I have a scenario where I need to execute queries on different tables using ETL tool.
I want to store all the required queries in control table.
As part of this, I want to include the column WatermarkValue as part of the value in the column Source_Query, so that I can dynamically use it for my execution. This is how my control table should look like.
Table Name: Metadata_Table
TableID
Source_Query
WatermarkValue
1
select * from dbo.cust_eventchanges where lastmodifieddate >{WatermarkValue}
2022-10-09T12:00:00
2
select * from dbo.cust_contacts where lastmodifieddate >{WatermarkValue}
2022-07-08T03:20:00
So when I run my metadata table like this
select * from Metadata_Table where TableID=1
the result should be like below.
select * from dbo.cust_eventchanges where lastmodifieddate >'2022-10-09T12:00:00'
I know we can do this by concatenating two columns. But I would like to know if this is achievable.
I couldn't able to figure out how to achieve this. Hence, I need help on this scenario
Using sp_executesql with a typed parameter definition reduces the risk of SQL Injection
Example below shows how to run one of your queries. You could simply wrap this in a cursor where each iteration executes a different query in the metadata table.
DROP TABLE IF EXISTS #MetaData_Table
GO
CREATE TABLE #MetaData_Table
(TableID INT,Source_Query NVARCHAR(MAX),WatermarkValue DATETIME)
INSERT INTO #MetaData_Table
(TableID,Source_Query,WatermarkValue)
VALUES
(1,'select * from dbo.cust_eventchanges where lastmodifieddate >#WatermarkValue','2022-10-09T12:00:00'),
(2,'select * from dbo.cust_contacts where lastmodifieddate >#WatermarkValue','2022-07-08T03:20:00')
SELECT * FROM #MetaData_Table
DECLARE #dtVariable DATETIME;
DECLARE #SQLString NVARCHAR(500);
DECLARE #ParmDefinition NVARCHAR(500);
-- You can put this in a cursor to loop through all your tables, this is hardcoded to one for simplicity.
SELECT #SQLString = Source_Query, #dtVariable = WatermarkValue FROM #MetaData_Table WHERE TableID = 1
SET #ParmDefinition = N'#WatermarkValue DATETIME'
EXECUTE sp_executesql #SQLString, #ParmDefinition,
#WatermarkValue = #dtVariable;
You can create a view and use a view in your ETL tool instead of the table.
create view vMetadataQueries
as
select TableID, Source_Query + WatermarkValue as [ExecuteQuery]
from Metadata_Table
This is not a particularly good way of doing that because it potentially leaves you open to SQL injection.
Related
It looks like #temptables created using dynamic SQL via the EXECUTE string method have a different scope and can't be referenced by "fixed" SQLs in the same stored procedure.
However, I can reference a temp table created by a dynamic SQL statement in a subsequence dynamic SQL but it seems that a stored procedure does not return a query result to a calling client unless the SQL is fixed.
A simple 2 table scenario:
I have 2 tables. Let's call them Orders and Items. Order has a Primary key of OrderId and Items has a Primary Key of ItemId. Items.OrderId is the foreign key to identify the parent Order. An Order can have 1 to n Items.
I want to be able to provide a very flexible "query builder" type interface to the user to allow the user to select what Items he want to see. The filter criteria can be based on fields from the Items table and/or from the parent Order table. If an Item meets the filter condition including and condition on the parent Order if one exists, the Item should be return in the query as well as the parent Order.
Usually, I suppose, most people would construct a join between the Item table and the parent Order tables. I would like to perform 2 separate queries instead. One to return all of the qualifying Items and the other to return all of the distinct parent Orders. The reason is two fold and you may or may not agree.
The first reason is that I need to query all of the columns in the parent Order table and if I did a single query to join the Orders table to the Items table, I would be repoeating the Order information multiple times. Since there are typically a large number of items per Order, I'd like to avoid this because it would result in much more data being transfered to a fat client. Instead, as mentioned, I would like to return the two tables individually in a dataset and use the two tables within to populate a custom Order and child Items client objects. (I don't know enough about LINQ or Entity Framework yet. I build my objects by hand). The second reason I would like to return two tables instead of one is because I already have another procedure that returns all of the Items for a given OrderId along with the parent Order and I would like to use the same 2-table approach so that I could reuse the client code to populate my custom Order and Client objects from the 2 datatables returned.
What I was hoping to do was this:
Construct a dynamic SQL string on the Client which joins the orders table to the Items table and filters appropriate on each table as specified by the custom filter created on the Winform fat-client app. The SQL build on the client would have looked something like this:
TempSQL = "
INSERT INTO #ItemsToQuery
OrderId, ItemsId
FROM
Orders, Items
WHERE
Orders.OrderID = Items.OrderId AND
/* Some unpredictable Order filters go here */
AND
/* Some unpredictable Items filters go here */
"
Then, I would call a stored procedure,
CREATE PROCEDURE GetItemsAndOrders(#tempSql as text)
Execute (#tempSQL) --to create the #ItemsToQuery table
SELECT * FROM Items WHERE Items.ItemId IN (SELECT ItemId FROM #ItemsToQuery)
SELECT * FROM Orders WHERE Orders.OrderId IN (SELECT DISTINCT OrderId FROM #ItemsToQuery)
The problem with this approach is that #ItemsToQuery table, since it was created by dynamic SQL, is inaccessible from the following 2 static SQLs and if I change the static SQLs to dynamic, no results are passed back to the fat client.
3 around come to mind but I'm look for a better one:
1) The first SQL could be performed by executing the dynamically constructed SQL from the client. The results could then be passed as a table to a modified version of the above stored procedure. I am familiar with passing table data as XML. If I did this, the stored proc could then insert the data into a temporary table using a static SQL that, because it was created by dynamic SQL, could then be queried without issue. (I could also investigate into passing the new Table type param instead of XML.) However, I would like to avoid passing up potentially large lists to a stored procedure.
2) I could perform all the queries from the client.
The first would be something like this:
SELECT Items.* FROM Orders, Items WHERE Order.OrderId = Items.OrderId AND (dynamic filter)
SELECT Orders.* FROM Orders, Items WHERE Order.OrderId = Items.OrderId AND (dynamic filter)
This still provides me with the ability to reuse my client sided object-population code because the Orders and Items continue to be returned in two different tables.
I have a feeling to, that I might have some options using a Table data type within my stored proc, but that is also new to me and I would appreciate a little bit of spoon feeding on that one.
If you even scanned this far in what I wrote, I am surprised, but if so, I woul dappreciate any of your thoughts on how to accomplish this best.
You first need to create your table first then it will be available in the dynamic SQL.
This works:
CREATE TABLE #temp3 (id INT)
EXEC ('insert #temp3 values(1)')
SELECT *
FROM #temp3
This will not work:
EXEC (
'create table #temp2 (id int)
insert #temp2 values(1)'
)
SELECT *
FROM #temp2
In other words:
Create temp table
Execute proc
Select from temp table
Here is complete example:
CREATE PROC prTest2 #var VARCHAR(100)
AS
EXEC (#var)
GO
CREATE TABLE #temp (id INT)
EXEC prTest2 'insert #temp values(1)'
SELECT *
FROM #temp
1st Method - Enclose multiple statements in the same Dynamic SQL Call:
DECLARE #DynamicQuery NVARCHAR(MAX)
SET #DynamicQuery = 'Select * into #temp from (select * from tablename) alias
select * from #temp
drop table #temp'
EXEC sp_executesql #DynamicQuery
2nd Method - Use Global Temp Table:
(Careful, you need to take extra care of global variable.)
IF OBJECT_ID('tempdb..##temp2') IS NULL
BEGIN
EXEC (
'create table ##temp2 (id int)
insert ##temp2 values(1)'
)
SELECT *
FROM ##temp2
END
Don't forget to delete ##temp2 object manually once your done with it:
IF (OBJECT_ID('tempdb..##temp2') IS NOT NULL)
BEGIN
DROP Table ##temp2
END
Note: Don't use this method 2 if you don't know the full structure on database.
I had the same issue that #Muflix mentioned. When you don't know the columns being returned, or they are being generated dynamically, what I've done is create a global table with a unique id, then delete it when I'm done with it, this looks something like what's shown below:
DECLARE #DynamicSQL NVARCHAR(MAX)
DECLARE #DynamicTable VARCHAR(255) = 'DynamicTempTable_' + CONVERT(VARCHAR(36), NEWID())
DECLARE #DynamicColumns NVARCHAR(MAX)
--Get "#DynamicColumns", example: SET #DynamicColumns = '[Column1], [Column2]'
SET #DynamicSQL = 'SELECT ' + #DynamicColumns + ' INTO [##' + #DynamicTable + ']' +
' FROM [dbo].[TableXYZ]'
EXEC sp_executesql #DynamicSQL
SET #DynamicSQL = 'IF OBJECT_ID(''tempdb..##' + #DynamicTable + ''' , ''U'') IS NOT NULL ' +
' BEGIN DROP TABLE [##' + #DynamicTable + '] END'
EXEC sp_executesql #DynamicSQL
Certainly not the best solution, but this seems to work for me.
I would strongly suggest you have a read through http://www.sommarskog.se/arrays-in-sql-2005.html
Personally I like the approach of passing a comma delimited text list, then parsing it with text to table function and joining to it. The temp table approach can work if you create it first in the connection. But it feel a bit messier.
Result sets from dynamic SQL are returned to the client. I have done this quite a lot.
You're right about issues with sharing data through temp tables and variables and things like that between the SQL and the dynamic SQL it generates.
I think in trying to get your temp table working, you have probably got some things confused, because you can definitely get data from a SP which executes dynamic SQL:
USE SandBox
GO
CREATE PROCEDURE usp_DynTest(#table_type AS VARCHAR(255))
AS
BEGIN
DECLARE #sql AS VARCHAR(MAX) = 'SELECT * FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_TYPE = ''' + #table_type + ''''
EXEC (#sql)
END
GO
EXEC usp_DynTest 'BASE TABLE'
GO
EXEC usp_DynTest 'VIEW'
GO
DROP PROCEDURE usp_DynTest
GO
Also:
USE SandBox
GO
CREATE PROCEDURE usp_DynTest(#table_type AS VARCHAR(255))
AS
BEGIN
DECLARE #sql AS VARCHAR(MAX) = 'SELECT * INTO #temp FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_TYPE = ''' + #table_type + '''; SELECT * FROM #temp;'
EXEC (#sql)
END
GO
EXEC usp_DynTest 'BASE TABLE'
GO
EXEC usp_DynTest 'VIEW'
GO
DROP PROCEDURE usp_DynTest
GO
Say, I have 100 columns in a table. I do not know in which columns a particular value could exist. So, I would like to check across all columns, if it exists in any of the 100 columns, I would like to select it.
I searched around a bit, and in most places the solution seems to be something like the following
select *
from tablename
where col1='myval'
or col2='myval'
or col3='myval'
or .. or col100='myval'
I also read a few forums where having to do this is said to be a bad case of database design, I agree, but I'm working on an already existing table in a database.
Is there a more intelligent way to do this?
One way is by reversing the In operator
select *
from yourtable
where 'Myval' in (col1,col2,col3,...)
If you don't want to manually type the columns use dynamic sql to generate the query
declare #sql varchar(max)='select *
from yourtable
where ''Myval'' in ('
select #sql+=quotename(column_name)+',' from INFORMATION_SCHEMA.COLUMNS
where TABLE_NAME='yourtable'
select #sql =left(#sql,len(#sql)-1)+')'
--print #sql
exec sp_executesql #sql
I am working on a reporting project based in SQL but I have restricted access to the DB; I can only make SELECT Queries and insert the data I retrieve into temp Tables/table variables. I cannot create/execute stored procedures or any sort of functions.
The query I am running is meant to pool together all Engineers and the different key skills that they have so that we can later on see what Skills each engineer has or which Engineers fall under a certain skill.
To this end, I am trying to create a table variable/temp table with a flexible structure, a structure based on previously obtained values in the same query.
For E.g.
1st Output:
Adam
Brad
Julio
Martinez
2nd Output (Skill separated by white space):
VOIP
TTS
DBA
Exchange
Server
Create temp table/table variable that uses 1st output as rows and 2nd output as columns or vice versa. I will then populate this new table according to different values on the main DB.
Please advise how this can be done, or provide any other solution to this problem.
Thank you
I believe you can.
First of all you need to create temp table with dynamic structure based on query. It can be done like this:
declare script template:
Set #ScriptTmpl = 'Alter table #tempTable Add [?] varchar(100);
build script that will insert columns you need based on query:
Select #TableScript = #TableScript + Replace(#ScriptTmpl, '?',
ColumnName) From ... Where ...
then execute script and then fill your new table with values from second query
UPD:
here is the full sample of temporary table dynamic creation. I used global temporary table in my sample:
declare #scriptTemplate nvarchar(MAX)
declare #script nvarchar(MAX)
declare #tableTemplate nvarchar(MAX)
SET #tableTemplate = 'create table ##tmptable (?)'
SET #scriptTemplate = '? nvarchar(500),'
SET #script = ''
Drop table ##tmptable
Select #script = #script + Replace(#scriptTemplate, '?', [Name])
From Account
Where name like 'ES_%'
SET #script = LEFT(#script, LEN(#script) - 1)
SET #script = Replace(#tableTemplate, '?', #script)
Select #script
exec(#script)
Select * from ##tmptable
Firstly, you may be able to achieve what you want through pivots, rather than temporary tables.
Secondly, if you really want to create a table with column name "Adam Brad", the solution is dynamic SQL, which you may not be able to do based on your permissions.
I need som help with a problem, our company have a vendor that deliver a database to us. inside that database, the vendor has a table with alot of t sql scripts. What i want to do is the following, i want to make a select to find the script and then execut the script and store the result in a variable or temp tabel. I can not alter the script from the vedor, so I need the result into something i can manupilate. Another problem is that i dont know how many columns ther result will have. So it has to be flexible. Like one script have 5 columns and and the next script has 8 and so on.
exsample:
DECLARE #SQL nvarchar(MAX) = ( Select distinct script_details
from scripttable where .......)
This will give me the script I want to use, then I use
EXEC(#SQL)
to execute the script.
Then my problem is, the result from this I want into a variable or a table.
I have tryed to make a temp table like this:
create table #TmpTblSP (col1 varchar(MAX),col2 varchar(MAX),col3 varchar(MAX),col4 varchar(MAX),col5 varchar(MAX),col6 varchar(MAX),col7 varchar(MAX),col8 varchar(MAX),col9 varchar(MAX),col10 varchar(MAX),col11 varchar(MAX),col12 varchar(MAX))
then
insert into #TmpTblSP
EXEC(#SQL)
This gives me the following error:
Msg 213, Level 16, State 7, Line 1
Column name or number of supplied values does not match table definition.
But if i know how many columns there are and specify that into the insert it works.
insert into #TmpTblSP(Col1,Col2,Col3)
EXEC(#SQL)
But here you se my problem, I dont know how many columns there are in every script. I could make one script for every script the vendor has, but that will be alot, it's like 3000 scripts in that table and they change them often.
You could try something like:
DECLARE #SQL nvarchar(MAX) = (
Select distinct script_details
into #temptbl
from scripttable where .......
);
EXEC(#SQL);
If you don't know how many columns yous #sql gives then the only solution is use SELECT INTO. I use it in this way:
DECLARE #QRY nvarchar(MAX) = ( Select distinct script_details
from scripttable where .......)
SET #sql = 'SELECT * into ' + #temptablename + ' FROM (' + #qry + ') A '
It gives some flexibility
Remember that it is easy to check structure of the table created in this way in sys so you can build another #SQL from this info if needed.
I this as well recommended to split "SELECT INTO" to 2 parts
One is
SELECT INTO ......... WHERE 1=2
Second
INSERT INTO SELECT ......
Creation of table locks all DB. So it is good to create it as fast as possible and then insert into it.
I'm wondering if copying an existing Table into a Temporary Table results in a worse performance compared to Dynamic SQL.
To be concrete i wonder if i should expect a different performance between the following two SQL Server stored procedures:
CREATE PROCEDURE UsingDynamicSQL
(
#ID INT ,
#Tablename VARCHAR(100)
)
AS
BEGIN
DECLARE #SQL VARCHAR(MAX)
SELECT #SQL = 'Insert into Table2 Select Sum(ValColumn) From '
+ #Tablename + ' Where ID=' + #ID
EXEC(#SQL)
END
CREATE PROCEDURE UsingTempTable
(
#ID INT ,
#Tablename Varachar(100)
)
AS
BEGIN
Create Table #TempTable (ValColumn float, ID int)
DECLARE #SQL VARCHAR(MAX)
SELECT #SQL = 'Select ValColumn, ID From ' + #Tablename
+ ' Where ID=' + #ID
INSERT INTO #TempTable
EXEC ( #SQL );
INSERT INTO Table2
SELECT SUM(ValColumn)
FROM #TempTable;
DROP TABLE #TempTable;
END
I'm asking this since I'm currently using a Procedure build in the latter style where i create many Temporary Tables in the beginning as simple extracts of existing Tables and am afterwards working with these Temporary Tables.
Could I improve the performance of the stored procedure by getting rid of the Temporary Tables and using Dynamic SQL instead? In my opinion the Dynamic SQL Version is a lot uglier to programm - therefore i used Temporary Tables in the first place.
Table variables suffer performance problems because the query optimizer always assumes there will be exactly one row in them. If you have table variables holding > 100 rows, I'd switch them to temp tables.
Using dynamic sql with EXEC(#sql) instead of exec sp_executesql #sql will prevent the query plan from being cached, which will probably hurt performance.
However, you are using dynamic sql on both queries. The only difference is that the second query has the unnecessary step of loading to a table variable first, then loading into the final table. Go with the first stored procedure you have, but switch to sp_executesql.
In the posted query the temporary table is an extra write.
It is not going to help.
Don't just time a query look at the query plan.
If you have two queries the query plan will tell you the split.
And there is a difference between a table variable and temp table
The temp table is faster - the query optimizer does more with a temp table
A temporary table can help in a few situations
The output from a select is going to be used more than once
You materialize the output so it is only executed once
Where you see this is with a an expensive CTE that is evaluated many times
People of falsely think a CTE is just executed once - no it is just syntax
The query optimizer need help
An example
You are doing a self join on a large table with multiple conditions and some of conditions eliminate most of the rows
A query to a #temp can filter the rows and also reduce the number of join conditions
I agree with everyone else that you always need to test both... I'm putting it in an answer here so it's more clear.
If you have an index setup that is perfect for the final query, going to temp tables could be nothing but extra work.
If that's not the case, pre-filtering to a temp table may or may not be faster.
You can predict it at the extremes - if you're filtering down from a million to a dozen rows, I would bet it helps.
But otherwise it can be genuinely difficult to know without trying.
I agree with you that maintenance is also an issue and lots of dynamic sql is a maintenance cost to consider.