I have a stored procedure in BQ where the results i want to be stored inside a temp table for further analysis.
How can we do it inside BQ?
Temporary tables are session based, i.e. they only live within a Begin and an End block. Temp tables can be created inside a Stored procedure but are not accessible outside it.
You can create a temp table using following syntax - Reference
CREATE TEMP TABLE <ANALYTICS_TABLE> ...
You can use this Temp Table throughout the procedure to perform Data transformations, cleansing etc.
Temp tables are recommended when you have multiple transformations which refer to a common Transformation, which can be saved as a Temp table for intermediate use.
Consider Transformation 1 & Transformation 2 to be heavy operations. Transformation 3 & 4 both utilise common Transformation 2, Hence to avoid re-computations of Transformation 2, it's better to save it as a temp table to be referred multiple times.
But in order to save the results, you must save them to a Permanent Table in order to persist it. Permanent table then can be queries in other procedures and you can Create Views on top of them.
Related
Image #1: I am creating a stored procedure for inserting records into #t1.
In the same session I am executing the Localtemp1 stored procedure for any number of times, and it works fine:
Image #2: again executing the stored procedure in another session & works fine as well:
Image #3: now creating stored procedure for inserting records into ##tt. For the first execution of globaltemp1 stored procedure, it works well:
Image #4: but when I executed it a second time, it is showing errors (does not exist in DB):
Image #5: then I closed the session where globaltemp stored procedure was created, and in a new session, I executed the stored procedure, and it works well for the first time:
Image #6: but when I execute it a second time, again it is showing errors (does not exist in DB):
What I know is scope of local temp & global temp, but in stored procedures, they were completely different
Can someone tell me
Execution of localtemp1 stored procedure for many times gives output but while executing globaltemp1 sp for the first time gives output and second time results in an error
As far as I know, after execution of stored procedure temptable gets dropped. Then why localtemp1 stored procedure is getting executed across all sessions and many number of times?
Why globaltemp1 stored procedure is executing once and for second time showing an error?
Final one, Globaltemp stored procedure shows output in another session for the first time only when created session was closed
I mean
56 ----> globaltemp sp was created
57 ----> to get o/p i need to close 56
58 ----> to get o?p i need to close 57 ( WHY ??? )
I am a beginner at SQL and please, someone make me understand because if I don't find logic & correct reason I could not dive into another topic.
The concept of temp table is to hold records temporarily. It's some kind of an array where you can store multiple records using the same variable.
When you create a Temp Table, actually it is being created in the tempdb of the corresponding server. Even if you are naming it as just #temp, the name on which it was created on the tempdb will be having some additional parameters like your database name from which the table was created and your session id etc.
I just created the following temp table in my master database
and this is how it was named in the tempdb
still, in my database, I can access it using the name #temp. But The limitation of such temp table is that they are local and can be accessed only from that session, So if I try to access this #temp from any other Query Window (Session) even on the same database, I won't be able to access it. That's where we use Global temp tables. So If I add one more # to the table name then it becomes global temp table which can be accessed across the sessions. It is still created on the Tempdb but like this
Whenever you close the query window/session both Local and Global temp tables are automatically dropped.
So in the case of stored procedures, the starting and ending time of the sp is treated as one session. So once the sp execution is completed all the temp tables created inside that sp is dropped. So you can not use one temp table that was created by one SP in another one.
Hope this helps
Local temporary tables are visible only in the current session, and global temporary tables are visible to all sessions. Global temporary tables are automatically dropped when the session that created the table ends and all other tasks have stopped referencing them. The association between a task and a table is maintained only for the life of a single Transact-SQL statement. This means that a global temporary table is dropped at the completion of the last Transact-SQL statement that was actively referencing the table when the creating session ended.
If you have absolutely have to have a global temp table available your best solution would be to create a permanent table and then drop the table at the end of the stored procedure. You can check for it's existence before creating it:
IF OBJECT_ID('dbo.yourtablenamehere', 'U') IS NOT NULL
DROP TABLE dbo.yourtablenamehere;
The differences between a temp table and a permanent table are really not that much different, mostly that the temp table drops automatically. If you are using this in an application that is calling this procedure, it might be best to have the application load the temp table into array and do the comparisons for you since it can maintain the array while executing and re-executing stored procs.
There is a good reason to write to a temp table instead of creating a table then dropping it... access rights. If you are creating tables to be used by people who are only granted read only privileges, they will not be able to create the table.
I know basic sql commands, and this is my first time working with stored procedures. In the stored procedure I am looking at, there are several temporary tables.
The procedure, is triggerred every morning, which then pulls a specific ID and then loops through each ID to grab certain parameters.
My question is: are temporary tables used in stored procedures so that when the procedure goes off the variables will be instantly passed into the parameters and loop, and then the temporary tables will be cleared, thus restarting the process for the next loop?
Temporary tables are used because as soon as the session that created them (or stored procedure) is closed the temporary table is gone. A Temp table with a single # in front of the name (also called a local temp table) is only visible in the session it was created in so a temp table with the same name can be created in multiple sessions without bumping into each other (SQL Server adds characters to the name to make it unique). If a temp table with two ## in front of it is created (a global temp table) then it is unique within SQL Server so other sessions can see it. Temp tables are the equivalent of a scratch pad. When SQL Server is restarted all temp tables and their values are gone. Temp tables can have indexes created against them and SQL Server can use statistics on Temp tables to create efficient query plans.
For stored procedures (SPs), they are the least restricted and most capable objects, for example:
Their usual alternatives, views and functions, are not allowed to utilize many things, like DML statements, temp. tables, transactions, etc.
SPs can avoid returning result sets. They also can return more than one result set.
For temp. tables:
Yes, once the SP is done, the table disappears along with its
contents (at least for single-# tables).
They have advantages &
disadvantages compared to their alternatives (actual tables, table
varaibles, various non-table solutions).
Stored Procedures, in my opinion, don't forcibly need Temporary tables. It's up to the SP's scope to decide if using a TempTable is the best approach.
For example, let's suppose that we want to retrieve a List of elements that come out from joining a few tables, then it's the best to have a TempTable to put the joined fields. On the other hand, if we're using a Stored Procedure to retrieve a single or field, I don't see the need for a Temp table.
Temp tables are only available during the usage of the Stored Procedure, once it's finished, the table goes out of scope.
I can think of two main benefits:
Avoiding concurrency problems, if you have many processes creating/dropping tables you can get in trouble as one process tries to create an already existing table.
Performance, I imagine that creating temporary tables (with #) is more performant than regular tables.
Is there any other reason, and is any of my reasons false?
You can't compare temporary and persistent tables:
Persistent tables keep your data and can be used by any process.
Temporary ones are throw away and #ones are visible only to that connection
You'd use a temp table to spool results for further processing and such.
There is little difference in performance (either way) between the two types of table.
You shouldn't be dropping and creating tables all the time... any app that relies on this is doing something wrong, not least way too many SQL calls.
(1)Temp Tables are created in the SQL Server TEMPDB database and therefore require more IO resources and locking. Table Variables and Derived Tables are created in memory.
(2)Temp Tables will generally perform better for large amounts of data that can be worked on using parallelism whereas Table Variables are best used for small amounts of data (I use a rule of thumb of 100 or less rows) where parallelism would not provide a significant performance improvement.
(3)You cannot use a stored procedure to insert data into a Table Variable or Derived Table. For example, the following will work: INSERT INTO #MyTempTable EXEC dbo.GetPolicies_sp whereas the following will generate an error: INSERT INTO #MyTableVariable EXEC dbo.GetPolicies_sp.
(4)Derived Tables can only be created from a SELECT statement but can be used within an Insert, Update, or Delete statement.
(5) In order of scope endurance, Temp Tables extend the furthest in scope, followed by Table Variables, and finally Derived Tables.
1)
A table variable's lifespan is only for the duration of the transaction that it runs in. If we execute the DECLARE statement first, then attempt to insert records into the #temp table variable we receive the error because the table variable has passed out of existence. The results are the same if we declare and insert records into #temp in one transaction and then attempt to query the table. If you notice, we need to execute a DROP TABLE statement against #temp. This is because the table persists until the session ends or until the table is dropped.
2)
table variables have certain clear limitations.
-Table variables can not have Non-Clustered Indexes
-You can not create constraints in table variables
-You can not create default values on table variable columns
-Statistics can not be created against table variables
-Similarities with temporary tables include:
Similarities with temporary tables include:
-Instantiated in tempdb
-Clustered indexes can be created on table variables and temporary tables
-Both are logged in the transaction log
-Just as with temp and regular tables, users can perform all Data Modification Language -(DML) queries against a table variable: SELECT, INSERT, UPDATE, and DELETE.
here's the situation:
I have an SSRS report that uses an SP as a Dataset. The SP creates a Temp Table, inserts a bunch of data into it, and select's it back out for SSRS to report. Pretty straight forward.
Question:
If multiple users run the report with different parameters selected, will the temp table created by the SP collide in the tempdb and potentially not return the data set expected?
Most likely not. If the temp table is defined as #temp or #temp, then you're safe, as those kind of temp tables can only be accessed by the creating connection, and will only last for the duration of the execution of the stored procedure. If, however, you're using ##temp tables (two "pound" signs), while those tables also only last for as long as the creating stored procedure runs, they are exposed to and accessible by all connections to that SQL instance.
Odds are good that you're not using ##tables, so you are probably safe.
A temp table with a single # is a local temporary table and its scope is limited to the session that created it, so collisions should not be a problem.
I've read around the subject of temporary tables and scope and all the answers i've seen don't seem to talk about one of my concerns.
I understand that a local temporary table's scope is only valid withing the lifetime of a stored procedure or child stored procedures. However what is the situation with regard to concurency. i.e. if i have a stored procedure that creates a temporary table which is called from two different processes but from the same user/connection string, will that temporary table be shared between the two calls to that one stored procedure or will it be a case of each call to the stored procedure creates an unique temporary table instance.
I would assume that the temporary table belongs to the scope of the call to the stored procdure but i want to be sure before i go down a path with this.
Local temporary tables (start with #) are limited to your session; other sessions, even from the same user/connection string, can't see them. The rules for the lifetime depend on whether the local temporary table was created in a stored procedure:
A local temporary table that is created in a stored procedure is dropped when the procedure ends; other stored procedures, or the calling process, can't see them.
Other local temporary tables are dropped when the session ends.
Global temporary tables (start with ##) are shared between sessions. They are dropped when:
The session that created them ends
AND no other session is referring to them
This command can be handy to see which temporary tables exist:
select TABLE_NAME from tempdb.information_schema.tables
And this is handy to drop temporary tables if you're not sure they exist:
if object_id('tempdb..#SoTest') is not null drop table #SoTest
See this MSDN article for more information.
The temporary table will be accesible to the instance of the procedure that creates it
The following script
Exec ('Select 1 as col Into #Temp Select * From #Temp')
Exec ('Select 2 as col Into #Temp Select * From #Temp')
Returns
Col
1
Col
2
Not
Col
1
2
Or an error because the table already exists.
The temporary table will also be accesible by any 'child' procedures that the initial procedure runs as well.
You might also think about using table variables. They have a very well-defined scope, and they are sometimes faster than their temporary table counterparts. The only problem with table variables is that they cannot be indexed, so some performance could be lost despite their nature. Check here for some more information on the subject.