommarskog.se/share_data.html
COALESCE() , it accepts fields and a value to use incase the fields are null.
For example if you have a table with city, State, Zipcode you can use COALESCE() to return the addresses as single strings, IE:
City | State | Zipcode
Houston | Texas | 77058
Beaumont | Texas | NULL
NULL | Ohio | NULL
if you were to run this query against the table:
select city + ‘ ‘ + COALESCE(State,’’)+ ‘ ‘+COALESCE(Zipcode, ‘’)
Would return:
Houston Texas 77058
Beaumont Texas
Ohio
You can also use it to pivot data, IE:
DECLARE #addresses VARCHAR(MAX)
SELECT #addresses = select city + ‘ ‘ + COALESCE(State,’’)+ ‘ ‘
+COALESCE(Zipcode, ‘’) + ‘,’ FROM tb_addresses
SELECT #addresses
Would return:
Houston Texas 77058, Beaumont Texas, Ohio
A lot of SQL Server developers still don't seem to know about the OUTPUT clause (SQL Server 2005 and newer) on the DELETE, INSERT and UPDATE statement.
It can be extremely useful to know which rows have been INSERTed, UPDATEd, or DELETEd, and the OUTPUT clause allows to do this very easily - it allows access to the "virtual" tables called inserted and deleted (like in triggers):
DELETE FROM (table)
OUTPUT deleted.ID, deleted.Description
WHERE (condition)
If you're inserting values into a table which has an INT IDENTITY primary key field, with the OUTPUT clause, you can get the inserted new ID right away:
INSERT INTO MyTable(Field1, Field2)
OUTPUT inserted.ID
VALUES (Value1, Value2)
And if you're updating, it can be extremely useful to know what changed - in this case, inserted represents the new values (after the UPDATE), while deleted refers to the old values before the UPDATE:
UPDATE (table)
SET field1 = value1, field2 = value2
OUTPUT inserted.ID, deleted.field1, inserted.field1
WHERE (condition)
If a lot of info will be returned, the output of OUTPUT can also be redirected to a temporary table or a table variable (OUTPUT INTO #myInfoTable).
Extremely useful - and very little known!
Marc
There are a handful of ways to get a date without a time portion; here's one that is quite performant:
SELECT CAST(FLOOR(CAST(getdate() AS FLOAT))AS DATETIME)
Indeed for SQL Server 2008:
SELECT CAST(getdate() AS DATE) AS TodaysDate
The "Information_Schema" gives me a lot of views that I can use to gather information about the SQL objects tables, procedures, views, etc.
If you are using Management Studio 2005 you can have it automatically execute your query as a transaction. In a new query window go to Query->Query Options. Then click on the ANSI "tab" (on the left). Check SET IMPLICIT_TRANSACTIONS. Click OK. Now if you run any query in this current query window it will run as a transaction and you must manually ROLLBACK or COMMIT it before continuing. Additionally, this only works for the current query window; pre-existing/new query windows will need to have the option set.
I've personally found it useful. However, it's not for the faint of heart. You must remember to ROLLBACK or COMMIT your query. It will NOT tell you that you have a pending transaction if you switch to a different query window (or even a new one). However, it will tell you if you try to close the query window.
PIVOT and UNPIVOT
FOR XML
BACKUP LOG <DB_NAME> WITH TRUNCATE_ONLY
DBCC_SHRINKDATABASE(<DB_LOG_NAME>, <DESIRED_SIZE>)
When I started to manage very large databases on MS SQL Server and the log file had over 300 GB this statements saved my life. In most cases the shrink database will have no effect.
Before running them be sure to make full backup of LOG, and after running them to do a full backup of DB (restore sequence is no longer valid).
Most SQL Server developers should know about and use derived tables and common table expressions (CTEs).
The documentation.
Sad to say, but I have come to the conclusion that the most hidden feature that developers are unaware of is the documentation on MSDN. Take for instance a Transact-SQL verb like RESTORE. The BOL will cover not only the syntax and arguments of RESTORE. But this is only the tip of the iceberg when it comes to documentation. The BOL covers:
the in depth fundamentals of recovery: Understanding How Restore and Recovery of Backups Work in SQL Server.
end-to-end scenarios on how to deploy a recovery strategy: Implementing Restore Scenarios for SQL Server Databases.
the issues around system databases: Considerations for Backing Up and Restoring System Databases.
optimizing the recovery procedures: Optimizing Backup and Restore Performance in SQL Server.
understanding how to to a restore. Backing Up and Restoring How-to Topics (Transact-SQL).
more corner cases and uncommon scenarios, there are examples like Example: Piecemeal Restore of Only Some Filegroups (Full Recovery Model).
The list goes on and on, and this is just one single topic (backup and restore). Every feature of SQL Server gets similar coverage. Reckon not everything will get the detail backup and recovery gets, but everything is documented and there are How To topics for every feature.
The amount of information available is just ludicrous. Yet the documentation is one of the most underused resources, hence my vote for it being a hidden feature.
How about materialised views? Add a clustered index to a view and you effectively create a table containing duplicate data that is automatically updated. Slows down inserts and updates because you are doing the operation twice but you make selecting a specific subset faster. And apparently the database optimiser uses it without you having to call it explicitly.
Is a view faster than a simple query?
It sounds silly to say but I've looked a lot of queries where I just asked myself does the person just not know what GROUP BY is? I'm not sure if most developers are unaware of it but it comes up enough that I wonder sometimes.
use ctrl-0 to insert a null value in a cell
WITH (FORCESEEK) which forces the query optimizer to use only an index seek operation as the access path to the data in the table.
Spacial Data in SQL Server 2008 i.e. storing Lat/Long data in a geography datatype and being able to calculate/query using the functions that go along with it.
It supports both Planar and Geodetic data.
Why am I tempted to say JOINS?
Derived tables are one of my favorites. They perform so much better than correlated subqueries but may people continue to use correlated subqueries instead.
Example of a derived table:
select f.FailureFieldName, f.RejectedValue, f.RejectionDate,
ft.FailureDescription, f.DataTableLocation, f.RecordIdentifierFieldName,
f.RecordIdentifier , fs.StatusDescription
from dataFailures f
join(select max (dataFlowinstanceid) as dataFlowinstanceid
from dataFailures
where dataflowid = 13)a
on f.dataFlowinstanceid = a.dataFlowinstanceid
join FailureType ft on f.FailureTypeID = ft.FailureTypeID
join FailureStatus fs on f.FailureStatusID = fs.FailureStatusID
When I first started working as programmer, I started with using SQL Server 2000. I had been taught DB theory on Oracle and MySQL so I didn't know much about SQL Server 2000.
But, as it turned out nor did the development staff I joined because they didn't know that you could convert datetime (and related) data types to formatted strings with built in functions. They were using a very inefficient custom function they had developed. I was more than happy to show them the errors of their ways... (I'm not with that company anymore... :-D)
With that annotate:
So I wanted to add this to the list:
select Convert(varchar, getdate(), 101) -- 08/06/2009
select Convert(varchar, getdate(), 110) -- 08-06-2009
These are the two I use most often. There are a bunch more: CAST and CONVERT on MSDN