Use this tag for questions about improving the performance and/or efficiency of database queries.

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8
votes
2answers
366 views

Query 100x slower in SQL 2014, Row Count Spool row estimate the culprit?

I have a query that runs in 800 milliseconds in SQL 2012 and takes about 170 seconds in SQL 2014. I think that I've narrowed this down to a poor cardinality estimate for the Row Count Spool operator. ...
8
votes
1answer
1k views

How to get accurate query performance?

I'm attempting to improve performance of a stored procedure. When I run the SP, it finishes almost instantly, as if something were cached. I was told to use the following two lines of SQL before ...
8
votes
1answer
169 views

Overcome MERGE JOIN(INDEX SCAN) with explicit single KEY value on a FOREIGN KEY

Added 7/11 The issue is deadlocks occur because of index scan during MERGE JOIN. In this case a transaction trying to get S lock on the whole index at the FK parent table, but previously another ...
8
votes
2answers
16k views

High CXPACKET and LATCH_EX waits

I am having some performance issues with a data processing system which I am working on. I have gathered wait stats from a one hour peroid which show a large amount of CXPACKET and LATCH_EX wait ...
8
votes
1answer
464 views

What does duration measurement in sql server actually measure?

What precisely does the query duration measure when conducting a profiler trace? I have a stored procedure which performs data access (SELECT), and it is taking an average of around 30 seconds to ...
8
votes
1answer
293 views

Update queries slower after enabling SQL Server Full-Text Index

I have an asp.net website with many insert, update, and delete queries running against my database. A few days ago I create a Full-Text Index on two columns of one of tables. After that I realized ...
7
votes
4answers
7k views

What can speed up a SQL count query?

When doing a count (aggregate) SQL query, what can speed up the execution time in these 3 database systems? I'm sure many things could speed it up (hardware for one), but I'm just a novice DBA, so ...
7
votes
3answers
317 views

How can I identify when to create a new table to hold data that can be obtained from a query?

We have a payment table, and agents get commission on payments. Commission is based on a few different factors, such as how long it took to get the payment, so there is some calculations involved when ...
7
votes
1answer
316 views

Better execution plan if parameter is stored in local variable

I have two stored procedures. This one is incredibly fast (~ 2 seconds) CREATE PROCEDURE [schema].[Test_fast] @week date AS BEGIN declare @myweek date = @week select distinct serial ...
7
votes
1answer
263 views

Query optimizer recommends adding index instead of using existing index

I am trying to determine why the query optimizer in SQL Server is recommending creating a new index instead of using an existing index that appears to be sufficient for the query. First the table. ...
7
votes
4answers
1k views

Gaps and islands: client solution vs T-SQL query

Can a T-SQL solution for gaps and islands run faster than a C# solution running on the client? To be specific, let us provide some test data: CREATE TABLE dbo.Numbers ( n INT NOT NULL ...
7
votes
6answers
4k views

Recommendations for MS SQL Server monitoring software or service? [closed]

I have a client with MS SQL Server instances (2000, 2005) scattered across 20-30 servers. I've been engaged to get things organized and will be periodically reviewing the state of the database ...
7
votes
1answer
1k views

Query is slow in SQL Server 2014, fast in SQL Server 2012

During the migration of one of our databases from SQL Server 2012 (SP1, CU2) to SQL Server 2014 (SP1), we have experienced some strange issues. One of the queries that completes within seconds on SQL ...
7
votes
1answer
2k views

Estimated vs Actual rows differences (actual much smaller than estimated) - sort

I'm running a query that is processing some nodes out of an XML document. My estimated subtree cost is in the millions and it seems it all comes from a sort operation sql server is performing on some ...
7
votes
1answer
525 views

How do I prevent a massive SELECT from blocking other statements?

Our SQL Azure database contains a massive SELECT statement that runs something like once per day. The heavy SELECT statement contains no locking hints. Recently we observed some stalls in production ...
7
votes
1answer
767 views

Sargable Queries

Very simple question I hope, I'm currently having some scripts I inherited into my project reviewed by the database admins. This has never been done before apparently and lots of issues are being ...
7
votes
2answers
5k views

An efficient way to compare two large data sets in SQL

Currently, I'm comparing two data sets, that contain unique StoreKey/ProductKey combinations. The 1st data set has the unique StoreKey/ProductKey combinations for sales between begin January 2012 and ...
7
votes
1answer
264 views

How should we handle rows which won't be queried once they are old in PostgreSQL?

We have a table in a PostgreSQL database which is growing on the order of millions of rows per day. Each row consists of: ID Foreign user ID Date and time Other data The date and time aren't ...
7
votes
1answer
8k views

OPTION FORCE ORDER improves performance until rows are deleted

I have a somewhat complex SQL Server 2008 query (about 200 lines of fairly dense SQL) that wasn't performing as I needed it. Over time, performance dropped from about .5 seconds to about 2 seconds. ...
7
votes
1answer
86 views

how come a table variable is improving the performance of a query in this circumstance?

for this specific case, that I will try to explain below, using a table variable is performing better than not using a table variable. I would like to know why, and if possible, get rid of the table ...
7
votes
3answers
10k views

PostgreSQL Sequential Scan instead of Index Scan Why?

Hi All I've got a problem with my PostgreSQL database query and wondering if anyone can help. In some scenarios my query seems to ignore the index that I've created which is used for joining the two ...
7
votes
1answer
154 views

Query against sys.schemas and sys.synonyms runs very slow for one user

Scenario: SQL Server 2014 (v12.0.4100.1) .NET Service runs this query: SELECT name, base_object_name FROM sys.synonyms WHERE schema_id IN (SELECT schema_id FROM sys.schemas ...
7
votes
1answer
158 views

Lead/Lag Implementation in SQL Server 2008 R2: Max memory exceeded

Background I'm trying to establish a "visits" sequence, wherein if an animal is detected at essentially the same place (General_Location) it counts as a single visit, but if it goes elsewhere and ...
7
votes
2answers
188 views

Finite State Machines in SQL

I'd like some input on an issue I'm having. We have a section of code that we repeat throughout our stored procedures, and every time it takes quite some time to process, and when combined the number ...
7
votes
1answer
136 views

Improving a DbGeography query

I am still new to database administration and I'm trying to optimise a search query. I had a query which looked like this and took 5-15 seconds to execute in some cases, and also was causing 100% CPU ...
7
votes
0answers
106 views

SQL Server - Handling localization of strings in nested non-deterministic view stacks

While profiling a database I came across a view that is referencing some non-deterministic functions that get accessed 1000-2500 times per minute for each connection in this application's pool. A ...
6
votes
3answers
6k views

Query runs slow in test site on first execution. Why?

I found this query by watching a test site with sql profiler for anything taking over 10 seconds. I plopped the code right out of sql profiler and into sql studio, where it was able to execute ...
6
votes
3answers
19k views

How to make multiple counts in one query?

I count records with queries like SELECT COUNT(col1) FROM table1 WHERE col1 LIKE '%something%' SELECT COUNT(col1) FROM table1 WHERE col1 LIKE '%another%' SELECT COUNT(col1) FROM table1 WHERE col1 ...
6
votes
3answers
340 views

Which is the most efficient way to run a particular select query?

If I run the following code: select PolicyNumber, MAX(decpageid) as decpageid, Risk from StatRiskDecpages where PolicyNumber = 'AR-0000301132-04' group by PolicyNumber, Risk I get the following ...
6
votes
2answers
5k views

GROUP BY with MAX versus just MAX

I am a programmer, dealing with a big table which the following scheme: UpdateTime, PK, datetime, notnull Name, PK, char(14), notnull TheData, float There is a clustered index on Name, UpdateTime ...
6
votes
3answers
354 views

The fastest way to get the most recent records [duplicate]

I am looking for the fastest way to return the most recent record for each reference number. I quite liked the solution from BrentOzar.com, but it does not seem to work when I add a third condition ...
6
votes
2answers
1k views

Parameter Sniffing: Why Does This Become An Issue?

Today, I had an issue with a SPROC Timing Out (took longer than 30 seconds) when it was run from an ASP.NET webpage, but executed quickly when run from SSMS (took 5 seconds). After suspecting ...
6
votes
2answers
175 views

Hindrance in TSQL SVF Call

I have a simply Products data table with 100k records (just generates some random data): set nocount on create table dbo.temp_Products ( [ProductID] int, [Type] tinyint, [Price] float, ...
6
votes
2answers
237 views

Is there a SQL Server implementation of the Longest Common Substring problem?

Is there a SQL Server implementation of the Longest Common Substring problem? A solution that checks with all rows of a column in SQL Server? I have seen solutions that take two strings as input, but ...
6
votes
3answers
12k views

GROUP BY one column, while sorting by another in PostgreSQL

How can I GROUP BY one column, while sorting only by another. I'm trying to do the following: SELECT dbId,retreivalTime FROM FileItems WHERE sourceSite='something' GROUP BY seriesName ...
6
votes
1answer
1k views

Index seek much slower with OR condition compared with separate SELECTs

Based on these questions and the answers given: SQL 2008 Server - performance loss possibly connected with a very large table Large table with historical data allocates too much of SQL Server 2008 ...
6
votes
3answers
92 views

Query wont compile/run

I have a query that won't run on the production server but it runs on the test server. It seems like the query plan won't compile or its compiling a very bad query plan. I have updated all statistics ...
6
votes
2answers
522 views

Effect of an index on update statements where update column is not in an index

I constantly see people say that indexes slow down update, delete and insert. This is used as a blanket statement, as if it is an absolute. While tuning my database to improve performance, I keep ...
6
votes
2answers
321 views

Unexpected Implicit conversion in a procedure

I have a procedure like this (simplified): CREATE PROCEDURE test @userName VARCHAR(64) SELECT * FROM member M INNER JOIN order O ON M.MemberId=O.MemberId WHERE M.Username = @userName There is a ...
6
votes
1answer
263 views

How to Optimise Query

I have a database structure similar to this, CREATE TABLE [dbo].[Dispatch]( [DispatchId] [int] NOT NULL, [ContractId] [int] NOT NULL, [DispatchDescription] [nvarchar](50) NOT NULL, ...
6
votes
2answers
7k views

How can I improve the speed of a query on a 20 million+ row table?

I have a query that is used for getting internet traffic statistics of certain IP addresses. There are separate IP address fields for hosts and blocks of IPs called assignments. The data is stored ...
6
votes
1answer
2k views

Does the order of columns has a significant effect on INSERT?

Do we experience a noticeable difference in performance for these two queries? INSERT INTO table (col1, col2, col3, col4, col5) ... and INSERT INTO table (col5, col3, col1, col2, col4) ... Do we ...
6
votes
3answers
324 views

Convert date in date list condition to list of date ranges

I want to look for all the records that occur on specific dates. SELECT * FROM table1 WHERE date(column) in ($date1, $date2, ...); However, as many of you, know this kind of comparison doesn't get ...
6
votes
2answers
231 views

Clustered Table Scan Because of “SELECT *”

I have a Records table with over 100 columns and very many rows, and a nonclustered index on 5 fields based on my access paths: CREATE NONCLUSTERED INDEX [IX_Records_CustomerID] ON [dbo].[Records] ( ...
6
votes
2answers
11k views

Learning to Optimize SQL Queries and Understand Execution Plans - Resources?

I find myself writing more and more SQL queries at work (mostly Oracle 11g, but some SQL Server 2005-2008) and have started creating some pretty complex views for the rest of the analyst team. They ...
6
votes
2answers
2k views

Why does MySQL choose this execution plan?

I have two queries, select some_other_column from `table` order by primary_index_column asc limit 4000000, 10; and select some_other_column from `table` order by secondary_index_column asc ...
6
votes
3answers
283 views

Slow query performance due to temporary file?

Here is the query: SELECT "products".* FROM "products" WHERE (status > 100) AND "products"."above_revenue_average" = 't' AND ("products"."category_id" NOT IN (5)) ORDER BY ...
6
votes
2answers
1k views

Filter table before join

I have a stored procedure that populates the temp table #employee_benefits with a list of Ids. This table ends up being roughly 10,000 rows long. The query below then selects from a table called ...
6
votes
1answer
245 views

Is it recommended to clear the query plan cache

Pretty much as the title describes. I have just checked a SQL Server and noticed there is a lot of query plan bloat that can be fixed by proper parametrisation. After making the changes to the code, ...
6
votes
1answer
9k views

Comparing two queries in SQL Server 2012

I am comparing two queries in SQL Server 2012. The goal is to use all of the pertinent information available from the query optimizer when choosing the best query. Both queries produce the same ...