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  • Determine if an Index has been used as a hint

    - by Joe Bloggs
    In SQL Server, there is the option to use query hints. eg SELECT c.ContactID FROM Person.Contact c WITH (INDEX(AK_Contact_rowguid)) I am in the process of getting rid of unused indexes and was wondering how I could go about determining if an index was used as a query hint. Does anyone have suggestions on how I could do this? Cheers, Joe

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  • How to optimize this SQL query for a rectangular region?

    - by Andrew B.
    I'm trying to optimize the following query, but it's not clear to me what index or indexes would be best. I'm storing tiles in a two-dimensional plane and querying for rectangular regions of that plane. The table has, for the purposes of this question, the following columns: id: a primary key integer world_id: an integer foreign key which acts as a namespace for a subset of tiles tileY: the Y-coordinate integer tileX: the X-coordinate integer value: the contents of this tile, a varchar if it matters. I have the following indexes: "ywot_tile_pkey" PRIMARY KEY, btree (id) "ywot_tile_world_id_key" UNIQUE, btree (world_id, "tileY", "tileX") "ywot_tile_world_id" btree (world_id) And this is the query I'm trying to optimize: ywot=> EXPLAIN ANALYZE SELECT * FROM "ywot_tile" WHERE ("world_id" = 27685 AND "tileY" <= 6 AND "tileX" <= 9 AND "tileX" >= -2 AND "tileY" >= -1 ); QUERY PLAN ------------------------------------------------------------------------------------------------------------------------------------------- Bitmap Heap Scan on ywot_tile (cost=11384.13..149421.27 rows=65989 width=168) (actual time=79.646..80.075 rows=96 loops=1) Recheck Cond: ((world_id = 27685) AND ("tileY" <= 6) AND ("tileY" >= (-1)) AND ("tileX" <= 9) AND ("tileX" >= (-2))) -> Bitmap Index Scan on ywot_tile_world_id_key (cost=0.00..11367.63 rows=65989 width=0) (actual time=79.615..79.615 rows=125 loops=1) Index Cond: ((world_id = 27685) AND ("tileY" <= 6) AND ("tileY" >= (-1)) AND ("tileX" <= 9) AND ("tileX" >= (-2))) Total runtime: 80.194 ms So the world is fixed, and we are querying for a rectangular region of tiles. Some more information that might be relevant: All the tiles for a queried region may or may not be present The height and width of a queried rectangle are typically about 10x10-20x20 For any given (world, X) or (world, Y) pair, there may be an unbounded number of matching tiles, but the worst case is currently around 10,000, and typically there are far fewer. New tiles are created far less frequently than existing ones are updated (changing the 'value'), and that itself is far less frequent that just reading as in the query above. The only thing I can think of would be to index on (world, X) and (world, Y). My guess is that the database would be able to take those two sets and intersect them. The problem is that there is a potentially unbounded number of matches for either for either of those. Is there some other kind of index that would be more appropriate?

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  • mysql - speedup regex

    - by Uwe
    I have a table: +--------+------------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +--------+------------------+------+-----+---------+----------------+ | idurl | int(11) | NO | PRI | NULL | auto_increment | | idsite | int(10) unsigned | NO | MUL | NULL | | | url | varchar(2048) | NO | | NULL | | +--------+------------------+------+-----+---------+----------------+ the select statement is: SELECT idurl, url FROM URL WHERE idsite = 34 AND url REGEXP '^https\\://www\\.domain\\.com/checkout/step_one\\.php.*' The query needs 5 seconds on a table with 1000000 rows. Can I achieve a speedup with indexes or something else?

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  • Getting a specific bit value in a byte string

    - by ignoramus
    There is a byte at a specific index in a byte string which represents eight flags; one flag per bit in the byte. If a flag is set, its corresponding bit is 1, otherwise its 0. For example, if I've got b'\x21' the flags would be 0001 0101 # Three flags are set at indexes 3, 5 and 7 # and the others are not set What would be the best way to get each bit value in that byte, so I know whether a particular flag is set or not? (Preferably using bitwise operations)

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  • Oracle Stored Procedure with Alter command

    - by Will
    Hello, I am trying to build an oracle stored procedure which will accept a table name as a parameter. The procedure will then rebuild all indexes on the table. My problem is I get an error while using the ALTER command from a stored procedure, as if PLSQL does not allow that command.

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  • How to do run length encoding?

    - by Phoenix
    I have a long string for example it could be "aaaaaabbccc". Need to represent it as "a6b2c3". What's the best way to do this ? I could do this in linear time by comparing characters and incrementing counts and then replacing the counts in the array, using two indexes in one pass. Can you guys think of a better way than this? Are any of the encoding techniques going to work here ?

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  • How does the hash part in hash maps work?

    - by sub
    So there is this nice picture in the hash maps article on Wikipedia: Everything clear so far, except for the hash function in the middle. How can a function generate the right index from any string? Are the indexes integers in reality too? If yes, how can the function output 1 for John Smith, 2 for Lisa Smith, etc.?

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  • Does clustered index on foreign key column increase join performance vs non-clustered ?

    - by alpav
    In many places it's recommended that clustered indexes are better utilized when used to select range of rows using BETWEEN statement. When I select joining by foreign key field in such a way that this clustered index is used, I guess, that clusterization should help too because range of rows is being selected even though they all have same clustered key value and BETWEEN is not used. Considering that I care only about that one select with join and nothing else, am I wrong with my guess ?

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  • SQL Server 2008 Optimization

    - by hgulyan
    I've learned today, if you append to your query OPTION (MAXDOP 0) your query will run on multiple processors and if it's huge query, query will perform faster. I know general guidelines on query optimizations (using indexes, selecting only needed fields etc.), my question is about SQL Server optimization. Maybe changing some options in configurations or anything else. What guidelines are there for SQL Server Optimization? Thank you.

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  • Compact matlab matrix indexing notation

    - by AnnaR
    I've got an nxk sized matrix, containing k numbers per row. I want to use these k number as indexes to k-dimensional matrix. Is there any compact way of doing so in matlab or must I use a for-loop? This is what I want to do (in matlab-pseudo code), but in a more matlabish way. for row=1:1:n finalTable(row) = kDimensionalMatrix(indexmatrix(row, 1),... indexmatrix(row, 2),...,indexmatrix(row, k)) end

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  • MySQL forgot about automatically creating an index for a foreign key?

    - by bobo
    After running the following SQL statements, you will see that, MySQL has automatically created the non-unique index question_tag_tag_id_tag_id on the tag_id column for me after the first ALTER TABLE statement has run. But after the second ALTER TABLE statement has run, I think MySQL should also automatically create another non-unique index question_tag_question_id_question_id on the question_id column for me. But as you can see from the SHOW INDEXES statement output, it's not there. Why does MySQL forget about the second ALTER TABLE statement? By the way, since I have already created a unique index question_id_tag_id_idx used by both question_id and tag_id columns. Is creating a separate index for each of them redundant? mysql> DROP DATABASE mydatabase; Query OK, 1 row affected (0.00 sec) mysql> CREATE DATABASE mydatabase; Query OK, 1 row affected (0.00 sec) mysql> USE mydatabase; Database changed mysql> CREATE TABLE question (id BIGINT AUTO_INCREMENT, html TEXT, PRIMARY KEY(id)) ENGINE = INNODB; Query OK, 0 rows affected (0.05 sec) mysql> CREATE TABLE tag (id BIGINT AUTO_INCREMENT, name VARCHAR(10) NOT NULL, UNIQUE INDEX name_idx (name), PRIMARY KEY(id)) ENGINE = INNODB; Query OK, 0 rows affected (0.05 sec) mysql> CREATE TABLE question_tag (question_id BIGINT, tag_id BIGINT, UNIQUE INDEX question_id_tag_id_idx (question_id, tag_id), PRIMARY KEY(question_id, tag_id)) ENGINE = INNODB; Query OK, 0 rows affected (0.00 sec) mysql> ALTER TABLE question_tag ADD CONSTRAINT question_tag_tag_id_tag_id FOREIGN KEY (tag_id) REFERENCES tag(id); Query OK, 0 rows affected (0.10 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> ALTER TABLE question_tag ADD CONSTRAINT question_tag_question_id_question_id FOREIGN KEY (question_id) REFERENCES question(id); Query OK, 0 rows affected (0.13 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> SHOW INDEXES FROM question_tag; +--------------+------------+----------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | +--------------+------------+----------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | question_tag | 0 | PRIMARY | 1 | question_id | A | 0 | NULL | NULL | | BTREE | | | question_tag | 0 | PRIMARY | 2 | tag_id | A | 0 | NULL | NULL | | BTREE | | | question_tag | 0 | question_id_tag_id_idx | 1 | question_id | A | 0 | NULL | NULL | | BTREE | | | question_tag | 0 | question_id_tag_id_idx | 2 | tag_id | A | 0 | NULL | NULL | | BTREE | | | question_tag | 1 | question_tag_tag_id_tag_id | 1 | tag_id | A | 0 | NULL | NULL | | BTREE | | +--------------+------------+----------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 5 rows in set (0.01 sec) mysql>

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  • SQL Server unique constraint problem

    - by b0x0rz
    How to create a unique constraint on a varchar(max) field in visual studio, visually. the problem is when i try it: manage indexes and keys add columns I can only chose the bigint columns, but not any of the varchar(max) ones. Do I maybe have to use check constraints? If yes, what to put in the expression? Thnx for the info

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  • Configure mod_jk with mod_rewrite

    - by Ayyappan
    Dear all Is there any way to configure both mod_jk and .htaccess in a same call what are the steps follow plz replay me httpd.conf ServerAdmin "[email protected]" ServerName www.vpaycash.in MIMEMagicFile /dev/null CustomLog logs/vpaycash.in_access_log "%h %l %u %t \"%r\" %s %b\"%{Referer}i\" \"%{User-agent}i\"" ErrorLog logs/vpaycash.in_error_log DocumentRoot "/home/vpaycashinadmin/webapps" Options +Indexes +FollowSymLinks Order allow,deny Allow from all AllowOverride All JkMount /* wlb JkMount /*.faces wlb JkMount /*.html wlb JkMount /*.iface wlb JkMount /*.jspx wlb JkMount /TestFilter wlb JkMount /block/* wlb JkMount /xmlhttp/* wlb Alias /usage "/home/vpaycashinadmin/public_html/usage" Order allow,deny Allow from all .htacess RewriteEngine on RewriteRule ^index.html$ index.iface

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  • Does the order of columns in a query matter?

    - by James Simpson
    When selecting columns from a MySQL table, is performance affected by the order that you select the columns as compared to their order in the table (not considering indexes that may cover the columns)? For example, you have a table with rows uid, name, bday, and you have the following query. SELECT uid, name, bday FROM table Does MySQL see the following query any differently and thus cause any sort of performance hit? SELECT uid, bday, name FROM table

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  • SQL Server unique contraint problem

    - by b0x0rz
    How to create a unique constraint on a varchar(max) field in visual studio, visually. the problem is when i try it: manage indexes and keys add columns i can only chose the bigint columns, but not any of the varchar(max) ones. do i maybe have to use check constraints? if yes, what to put in the expression? thnx for the info

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  • Why is my List.Sort method in C# reversing the order of my list?

    - by Fiona Holder
    I have a list of items in a generic list: A1 (sort index 1) A2 (sort index 2) B1 (sort index 3) B2 (sort index 3) B3 (sort index 3) The comparator on them takes the form: this.sortIndex.CompareTo(other.sortIndex) When I do a List.Sort() on the list of items, I get the following order out: A1 A2 B3 B2 B1 It has obviously worked in the sense that the sort indexes are in the right order, but I really don't want it to be re-ordering the 'B' items. Is there any tweak I can make to my comparator to fix this?

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  • SQLite If Column Exists

    - by Nathan
    I was wondering if there is a nice IF NOT EXISTS for checking columns and indexes in SQLite, or do I need to bring back the entire database schema and validate against that?

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  • Grails' GORM constraint question

    - by xain
    Hi, I have the following Domain Class: class Metric { String name float value static belongsTo = [Person,Corporation] static indexes = { name() } } How can I add a constraint so Person,Corporation and name are unique ? Thanks.

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  • mysql insert and buffers, is this possible

    - by Grumpy
    how is this possible first i do insert into table2 select * from table1 where table1.id=1 ( 50k records should be moved 6 indexes has to be updated ) second delete from table1 where id=1 ( 50k records are removed ) How is it possible that only 45k of records are moved? Im scratching my head over this and cant find a right answer Is it possible that the insert is still active and delete already started

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