A class of issues where a database executes a query inefficiently due to the optimiser selecting an innapropriate query plan.

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2
votes
2answers
210 views

DISTINCT not using an index [duplicate]

I have table (2139868 rows): COLUMN1 NUMBER(20,0) COLUMN2 XMLTYPE COLUMN3 XMLTYPE COLUMN4 VARCHAR2(50 BYTE) COLUMN5 VARCHAR2(50 BYTE) COLUMN6 VARCHAR2(50 BYTE) COLUMN7 VARCHAR2(50 BYTE) COLUMN8 ...
2
votes
4answers
1k views

Remove sub-string from WHERE clause

I have a stored procedure that is using the SUBSTRING function in the WHERE clause. SELECT DISTINCT ColumnBB, ColumnCC FROM TableAA WITH (NOLOCK) WHERE SUBSTRING(ColumnAA, 1, 17) = @VariableA; ...
2
votes
2answers
223 views

Get table name from union query?

This is my query SELECT Id, productName, Largeimagepath, Discount, Price, Image FROM tablename1 where Active =1 union SELECT Id, productName, Largeimagepath, Discount, Price, Image FROM tablename2 ...
2
votes
3answers
262 views

selecting multiple instances of a record based on record lifespan over years

I have a table of items that have a origin date and a life span. I want to create a procedure that selects all of the items that will need to be replaced in a specific duration. I feel like there is a ...
2
votes
2answers
169 views

What can be done to further enhance performance of Multiple Join and Aggregate Queries?

I have a typical star schema simulated here, and I am mentioning two queries: first query simply joins the fact table with 2 dimension tables and 1 calendar table, and the second query joins and ...
2
votes
2answers
99 views

which option is better for not slow down the performance of queries?

I am developing a system that records customer payments, when a customer makes a payment, the system must update the account and show the payment made and all previous payments, is here when the ...
2
votes
1answer
226 views

Why is the following query so bad performance-wise

After asking this question, I got to thinking about why a certain query was doing all the problems. In short, there was a query which took 500ms, I ran some execution plans and applied the ...
2
votes
3answers
269 views

mariadb ignoring force index

I'm trying to tune a relatively simple query: select bt.col1,bt.col2 from bigtable bt join smalltable st on bt.smalltable_id = st.smalltable_id where st.name = 'some name occuring only once in st' ...
2
votes
1answer
150 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
2answers
84 views

Comparing Queries

In SQL Server, if you're comparing the statistics IO from two queries, how do you ensure that caching doesn't become a factor? For example (I'm making this up as I type, not a real example): SELECT ...
2
votes
1answer
102 views

Getting each status change in a table

I have a table that holds status changes per item. The item can go in and out of a status multiple times. ItemTable (ItemId int, Status varchar(50), DateOfChange date) I need to pull the date of ...
2
votes
2answers
4k views

Get username and/or IP address responsible for a query

I use the following query to find performance improvements in queries: SELECT TOP 20 SUBSTRING(qt.text, (qs.statement_start_offset/2)+1, ((CASE qs.statement_end_offset WHEN -1 THEN ...
2
votes
2answers
205 views

Changing ORDER BY direction causes performance issue

I use MySQL 5.6, and I have two tables each with 16M rows: CREATE TABLE IF NOT EXISTS `newsstudios` ( `id` int(11) NOT NULL AUTO_INCREMENT, `title` varchar(255) COLLATE utf8_unicode_ci NOT NULL, ...
2
votes
1answer
262 views

Optimize simple query in SQL Server

This should be a quite easy query, but I honestly think its execution time can be improved. select idTag,MAX(pctimestamp) AS PCTIMESTAMP,getdate() AS NOW, datediff(SECOND,MAX(pctimestamp),getdate()) ...
2
votes
2answers
3k views

Will altering order of columns in GROUP BY affect performance?

I have a SQL query like this: SELECT A, B, (CASE WHEN C=0 THEN 0 ELSE 1 END), COUNT(D) FROM SomeTable GROUP BY A, B, (CASE WHEN C=0 THEN 0 ELSE 1 END) On a huge dataset the actual execution plan ...
2
votes
2answers
211 views

UPDATE query with JOIN taking forever

I'm not very good with databases so please keep in mind even if the solution sounds like something everyone would have already tried, please post it because I likely have not tried it and it would ...
2
votes
2answers
385 views

Query hangs forever at first but works after one day

I have two schemas namely A and B. I regularly copy contents of 10 tables from A to B. Here's is how I do it First I rename the original tables in schema B Then, using SQL Developer I copy the table ...
2
votes
2answers
343 views

Improve CTE performance

is there a way to improve the performance of a recursive CTE like below, I am unsure if I can add indexes on joins when the joins are using ROW_NUMBER? DECLARE @File_Name VARCHAR(8000), @Disk ...
2
votes
2answers
676 views

Why does my query run faster after I force full table scan?

I have a MERGE statement that took forever to execute the select as the table it is running from (SUB_DATA) is rather big (read 1.4 Tb, 700 million rows). My SELECT looks like this. SELECT ...
2
votes
1answer
155 views

Need some help with this query get all status and their associated comments of me and all my friends

I've several days dealing with this query but can't get it to works as I want. This post is related to this one Several values from different tables in which I tough found the solution but I was ...
2
votes
3answers
2k views

Is it normal to use many Triggers?

I have many so-called summary columns throughout my database to count number of rows in other tables. For example, counting the number of comments by a user (a column in the user table). Currently, I ...
2
votes
3answers
124 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 ...
2
votes
2answers
970 views

Optimized query to fetch a record from 10 million entries

A table has 2 fields | UniqueKey | TimeStamp | ------------------------- | xfsddddq | 1024125412 | | xfstttdx | 1024125413 |< | xfsdxxau | 1024125415 | Estimated, there are 10 million ...
2
votes
1answer
1k views

Query taking non-consistent time to execute [closed]

I have a query which takes large time to execute sometimes.When i checked the speed it was taking 15 seconds.But actually it should run faster than that.When i again checked the query it again ...
2
votes
2answers
141 views

Different queries result in big difference in performance

I have 2 similar functions, different way result in big diff in performance. The PostgreSQL version: 9.2.1. Function 1 create or replace function func_1() returns text as $$ declare v_i ...
2
votes
2answers
675 views

Slow MySQL query with Order and Group by

I have a query that is taking a long time to execute (1.13s). The two tables user_articles and articles have around 25,000 records. This is the query: SELECT `user_articles`.* FROM `user_articles` ...
2
votes
1answer
103 views

Slow Query Gets Even Slower After Indexing

I have a MySQL database with just one table containing 8 million records. I need to query the table to find a single record that matches a specific number: select * from my_table where ...
2
votes
1answer
1k views

how to improve query performance

## Only 1 query which returns 10 rows. ## It took about 66 secs mysql> explain SELECT al.log_id , al.user_id , al.page_name , al.section_name , al.submit_time , al.url , ...
2
votes
1answer
124 views

How to know what to investigate and how for a VERY slow stored procedure

I have inherited a large and slow stored procedure and it's giving me a nightmare: I'm not a DBA, although I have some knowledge, but I don't know where to start to identify this bottleneck. I have ...
2
votes
1answer
206 views

Why are my queries getting really slow?

I own a WordPress installation, and Updated to 3.4.1. After the upgrade, I experienced a very strange slow-down. After all, I used the define('SAVEQUERIES', true); in my wp-config.php with ...
2
votes
1answer
121 views

Where to place non clustered index

Execution plan clearly showing that one of my table used in query is useing Clustered Index Scan. From this node, how can i guess that which columns should be part of my non clustered index key and ...
2
votes
3answers
236 views

How to get all non deleted messages from one user

I have two tables one for messages called default_messages and the other for recipients called default_recipient. This is how SQL for those table looks like: CREATE TABLE IF NOT EXISTS ...
2
votes
2answers
779 views

How expensive are SELECT FROM LIKE statements from a design perspective?

I have a situation running out of control regarding an ever increasing number of small static files I need to access randomly in a large directory structure. I MUST reduce the number of those files ...
2
votes
1answer
255 views

Oracle ash report

Recently, i have been handed over with an ash report from DBA. To me this report is like french. I have no idea what it is about and what all is written in this report. Can someone please guide me in ...
2
votes
2answers
47 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 ...
2
votes
1answer
52 views

How to optimise window queries in postgres

I have the following table with approximately 175k records: Column | Type | Modifiers ...
2
votes
1answer
114 views

Select data based on records created_at column

I have two tables Keywords, ProjectReports: http://sqlfiddle.com/#!15/06ae3/1 As you can see in that example everything works fine, but I want to get more data from those 2 tables and I don't know ...
2
votes
1answer
181 views

Why would a query in code be slower than a query in a SQL tool

When we face performance issues with out application, one of the first things we do is try to isolate if the problem is the code, the queries or the database itself. The most frustrating part of this ...
2
votes
2answers
936 views

Is there a difference in performance between @date and getdate()?

Usually I use the getdate() function in my where clauses to go back in time. Something like: DOC.DATUM >= DATEADD(DD,-1*SSN_SDO.DANA_ZA_POVRAT,GETDATE()) Will SQL Server 2008R2 perform faster ...
2
votes
1answer
184 views

Parameter triggers different execution plan, but why?

I have a table CREATE TABLE [dbo].[Numbers] ( [Date] [date] NULL, [Time] [time](3) NULL, [Value] [char](10) NULL ) and the table has > 10 Billion rows, therefore it ...
2
votes
2answers
157 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 ...
2
votes
1answer
855 views

How to speed up mysql query?

I have query : SELECT `school`.`ARCO_name`, `student-`.`ClassSize_7`, `student-`.`ClassSize_8`, `degree_o`.`degree_code`, `accredit`.`full_faculty_3`, ...
2
votes
2answers
115 views

Super simple mysql query taking too long

I have the following: SELECT * FROM autorepair WHERE zip_code IN (91316,91356,91416,91426,91436) AND specialty = 'transmission' ORDER BY ABS(91316 - `zip_code`) LIMIT 0,10 Indexes: -zip_code ...
2
votes
1answer
108 views

Query returning unused stored procedures

When I run SP_askbrent@asof = '2014-05-20 16:00' a period where the database was timing out, I'm getting dozens of CREATE PROCEDURE xxx entries. When I run the following query, the results show the ...
2
votes
1answer
36 views

Will composite indexes or unique indexes help with query performance?

I need help with identifying indexes to increase performance of the following query. I'm currently using v5.5 with InnoDB. I cannot modify the query. However, I can add indexes as needed. The ...
2
votes
1answer
36 views

General purpose view for last value in a group

I am trying to create a view to show the last value in the group. Looking for a more general purpose query. CREATE TABLE a ( id INTEGER, seq INTEGER, val VARCHAR2(16), PRIMARY ...
2
votes
2answers
112 views

Convert to Self JOIN

I have a correlated sub query, which is taking 16 Minutes to execute. How can I convert it to join or optimize it. SELECT SSF.SM_StockCode, SSF.ST_ItemSize FROM Stock AS SSF WHERE ...
2
votes
2answers
246 views

Trigger update does not seem to finish

I'm new to PostgreSQL triggers & functions and such. I've got a table: keywords and each keyword should be unique. So when I try to insert a keyword that already exists, it should simply update ...
2
votes
1answer
105 views

Are there differences in performance of getting data between FullText Search and indexed columns

In SQL Server 2008 R2 I have a query which looks like create stored procedure give_me_art @filter varchar(15),@skl_id int begin select id,naziv,sifra,isnull(lager.kolicina,0) as lager from art ...
2
votes
1answer
502 views

inner join on PK with extra criteria slow despite indices?

Given the two tables below I am struggling to understand: why is the third query slow even though first two queries are fast what exactly is EXPLAIN saying can I do anything to significantly speed ...