The strategy selected by the query optimiser to process a query.

learn more… | top users | synonyms (1)

4
votes
1answer
108 views

Should I use a subquery to help SQL Server find the correct plan

I have a query (which has components which are built on the fly depending on the selections a user makes in the interface) that runs in SQL Server 2008-R2 that runs in about 100 databases. Users are ...
4
votes
1answer
329 views

SQL Server : parsing with XPath Performance

I have a UI that allows a user to select certain data points they want to filter the results by. There are things such as location, department etc. Once they have selected all of the options, I ...
4
votes
1answer
65 views

DISTINCT ON vs ROW_NUMBER() for getting a row with a maximum value of a group

I have the following table in PostgreSQL 9.4: CREATE TABLE dpa( id serial NOT NULL, currency_id integer, amount numeric(14,3), date timestamp without time zone, plat_id integer, pl_id ...
4
votes
2answers
231 views

SQL Server doesn't use expected index

I have the following query (simplified from an Entity Framework query, I don't have direct control of the SQL): SELECT TOP 15 HouseHoldingRuns.Id, ( SELECT TOP 1 ManCoId FROM ( SELECT TOP ...
4
votes
1answer
1k views

Non-Clustered Index key columns to cover a variable where clause

To whoever reads this, sorry for the long question and thanks so much for your time. I'm needing some help on understanding what columns should be key/non key in the following situation, and what ...
4
votes
1answer
1k views

SQL Server 2008 query planner failing after index drop & recreate

Recently we ran a script to our production DB that would dynamically drop and recreate hundreds of indexes as filtered indexes. While this script had run perfectly in all other previous tests, now ...
3
votes
3answers
1k views

How does NHibernate handle execution plan?

I heard from a podcast that there are no ORMs that have a good solution for execution plan reuse. It will lead to increased execution plan cache which affects the performance. How does NHibernate ...
3
votes
2answers
97 views

When does SQL Server determine to use a new index?

I have been performing some maintenance on a server that runs some software the company bought, so I can't really change how the queries have been written. I have used some tools to determine some of ...
3
votes
1answer
69 views

Aggregation GROUP BY bottleneck

I have a performance bottleneck with a SELECT GROUP BY operation. Schema I have a table like this: CREATE TABLE [InverterData]( [InverterID] [bigint] NOT NULL, [TimeStamp] [datetime] NOT ...
3
votes
2answers
621 views

Use a view to join tables or a stored procedure for a better execution plan?

First let me state I am a C# developer, not a SQL Server DBA, so please excuse my ignorance on SQL Server database query execution plans. What I want to know is for a stored procedure which the ...
3
votes
2answers
154 views

Changing metadata changes query output issue [duplicate]

Recently stumbled across the following problem: changing metadata changes query output. Here is how to get it. CREATE TABLE [dbo].[prod] ( [ID] [tinyint] NOT NULL, [values] [tinyint] NOT NULL ) GO ...
3
votes
1answer
2k views

Clustered Index Update on Nonclustered Columns

Using: SQL Server 2008 R2 I am currently stepping through a query execution plan, and have come across an instance of a clustered index update on a table. The issue here is that the columns that are ...
3
votes
1answer
545 views

How to determine cause of runtime increase given two query plans with SpillToTempDb warning

Two actual query plans were captured for two executions of one query: Plan "Fast" took ~1s and occurs about 90% of the time. Plan "Slow" took ~16s. Since the graphical plans look ...
3
votes
1answer
541 views

sql server partitioned view execution plan questions

I have created a partitioned view for 3 tables tb_sales2010,tb_sales2011,tb_sales2012 using check constraint (respectivly for each table) datepart(year,[Date])=(2010) datepart(year,[Date])=(2011) ...
3
votes
2answers
416 views

Slow fulltext search due to wildly innacurate row estimates

Fulltext queries against this database (storing RT tickets) seem to be taking a very long time to execute. The attachments table (containing the fulltext data) is about 15GB. The database schema is ...
3
votes
1answer
138 views

Do operations on indexed views happen in parallel?

When I'm inserting into a table that has a view with a clustered index, the estimated execution plan appears to do the table insert and the view's clustered index insert operations in parallel. Is ...
3
votes
2answers
172 views

Any SQL where clause performance similar to where 1=0

(i'm using SQL Server 2008R2 or later) For centralize manage and consistent, there is a view definition as follow: CREATE VIEW view_all_situation ( select null as src, tf.col1, sum(col2) as fee, ...
3
votes
1answer
44 views

Execution plan for COMPUTE BY

I understand that the COMPUTE BY feature is deprecated. Out of curiosity I would like to know how the query processor executes a COMPUTE BY query. The execution plan does not contain any hint: How ...
3
votes
1answer
325 views

Trace Flag 4199

Microsoft's KB article about Trace Flag 4199 is a bit confusing: ...any hotfix that could potentially affect the execution plan of a query must be controlled by a trace flag. Except for fixes ...
3
votes
1answer
400 views

SHOWPLAN does not display a warning but “Include Execution Plan” does for the same query

I was running the following query in SSMS and it showed me a warning in the "Include Execution Plan" window select CLIENT_GUID, PMT_AMOUNT, DATE_COMPLETED from ( select payment.CLIENT_GUID, ...
3
votes
2answers
496 views

Multicolumn statistics on large table yielding poor estimations

I have a rather large table (~200 million rows), and although the statistics are up to date using WITH FULLSCAN, is it possible that my histogram (limited to 200 steps) is simply too broad for the ...
3
votes
1answer
115 views

Understanding SQL Server plan cache

I've been reading about the SQL Server plan cache and optimizing for adhoc workloads, etc. I'm fairly new to the topic and have a few general questions to help paint a better picture: Suppose I have ...
3
votes
2answers
3k views

SQL Query too slow on SUM function

I've a table with around 32 million rows having clustered unique index on CountryID,RetailerID,ProductID,DateID,EventID,TypeID and query is SELECT f.RetailerID , TypeID ...
3
votes
2answers
240 views

Query taking too much time

My query is taking too much time to execute. Please help me here. mysql> explain select pcm.catalog_id from cat_produ_catal_map_defer pcm, cat_catal_catal_map_defer ccm, cat_catal_defer c ...
3
votes
1answer
573 views

How are foreign keys resolved when creating tables in batch?

I am creating a database version management tool with the goal of being able to recreate a database from scratch using text/sql files contained in source control. As part of establishing a baseline ...
3
votes
1answer
140 views

Why does my query end up with two seeks instead of one and how do I fix that?

I have these two tables: CREATE TABLE [TaskItems] ( [ItemId] UNIQUEIDENTIFIER NOT NULL UNIQUE PRIMARY KEY, [LastOperationTime] DATETIME NULL DEFAULT GETUTCDATE(), [OwnerId] ...
3
votes
1answer
181 views

How do I deal with query getting slower when a select parameter is not specified inline?

I faced this problem twice with SQL Azure and two different queries so far. Something like this: select top(100) * from SomeView WHERE AccountId='actual-guid-typed-in-here' runs super fast but ...
3
votes
1answer
237 views

Optimizing complex join predicates [closed]

Table Definitions CREATE TABLE [dbo].[Pin_Mtg] ( [MtgId] bigint NULL, [CntyCd] char(5) NOT NULL, [BatchDt] int NOT NULL, [BatchSeq] int NOT NULL, [MtgSeq] tinyint NOT NULL, ...
3
votes
1answer
101 views

PostgreSQL + query planner + amount of entities

I'm working on a college assignment about how the query planner uses statistics and makes the most optimal query plan. I have read the 57.1. Row Estimation Examples article and I know how PostgreSQL ...
3
votes
1answer
55 views

Having hard time understanding expressions in below query plan

I was going through Temporal tables new features in SQL 2016,one of the examples was to query tables with as of clause which returned below query plan Rows Executes StmtText StmtId NodeId ...
3
votes
1answer
3k views

Is there any difference on performance when choosing DISTINCT or GROUP BY to bring distinct values?

I would like to know if there is any difference concerning performance when choosing DISTINCT or GROUP BY to bring distinct rows from a query. I've tried comparing the execution plans, but they seem ...
3
votes
1answer
824 views

Is there any way to get the estimate cost of executing a query in MySQL?

In PostgreSQL, EXPLAIN or EXPLAIN ANALYZE will show the estimate cost of executing a query. But EXPLAIN in MySQL doesn't provide this information. How can I get the estimate cost without installation ...
3
votes
1answer
121 views

Simple SELECT takes forever, but works as a subquery. Why?

I'm running a MySQL 5.1 server and I have a MyISAM table called my_table with nearly 5 million records. Its structure is the following: ...
3
votes
1answer
615 views

Execution plan in simple query in PgSQL depends on offset clause, why?

Update on 2013-01-16 11:08: see below I am working on PostgreSQL 8.4.14 with the following table fed with 53k lines: CREATE TABLE botany.taxon_data_cache ( taxon_id int NOT NULL, ...
3
votes
1answer
1k views

View SQL 2008 sp_cursorexecute Underlying Query and Execution Plan

I'm performance tuning a Dynamics AX application and see in a SQL trace a long-running, high-I/O query of the form exec sp_cursorexecute 1073742882 ... When I try and run that query in a new SQL ...
3
votes
0answers
50 views

Is execution plan cached “better” for stored procedures than for a non-dynamic query?

Reading different explanations about execution plan caching by Microsoft SQL Server, I'm confused about the benefits of using stored procedures instead of non-dynamic queries. By a non-dynamic query ...
3
votes
0answers
95 views

Bad Plan after a couple of days

I have this query that runs fine for a couple of days (from the application) and then slows down to where it can't even finish. If I rebuild the plan, it flies. There is a signifigant amount of data ...
2
votes
2answers
980 views

How can you tell when a query plan reuse is causing performance problems

When investigating a performance issue, a workmate suggested running DBCC FREEPROCCACHE to clear the plan cache. He came to this conclusion after noticing performance improved after a reboot. This ...
2
votes
2answers
113 views

Can I disable execution plan caching for debugging purposes?

I am trying to isolate poor performing queries in our application. While query execution plan caching is great in production it is interfering with our debugging efforts. Is there are way to ...
2
votes
3answers
458 views

Why is the SQL Server query plan not using indexes in a query almost similar to one that uses indexes?

I have two UPDATE queries that are similar in structure, yet the SQL Server query plan for one shows indexes being used, and for the other it shows only a regular table scan. The following are the ...
2
votes
2answers
82 views

On which server does a query execute?

Given two Microsoft SQL servers: Say ServerA has a view titled "View1": SELECT * FROM ServerB.database.dbo.Table1 WHERE Column1 IN (1,2,3) and a stored procedure "sp_Foo": SELECT * FROM View1 WHERE ...
2
votes
1answer
117 views

Execution Plan not matching Stored Proc

Below is a stored proc to count the number of widgets made in a month. If no widgets are made, no records will exists. The execution plan shows an INNER JOIN of the M and A tables, where in the ...
2
votes
1answer
5k views

What I can do to speed up Key Lookup in my Query

I am using SQL2005 and against them I calling query simila to this declare @art table (id int primary key, naziv varchar(35) null, sifra varchar(15) null, jm int null); insert ...
2
votes
1answer
432 views

Does SQL check each And condition if first condition fails? [duplicate]

For a query of below kind does sql process data for each And condition if first And condition fails? If Emp_ID is not 12 for a row then does it check condition of Emp_Name? So how SQL process this ...
2
votes
1answer
269 views

Relative cost of two similar queries involving XML columns

I have two queries as shown below which do the same thing. Here xmlcolumn is a column with datatype XML. I use these queries to search for a string anywhere in the XML column. I checked the execution ...
2
votes
1answer
348 views

How do you figure out what planner cost constants to use in Postgres?

I'm using Postgres 8.4 right now. Performance has started to become an issue as our tables have grown in size and our queries in complexity, so I've started to look into some performance tuning, but I ...
2
votes
3answers
2k views

Why would recompile query hint result in different plan for same adhoc statement after freeproccache?

This is on SQL 2005 SP2, but I suspect this is something that applies to all query hints in general. I've got an adhoc sql statement that gets a different query plan solely because of ...
2
votes
1answer
2k views

How bad is query plan pollution (too many equivalent plans in cache)?

Question currently affects C#/.NET, DB access based on ADO.NET and SQL Server 2008 R2, but I think it applies to other databases as well. I noticed some old modules of a system have non-optimal SQL ...
2
votes
2answers
1k views

Is it correct, order of where clause doesn't matter when it is used with join?

I have question on execution of queries in which join is used with where clauses. I read this question on join with where conditions. I tried options like disabling rules and checked actual query ...
2
votes
1answer
2k views

SQL Server 2008 R2 sys.dm_exec_sql_text question

If i run the following query on our production server: SELECT DISTINCT TOP 10 t.TEXT QueryName, s.execution_count AS ExecutionCount, s.max_elapsed_time / 100000 AS MaxElapsedTime, ...