I am working on a project where I came across on a sql query. I want see the execution flow fully. i.e how the query executed on database. what can I do for this?
can any body help me for this?
Atomic Operations
The query will be an atomic operation so that you could set table A.Description = table B.Description without having to worry about overwriting the data from either table.
A great book on sql querying -The book that you need to read is Inside Microsoft® SQL Server® 2008: T-SQL Querying. This will show you exactly how a query is processed. You can also use Display Estimated Execution Plan / Show Actual Execution Plan setting in sql server management studio to see a visual plan. You can right click the query pane to toggle them on and off. You will have to figure out how to read it first.
Actual Order of query based on Itzak Ben-Gan in the book.
1 FROM
2 ON <join_condition>
3 <join_type> JOIN <right_table>
4 WHERE <where_condition>
5 GROUP BY <group_by_list>
6 WITH { CUBE | ROLEUP }
7 HAVING <having_condition>
8 SELECT
9 DISTINCT
10 ORDER BY <order_by_list>
11 TOP
Related
I am running a db2 query that unions two very large tables. I started the query 10 hours ago, and it doesn't seem to finish yet.
However, when I check the status of the process by using top, it shows the status is 'S'. Does this mean that my query stopped running? But I couldn't find any error message.
How can I check what is happening to the query?
In DB2 for LUW 11.1 there is a text-based dsmtop utility that allows you to monitor the DB2 instance, down to individual executing statements, in real time. It's pre-11.1 equivalent is called db2top.
There is also a Web-based application, IBM Data Server Manager, which has a free edition with basic monitoring features.
Finally, you can query one of the supplied SQL monitor interfaces, for example, the SYSIBMADM.MON_CURRENT_SQL view:
SELECT session_auth_id,
application_handle,
elapsed_time_sec,
activity_state,
rows_read,
SUBSTR(stmt_text,1,200)
FROM sysibmadm.mon_current_sql
ORDER BY elapsed_time_sec DESC
FETCH FIRST 5 ROWS ONLY
You can try this command as well
db2 "SELECT agent_id,
Substr(appl_name, 1, 20) AS APPLNAME,
elapsed_time_min,
Substr(authid, 1, 10) AS AUTH_ID,
agent_id,
appl_status,
Substr(stmt_text, 1, 30) AS STATEMENT
FROM sysibmadm.long_running_sql
WHERE elapsed_time_min > 0
ORDER BY elapsed_time_min desc
FETCH first 5 ROWS only"
Using crystal reports version 14, MS sql server 2008
I am joining two tables and I need to filter in the join, so if a certain value exists in one of the table, I want to join to that record, if it does not exist, I want to have a null-record. I.e:
select * from sample left outer join test
on(sample.sample_number=test.sample_number and test.name='PREP')
I can run that in Sql server studio and get exactly what I want
What I can get in crystal reports is
select * from sample left outer join test
on(sample.sample_number=test.sample_number)
where test.name='PREP'
In the latter case, rows where test.name='PREP' does not exist will be removed and if there are samples that have no test.name='PREP', those samples will be removed.
Are there any ways I can do this in CR 14?
dummy tables:
Sample
sample_number,name
1,A
2,B
3,C
Test
sample_number,name
1,PREP
1,SOMETHING
2,SOMETHING
3,SOMETHING_ELSE
3,PREP
What I want:
1,A,1,PREP
2,B,NULL,NULL
3,C,3,PREP
(of course there are more fields in the tables and a selection of which fields, but this should illustrate what I want)
I know I can make views and query them directly in crystal, but if possible, I would avoid doing that.
Bah, found it:
Database expert - add table, select data source, add command. Then a custom sql can be added.
I have some performance issue in this case:
Very simplified query:
SELECT COUNT(*) FROM Items WHERE ConditionA OR ConditionB OR ConditionC OR ...
Simply I have to determine how many Items the user has access through some complicated conditions.
When there is a large number of records (100,000+) in the Items table and say ~10 complicated conditions concatenated in WHERE clause, I get the result about 2 seconds in my case. The problem is when a very few conditions are met, f.e. when I get only 10 Items from 100,000.
How can I improve the performace in this "Get my items" case?
Additional information:
the query is generated by EF 6.1
MS SQL 2012 Express
SQL Execution Plan
Add an additional table to your schema. Instead of building a long query, insert the value for each condition into this new table, along with a key for that user/session. Then, JOIN the two tables together.
This should perform much better, because it will allow the database engine to make better use of indexes on your Items table.
Additionally, this will position you to eventually pre-define sets of permissions for your users, such that you don't need to insert them right at the moment you do the check. The permission sets will already be in the table, and the new table can also be indexed, which will improve performance further.
2 stored procedures are developed by .net developers. which are giving same record counts when you pass the same parameter?
now due to some changes , we are getting mismatch record count i.e
if first stored procedure is giving 2 records for a paramemter , the second SP is giving only 1 record.
to find this i followed the approach like
i verified
i counted total records of a table after joining
total tables used in joining
3.distinct / group by is used in 2 tables or not?
finally i am not able to find the issue.
how do i fix it?
could any body share some ideas.
thanks in advance?
Assuming the same JOINs and filters, then the problem is NULLs.
That is, either
A WHERE clause has a direct NULL comparison which will fail
A COUNT is on a nullable column. See Count(*) vs Count(1) for more
Either way, why do you have the same very similar stored procedures written by 2 different developers, that appear to have differences?
I butter-fingered a query in SQL Server 2000 and added a period in the middle of the table name:
SELECT t.est.* FROM test
Instead of:
SELECT test.* FROM test
And the query still executed perfectly. Even SELECT t.e.st.* FROM test executes without issue.
I've tried the same query in SQL Server 2008 where the query fails (error: the column prefix does not match with a table name or alias used in the query). For reasons of pure curiosity I have been trying to figure out how SQL Server 2000 handles the table names in a way that would allow the butter-fingered query to run, but I haven't had much luck so far.
Any sql gurus know why SQL Server 2000 ran the query without issue?
Update: The query appears to work regardless of the interface used (e.g. Enterprise Manager, SSMS, OSQL) and as Jhonny pointed out below it bizarrely even works when you try:
SELECT TOP 1000 dbota.ble.* FROM dbo.table
Maybe table names are constructed from a naive concatenation of prefix and base name.
't' + 'est' == 'test'
And maybe in the later versions of SQL Server, the distinction was made more semantic/more rigorously.
{ owner = t, table = est } != { table = test }
SQL Server 2005 and up has a "proper" implementation of schemas. SQL 2000 and earlier did not. The details escape me (its been years since I used SQL 2000), all I recall clearly is that you'd be nuts to create anything that wasn't owned by "dbo". It all ties into users and object ownership, but the 2000 and earlier model was pretty confusticated. Hopefully someone will read up on BOL, do some experimentation, and post their results here.
S-SQL reference manual:
"[dot] Can be used to combine multiple names into a name of the form A.B to refer to a column in a table, or a table in a schema. Note that you calso just use a symbol with a dot in it."
So I think if you referenced tblTest as tblT.est it would work OK as long as there isn't a column called 'est' in tblTest.
If it can't find a column name referenced with the dot I imagine it checks the parent of the object.
I found a reference to it being a bug
Note: as a result of a comparison
algorithm bug in SQL Server 2000, dot
symbols themselves have no effect on
matching, so "dbo.t" will successfully
match with tables "dbot", "d.b.o.t",
etc
from Link
It's been fixed in SQL Server 2005. Same link > Changes introduced in SQL Server 2005
Dot-related comparison bug has been fixed.
Is it in the "Open table" view of SSMS or via Enterprise Manager or via an SSMS Query Window?
There is/was a SQL Server 2005 issue with SSMS so how you run the query affects how it behaves.
This is a bug.
It has to do with internal representation of column names in SQL server 2000 that leaked out.
You will also not be able to create tablecolumn with a name which collides with table+column concatenation with another column, like, if you have tables User and UserDetail, you won't be able to have columns DetailAge and Age in these tables, respectively.