i have 3 tables in my site.
Users
Threads
Comments
I connected the comments primary key to Threads comments field. I want to use insert into command while feeding comments to specific threads.
How do i write the command?!?
is it like this:
string myCommand="INSERT INTO [Threads].[Comments] VALUES(....";
Will the messages be inserted into a specific thread?
What if i want to insert data to both simultaneously.. e.g. a headline to a thread and a date to the comment...can i combine two commands into one?
You have set up your foreign key back to front, if you have a foreign key in the threads table that links to the primary key of the comments table then one comment can relate to many threads but a thread can only have one comment.
You have to create two separate INSERT statements. You can wrap them in a transaction to ensure that neither are committed unless they are both successful.
You still need two INSERT statements, but it sounds like you want to get the IDENTITY from the first insert and use it in the second, in which case, you might want to look into OUTPUT or OUTPUT INTO: http://msdn.microsoft.com/en-us/library/ms177564.aspx
(my answer to the same question previously asked: SQL Server: Is it possible to insert into two tables at the same time?)
I'd create a stored procedure and put both insert's into one transaction within the SP. You can use ##SCOPE_IDENTITY to get the ID from the insert into threads and use that in your insert into the comments table:
INSERT INTO [Threads] (...
INSERT INTO [Comments]
SELECT
##SCOPE_IDENTITY,
OtherValues ...
You could use a transaction as previously stated to make it more robust. Call your SP from your C# code using a SQL command.
Use two commands to insert into Threads and Comments. First insert into Threads and grab the id:
string myCommand = "INSERT INTO [Threads] (...";
// execute
string myCommand = "SELECT SCOPE_IDENTITY()";
// execute - put in thread ID
Then insert into comments using the thread ID
string myCommand = "INSERT INTO [Comments] (" + ThreadID + "...";
There is no real value or point in somehow accomplishing this in a single INSERT Command.
Edit Changed ##IDENTITY to SCOPE_IDENTITY() per comment suggestions. Thanks!
Related
I have some stored procedures in which multiple queries are being executed. To get last identity of insert I am using IDENT_CURRENT which is causuing problem.
My question is can I have lock statements like C# in T-SQL so that it can be thread safe?
EDIT: Code I am using
INSERT INTO activities
(creator
,title
,description)
VALUES
(#Creator
,#Tile
,#Description)
SET #ActivityId = IDENT_CURRENT('dbo.activities');
INSERT INTO [dbo].activity_cfs
([activity_id],
[cf_id],
[cf_field_name],
[field_key],
[value])
SELECT
#ActivityId,
cf_id,
cf_field_name,
field_key,
value
FROM #ActivityCustomFields
#ActivityCustomFields is my temp table.
It is quite likely that you should use SCOPE_IDENTITY instead of IDENT_CURRENT. There are many explanations how they differ, for example: What is the difference between Scope_Identity(), Identity(), ##Identity, and Ident_Current?
But, if you really need to guarantee that certain part of the code is not being run by several threads at the same time, you can use sp_getapplock.
Based on the code that you added to the question I'm now pretty sure that you should simply use SCOPE_IDENTITY, like this:
INSERT INTO activities
(creator
,title
,description)
VALUES
(#Creator
,#Tile
,#Description);
SET #ActivityId = SCOPE_IDENTITY();
INSERT INTO [dbo].activity_cfs
([activity_id],
[cf_id],
[cf_field_name],
[field_key],
[value])
SELECT
#ActivityId,
cf_id,
cf_field_name,
field_key,
value
FROM #ActivityCustomFields;
The SCOPE_IDENTITY function returns the last identity created in the same session and the same scope.
The IDENT_CURRENT returns the last identity created for a specific table or view in any session. So, if you have several threads that run this procedure simultaneously IDENT_CURRENT will see identities generated in other threads, which you don't want.
SCOPE_IDENTITY would be the way to go in my understanding. Please follow following link that in SQL Server when using SCOPE_IDENTITY will always be threadsafe:
http://www.vbforums.com/showthread.php?727047-RESOLVED-Is-MSSQL-s-SCOPE_IDENTITY()-thread-safe
I have created two threads in C# and I am calling two separate functions in parallel. Both functions read the last ID from XYZ table and insert new record with value ID+1. Here ID column is the primary key. When I execute the both functions I am getting primary key violation error. Both function having the below query:
insert into XYZ values((SELECT max(ID)+1 from XYZ),'Name')
Seems like both functions are reading the value at a time and trying to insert with the same value.
How can I solve this problem.. ?
Let the database handle selecting the ID for you. It's obvious from your code above that what you really want is an auto-incrementing integer ID column, which the database can definitely handle doing for you. So set up your table properly and instead of your current insert statement, do this:
insert into XYZ values('Name')
If your database table is already set up I believe you can issue a statement similar to:
alter table your_table modify column you_table_id int(size) auto_increment
Finally, if none of these solutions are adequate for whatever reason (including, as you indicated in the comments section, inability to edit the table schema) then you can do as one of the other users suggested in the comments and create a synchronized method to find the next ID. You would basically just create a static method that returns an int, issue your select id statement in that static method, and use the returned result to insert your next record into the table. Since this method would not guarantee a successful insert (due to external applications ability to also insert into the same table) you would also have to catch Exceptions and retry on failure).
Set ID column to be "Identity" column. Then, you can execute your queries as:
insert into XYZ values('Name')
I think that you can't use ALTER TABLE to change column to be Identity after column is created. Use Managament Studio to set this column to be Identity. If your table has many rows, this can be a long running process, because it will actually copy your data to a new table (will perform table re-creation).
Most likely that option is disabled in your Managament Studio. In order to enable it open Tools->Options->Designers and uncheck option "Prevent saving changes that require table re-creation"...depending on your table size, you will probably have to set timeout, too. Your table will be locked during that time.
A solution for such problems is to have generate the ID using some kind of a sequence.
For example, in SQL Server you can create a sequence using the command below:
CREATE SEQUENCE Test.CountBy1
START WITH 1
INCREMENT BY 1 ;
GO
Then in C#, you can retrieve the next value out of Test and assign it to the ID before inserting it.
It sounds like you want a higher transaction isolation level or more restrictive locking.
I don't use these features too often, so hopefully somebody will suggest an edit if I'm wrong, but you want one of these:
-- specify the strictest isolation level
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
insert into XYZ values((SELECT max(ID)+1 from XYZ),'Name')
or
-- make locks exclusive so other transactions cannot access the same rows
insert into XYZ values((SELECT max(ID)+1 from XYZ WITH (XLOCK)),'Name')
How can I insert values into two tables at once?
if it not successful, both table should rollback.
I am using SQL server and the query passe throw C# code.
You could either run the two queries as one statement
insert into table1 (...) values (...); insert into table2 (...) values (...)
or write a trigger to do the second INSERT.
I would typically write a stored procedure to take in all of the values you want to write out, then call a series of INSERT INTO statements wrapped in a transaction.
If you provide more information, such as table structure and sample data, we can help you further.
get ans here of ur question
SQL Server: Is it possible to insert into two tables at the same time?
How can I INSERT data into two tables simultaneously in SQL Server?
I use asp.net 4 and DataSets for accessing the database. There are two tables with one-to-one relationship in the database. It means that both tables have the same column as a primary key (say Id), and one of tables has #identity on this column set.
So in general if we want to insert, we insert first into the first table, than insert into the second table with id.table2 = id of the corresponding record in table1.
I can imagine how to achieve this using stored procedure (we would insert into the first table and have id as an out parameter and then insert into the second table using this id, btw all inside one transaction).
But is there a way to do it without using a stored procedure? May be DataSets \ DataAdapters have such functionality built in?
Would appreciate any help.
Today it is so quiet here... Ok if anybody is also looking for such a solution, I've found a way to do it.
So our main problem is to get the id of the newly created record in the first table. If we're able to do that, after that we simply supply it to the next method which creates a corresponding record in the second table.
I used a DataSet Designer in order to enjoy the code autogeneration feature of the VS. Let's call the first table TripSets. In DataSet Designer right click on the TripSetsTableAdapter, then Properties. Expand InsertCommand properties group. Here we need to do two things.
First we add a new parameter into the collection of parameters using the Parameters Collection Editor. Set ParameterName = #TripId, DbType = Int32 (or whatever you need), Direction = Output.
Second we modify the CommandText (using Query Builder for convenience). Add to the end of the command another one after a semicolon like that:
(...);
SELECT #TripId = SCOPE_IDENTITY()
So you will get something like this statement:
INSERT INTO TripSets
(Date, UserId)
VALUES
(#Date,#UserId);
SELECT #TripId = SCOPE_IDENTITY()
Perhaps you will get a parser error warning, but you can just ignore it. Having this configured now we are able to use in our Business logic code as follows:
int tripId;
int result = tripSetsTableAdapter.Insert(tripDate, userId, out tripId);
// Here comes the insert method into the second table
tripSetTripSearchTableAdapter.Insert(tripId, amountPersons);
Probably you will want to synchronize this operations somehow (e.g. using TransactionScope) but it is completely up to you.
I have a table, schema is very simple, an ID column as unique primary key (uniqueidentifier type) and some other nvarchar columns. My current goal is, for 5000 inputs, I need to calculate what ones are already contained in the table and what are not. Tht inputs are string and I have a C# function which converts string into uniqueidentifier (GUID). My logic is, if there is an existing ID, then I treat the string as already contained in the table.
My question is, if I need to find out what ones from the 5000 input strings are already contained in DB, and what are not, what is the most efficient way?
BTW: My current implementation is, convert string to GUID using C# code, then invoke/implement a store procedure which query whether an ID exists in database and returns back to C# code.
My working environment: VSTS 2008 + SQL Server 2008 + C# 3.5.
My first instinct would be to pump your 5000 inputs into a single-column temporary table X, possibly index it, and then use:
SELECT X.thecol
FROM X
JOIN ExistingTable USING (thecol)
to get the ones that are present, and (if both sets are needed)
SELECT X.thecol
FROM X
LEFT JOIN ExistingTable USING (thecol)
WHERE ExistingTable.thecol IS NULL
to get the ones that are absent. Worth benchmarking, at least.
Edit: as requested, here are some good docs & tutorials on temp tables in SQL Server. Bill Graziano has a simple intro covering temp tables, table variables, and global temp tables. Randy Dyess and SQL Master discuss performance issue for and against them (but remember that if you're getting performance problems you do want to benchmark alternatives, not just go on theoretical considerations!-).
MSDN has articles on tempdb (where temp tables are kept) and optimizing its performance.
Step 1. Make sure you have a problem to solve. Five thousand inserts isn't a lot to insert one at a time in a lot of contexts.
Are you certain that the simplest way possible isn't sufficient? What performance issues have you measured so far?
What do you need to do with those entries that do or don't exist in your table??
Depending on what you need, maybe the new MERGE statement in SQL Server 2008 could fit your bill - update what's already there, insert new stuff, all wrapped neatly into a single SQL statement. Check it out!
http://blogs.conchango.com/davidportas/archive/2007/11/14/SQL-Server-2008-MERGE.aspx
http://www.sql-server-performance.com/articles/dba/SQL_Server_2008_MERGE_Statement_p1.aspx
http://blogs.msdn.com/brunoterkaly/archive/2008/11/12/sql-server-2008-merge-capability.aspx
Your statement would look something like this:
MERGE INTO
(your target table) AS t
USING
(your source table, e.g. a temporary table) AS s
ON t.ID = s.ID
WHEN NOT MATCHED THEN -- new rows does not exist in base table
....(do whatever you need to do)
WHEN MATCHED THEN -- row exists in base table
... (do whatever else you need to do)
;
To make this really fast, I would load the "new" records from e.g. a TXT or CSV file into a temporary table in SQL server using BULK INSERT:
BULK INSERT YourTemporaryTable
FROM 'c:\temp\yourimportfile.csv'
WITH
(
FIELDTERMINATOR =',',
ROWTERMINATOR =' |\n'
)
BULK INSERT combined with MERGE should give you the best performance you can get on this planet :-)
Marc
PS: here's a note from TechNet on MERGE performance and why it's faster than individual statements:
In SQL Server 2008, you can perform multiple data manipulation language (DML) operations in a single statement by using the MERGE statement. For example, you may need to synchronize two tables by inserting, updating, or deleting rows in one table based on differences found in the other table. Typically, this is done by executing a stored procedure or batch that contains individual INSERT, UPDATE, and DELETE statements. However, this means that the data in both the source and target tables are evaluated and processed multiple times; at least once for each statement.
By using the MERGE statement, you can replace the individual DML statements with a single statement. This can improve query performance because the operations are performed within a single statement, therefore, minimizing the number of times the data in the source and target tables are processed. However, performance gains depend on having correct indexes, joins, and other considerations in place. This topic provides best practice recommendations to help you achieve optimal performance when using the MERGE statement.
Try to ensure you end up running only one query - i.e. if your solution consists of running 5000 queries against the database, that'll probably be the biggest consumer of resources for the operation.
If you can insert the 5000 IDs into a temporary table, you could then write a single query to find the ones that don't exist in the database.
If you want simplicity, since 5000 records is not very many, then from C# just use a loop to generate an insert statement for each of the strings you want to add to the table. Wrap the insert in a TRY CATCH block. Send em all up to the server in one shot like this:
BEGIN TRY
INSERT INTO table (theCol, field2, field3)
SELECT theGuid, value2, value3
END TRY BEGIN CATCH END CATCH
BEGIN TRY
INSERT INTO table (theCol, field2, field3)
SELECT theGuid, value2, value3
END TRY BEGIN CATCH END CATCH
BEGIN TRY
INSERT INTO table (theCol, field2, field3)
SELECT theGuid, value2, value3
END TRY BEGIN CATCH END CATCH
if you have a unique index or primary key defined on your string GUID, then the duplicate inserts will fail. Checking ahead of time to see if the record does not exist just duplicates work that SQL is going to do anyway.
If performance is really important, then consider downloading the 5000 GUIDS to your local station and doing all the analysis localy. Reading 5000 GUIDS should take much less than 1 second. This is simpler than bulk importing to a temp table (which is the only way you will get performance from a temp table) and doing an update using a join to the temp table.
Since you are using Sql server 2008, you could use Table-valued parameters. It's a way to provide a table as a parameter to a stored procedure.
Using ADO.NET you could easily pre-populate a DataTable and pass it as a SqlParameter.
Steps you need to perform:
Create a custom Sql Type
CREATE TYPE MyType AS TABLE
(
UniqueId INT NOT NULL,
Column NVARCHAR(255) NOT NULL
)
Create a stored procedure which accepts the Type
CREATE PROCEDURE spInsertMyType
#Data MyType READONLY
AS
xxxx
Call using C#
SqlCommand insertCommand = new SqlCommand(
"spInsertMyType", connection);
insertCommand.CommandType = CommandType.StoredProcedure;
SqlParameter tvpParam =
insertCommand.Parameters.AddWithValue(
"#Data", dataReader);
tvpParam.SqlDbType = SqlDbType.Structured;
Links: Table-valued Parameters in Sql 2008
Definitely do not do it one-by-one.
My preferred solution is to create a stored procedure with one parameter that can take and XML in the following format:
<ROOT>
<MyObject ID="60EAD98F-8A6C-4C22-AF75-000000000000">
<MyObject ID="60EAD98F-8A6C-4C22-AF75-000000000001">
....
</ROOT>
Then in the procedure with the argument of type NCHAR(MAX) you convert it to XML, after what you use it as a table with single column (lets call it #FilterTable). The store procedure looks like:
CREATE PROCEDURE dbo.sp_MultipleParams(#FilterXML NVARCHAR(MAX))
AS BEGIN
SET NOCOUNT ON
DECLARE #x XML
SELECT #x = CONVERT(XML, #FilterXML)
-- temporary table (must have it, because cannot join on XML statement)
DECLARE #FilterTable TABLE (
"ID" UNIQUEIDENTIFIER
)
-- insert into temporary table
-- #important: XML iS CaSe-SenSiTiv
INSERT #FilterTable
SELECT x.value('#ID', 'UNIQUEIDENTIFIER')
FROM #x.nodes('/ROOT/MyObject') AS R(x)
SELECT o.ID,
SIGN(SUM(CASE WHEN t.ID IS NULL THEN 0 ELSE 1 END)) AS FoundInDB
FROM #FilterTable o
LEFT JOIN dbo.MyTable t
ON o.ID = t.ID
GROUP BY o.ID
END
GO
You run it as:
EXEC sp_MultipleParams '<ROOT><MyObject ID="60EAD98F-8A6C-4C22-AF75-000000000000"/><MyObject ID="60EAD98F-8A6C-4C22-AF75-000000000002"/></ROOT>'
And your results look like:
ID FoundInDB
------------------------------------ -----------
60EAD98F-8A6C-4C22-AF75-000000000000 1
60EAD98F-8A6C-4C22-AF75-000000000002 0