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14
votes
4answers
12k views

Why are NULLs sorted first?

Why is it that when we have a NULL value in a column and we order by the value ascending, the NULLs are sorted first? select 1 as test union all select 2 union all select NULL union all select 3 ...
13
votes
2answers
658 views

Paging performance with customizable sorting over many millions of rows

In our application we have a grid where users can page over a large number of records (10-20 million). The grid supports sorting in ascending and descending order in a number of columns (20+). Many of ...
11
votes
1answer
6k views

How to preserve the original order of elements in an unnested array?

Given the string: 'I think that PostgreSQL is nifty' I would like to operate on the individual words found within that string. Essentially, I have a separate from which I can get word details ...
8
votes
4answers
1k views

Is there a collation to sort the following strings in the following order 1,2,3,6,10,10A,10B,11?

I have a database with a VARCHAR column that contains integers of varying length. I want to sort them so 10 comes after 9, not 1, and 70A comes after 70. I was able do this with PATINDEX(), a CTE, and ...
8
votes
5answers
6k views

Oracle sort varchar2 column with special characters last

How can I sort in Oracle a Varchar2 or NVarchar2 column to be in my own custom defined order. Or are any existing options available that will put letters first, then numbers, then all special ...
7
votes
4answers
10k views

Slow query on large table with GROUP BY and ORDER BY

I have a table with 7.2 million tuples which looks like this: table public.methods column | type | attributes --------+-----------...
6
votes
5answers
570 views

SQL queries to only show most recent purchase records for individual food items

I'm working with a food purchasing / invoice system in MS Access 2013 and am trying to create an SQL query that will return the most recent purchase price for each individual food item. Here is a ...
6
votes
1answer
2k views

Storage order vs Result order

This is a spin-off question from Sort order specified in primary key, yet sorting is executed on SELECT. @Catcall says this on the subject of storage order (clustered index) and the output order ...
6
votes
1answer
94 views

Why is DistinctSort followed by TopNSort in my query plan?

I have the following definition: CREATE TABLE [dbo].[JobItems] ( [ItemId] UNIQUEIDENTIFIER NOT NULL, [ItemState] INT NOT NULL, [ItemCreationTime] DATETIME ...
5
votes
1answer
224 views

ORDER BY and comparison of mixed strings of letters and numbers

We need to do some reporting on values that are usually mixed strings of numbers and letters that need to be sorted 'naturally'. Things like, e.g. "P7B18" or "P12B3". @The strings will mostly be ...
5
votes
2answers
125 views

Algorithmic order of table indexes for table operations

I have not been able to find a clear indication of the impact table indexes have on the algorithmic order of table operations. I am not interested in the nuts & bolts of specific implementations; ...
5
votes
1answer
738 views

Execution plan using B+ tree index, but also sorts

I'm using Oracle sqlplus. And I have the following query: SELECT fooID from foo MINUS SELECT fooID from bar; I have created two unclustered B+ tree indexes. One in the field fooIDof the table foo ...
4
votes
2answers
235 views

Oracle sort order changed

We recently deployed a new environment with a newer version of Oracle (12c) instead of 11r2. Only recently I noticed my data returned is sorted differently. Instead of having small letters, capital ...
4
votes
5answers
16k views

How to determine the optimal sort_buffer_size?

I read from a sample configuration file which says the following: # Sort buffer is used to perform sorts for some ORDER BY and GROUP BY # queries. If sorted data does not fit into the sort buffer, a ...
4
votes
1answer
145 views

Are two indexes needed?

Our MySQL database will contain an encyclopedia. The encyclopedia will be shown in pages where every page contains entries starting from a letter. Which indexes should I use? Should I have two ...
3
votes
3answers
773 views

How to ORDER BY typical software release versions like X.Y.Z?

Given a "SoftwareReleases" table: | id | version | | 1 | 0.9 | | 2 | 1.0 | | 3 | 0.9.1 | | 4 | 1.1 | | 5 | 0.9.9 | | 6 | 0.9.10 | How do I produce this output? | id | ...
3
votes
1answer
4k views

How can I tell if an index is being used to sort in MySQL?

I have a query with an ORDER BY clause which uses a column which is the last column on an index which is being used in the WHERE clause, essentially of the form: SELECT cols FROM tables WHERE ...
3
votes
2answers
4k views

Postgres primary key sorted in the reverse order. Will it use the index efficiently?

My Rails database is backed by Postgres database. As you may know, each table in Rails gets assigned a primary key which is of Integer type and is indexed. My list views show records in the reverse ...
3
votes
1answer
1k views

MongoDB geospatial query with sort - performance issues

I have query (which is very slow ~2,5s): db.markers.find({ latlng: { '$within': { '$box': [ [ -16, -140 ], [ 75, 140 ] ] } } }).sort({_id: -1}).limit(1000) When I run explain for this query I get {...
3
votes
0answers
87 views

Sort operation SQL Server 2012

I am trying to optimize a query and the sort operation (91% cost) is the costliest operation. Any help will be appreciated. Query is : SELECT TOP 1 ArchiveType, CONVERT(NVARCHAR(30), A....
2
votes
2answers
78 views

Very tricky: Can't update a sequential list SQL-92 ( Filemaker)

I have a quite simple problem, but the solution is very tricky. I'm trying to solve this for months: There is a column "SortID" that needs to get updated with sequential integers, starting from 1. ...
2
votes
1answer
196 views

Threshold for sort spill and random cardinality estimates

I wanted to test tempdb spill warnings so I run the following script on SQL Server 2014: USE tempdb IF OBJECT_ID('tempdb..tblTest') IS NOT NULL DROP TABLE tblTest CREATE TABLE tblTest ( ...
2
votes
1answer
4k views

Order by alphabet and then by numbers

I have records like A5 A4 Z1 B2 C7 C1A C11A B1 B4 I want them to be sorted in this manner A4 A5 B1 B2 B4 C1 C11A C7 Z1 using the ORDER BY clause. I want them to be sorted by alphabets ...
2
votes
1answer
382 views

Index strategy for a Queue Table, getting rid of filesort

I am trying to get rid of a filesort operation (and preferably also optimize a bottleneck query). We are using an innodb mysql table as a queue to process various incoming business activities. It is ...
2
votes
1answer
950 views

how to use index to speed up sorting in postgres

I am using postgres 9.4. The messages has the following schema: messages belongs to feed_id, and has posted_at, also messages can have a parent message (in case of replies). ...
2
votes
1answer
135 views

Sorting by two columns conditionally [closed]

Column a has category ids, column b has set orders: +-------------+-----------+ | category_id | set_order | +-------------+-----------+ | 80 | null | | 81 | null | | ...
2
votes
1answer
982 views

Sort Warnings, finding out the query behind them

I'm troubleshooting a SQL Server 2012 that has started timing out as of a few weeks ago. The server is filled with thousands of sort warnings, at a rate of about 15 warnings per minute. To get the ...
2
votes
1answer
2k views

MySQL pivot query trouble sorting column by total

I am trying to return results for a matrix that represents the net weight that a country imports from another country. I have managed to write a query that produces a pivot type table in mysql all ...
2
votes
2answers
184 views

DB2 sorting by lowercase uppercase - problem

I'm struggling with DB2 - sorting by Polish letters with diacritics and uppercase/lowercase. When I created a database using: CREATE DATABASE P1DS8 AUTOMATIC STORAGE YES ON '/home/db2inst1' DBPATH ...
2
votes
1answer
776 views

MySQL : Avoid Temporary/Filesort Caused by GROUP BY Clause in Views

I'm planning on creating a view using this SQL SELECT, but the explain for it shows it's using temporary and using filesort. I can't figure out what indices I need in order to fix this problem. Mostly,...
2
votes
1answer
403 views

sorting groups of related rows by average values while keeping the groups together

I'm using PostgreSQL 8.4, but would like a standard SQL solution if possible. Consider the following table. corrmodel=# SELECT * from data limit 1; id | datasubgroup_id | datafile_id | ...
2
votes
0answers
15 views

How does the use of derived tables speed up sorting?

In the article 45 Ways To Speed Up Firebird Database, it states that Use derived tables to optimize SELECT with ORDER BY/GROUP BY Another way to optimize SQL query with sorting is to ...
2
votes
1answer
52 views

SQL Merge Statement Spending Large Amount of Time Sorting on Primary Key

We are looking to use the SQL MERGE statement in SQL Server 2012 to handle data replication for a data warehouse that we have access to from the manufacturer of a 3rd party application we use for data ...
2
votes
0answers
127 views

Schema for user drag and drop ordering

I'm trying to work out the schema for a system where users will be able to order items in an (unlimited length) list by drag and drop. Is there any kind of standard way of storing this ordering ...
1
vote
2answers
3k views

Estimated Execution Plan SQL Server Sort?

I'm running a query and its taking a age to execute, looking at the execution plan I can see that 51% of the cost is in the SORT? when in the actual query i am not ORDERING BY anything. Anyone got ...
1
vote
1answer
231 views

How to sort rows to appear alternating (e.g. A B A B … )?

Suppose I have a column x with values A and B. For example: Row X 1 A 2 A 3 A 4 B 5 B 6 B Now, I want to sort them into this fashion: Row X 1 A 2 B 3 A 4 B 5 A 6 B Of ...
1
vote
3answers
2k views

MySQL InnoDB Sorting Issue

I was surprised to see MySQL's InnoDB showing an interesting behavior, which I cannot fully explain. According to the official MySQL InnoDB Documentation: "All indexes other than the clustered ...
1
vote
1answer
71 views

Ordering in postgresql

I'm facing an issue whereas I do not understand. Running PostgreSQL on mac and have this query: select tldid, tldaction, to_char(tldactiondate, 'dd/mm/YYYY') as tldactiondate, ...
1
vote
1answer
164 views

Sorting a list of records alphabetically: is there any reason NOT to let the database do it

I have a list of records that contain a column of arbitrary strings. I would like the application to display them sorted in some order (preferably alphabetically, since humans have to read the data). ...
1
vote
2answers
3k views

Order by and then Concat

I have a table table1 like: col1 col2 A1 A2 A1 B1 A1 B2 A2 A1 A2 B1 A2 B2 B1 A1 B1 A2 B1 B2 B2 A1 B2 A2 B2 B1 I need to concat col1 and col2 such a way that it ...
1
vote
1answer
2k views

Sorting Result state taking very long time

I am using a MySQL 5.1.69-log DB for analysis purpose. I've designed my database in a star schema. All tables are using InnoDB. My innodb_buffer_pool_size=2Gb This is the query I am running : ...
1
vote
1answer
2k views

db INDEX on ORDER BY FIELD in very simple query does not help - still slow response?

I have very simple query which returns 200K records very slow (20 seconds). SELECT * FROM TABLE ORDER BY ID DESC If I do just SELECT * FROM TABLE it returns quick result. I created INDEX on ...
1
vote
1answer
855 views

ORDER BY on aggregate field on a closure table giving unexpected results

I am updating my companies product database and I'm looking into different ways to do design our faceted navigation "selector" tables. The idea of faceted navigation might look like this: It's ...
1
vote
1answer
2k views

Is it possible to add index to mysql with multiple column to optimize order by performance?

# I have a simple table create table t1 (c1 int, c2 int); # I want to do the following sorting select * from t1 order by c2 desc, c1 desc; select * from t1 order by c2 asc, c1 desc; # add ...
1
vote
1answer
231 views

Working of window functions and idea window size for window function

I am not able to understand the concept of window functions. How exactly they work and what are the pros and cons of such technique? I have read that using limit and offset is slow but its still used....
1
vote
1answer
31 views

Update all rows when sort/ordering value is changed for single row?

I am in the process of creating a GIS application with multiple layers and many pieces of content shapes on each layer. Currently each layer/shape is drawn in the order that it was returned from the ...
1
vote
1answer
136 views

SQL Server Query performance with window function

We write a query that include unpivot, partition by and order by.Query is: SELECT PersonId ,SalaryDate ,ID ,Type ,SalaryValue ,ROW_NUMBER() OVER ( PARTITION BY PersonId ...
1
vote
1answer
51 views

Keep one row per ID while keeping previous order (from ORDER BY)

I'm actually working on a big query and stuck at the very end. I'm working on MySQL 5.7. ID // SubID // Criteria 1 // Criteria 2 // ... // Critera n 1 // 2 // x // y // ... // ...
1
vote
2answers
84 views

High CPU usage from sorting result queries

I have two machine have two master-master mysql replicate, only problem i have that i got massive queries like "sorting result" queries and i don't know how to fix these queries . mysql process cpu ...
1
vote
0answers
79 views

HQL pagination returns same result on different pages - with SQL

We have the following query in the server (using sql): Query query = this.entityManager.createQuery( "SELECT type, id, date, amount FROM Transaction ORDER BY type ASC"); The type field ...