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  • In SQL, in what situation do we want to Index a field in a table, or 2 fields in a table at the same

    - by Jian Lin
    In SQL, it is obvious that whenever we want to do a search on millions of record, say CustomerID in a Transactios table, then we want to add an index for CustomerID. Is another situation we want to add an index to a field when we need to do inner join or outer join using that field as a criteria? Such as Inner join on t1.custumerID = t2.customerID. Then if we don't have an index on customerID on both tables, we are looking at O(n^2) because we need to loop through the 2 tables sequentially. If we have index on customerID on both tables, then it becomes O( (log n) ^ 2 ) and it is much faster. Any other situation where we want to add an index to a field in a table? What about adding index for 2 fields combined in a table. That is, one index, for 2 fields together?

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  • Tell me SQL Server Full-Text searcher is crazy, not me.

    - by Ian Boyd
    i have some customers with a particular address that the user is searching for: 123 generic way There are 5 rows in the database that match: ResidentialAddress1 ============================= 123 GENERIC WAY 123 GENERIC WAY 123 GENERIC WAY 123 GENERIC WAY 123 GENERIC WAY i run a FT query to look for these rows. i'll show you each step as i add more criteria to the search: SELECT ResidentialAddress1 FROM Patrons WHERE CONTAINS(Patrons.ResidentialAddress1, '"123*"') ResidentialAddress1 ========================= 123 MAPLE STREET 12345 TEST 123 MINE STREET 123 GENERIC WAY 123 FAKE STREET ... (30 row(s) affected) Okay, so far so good, now adding the word "generic": SELECT ResidentialAddress1 FROM Patrons WHERE CONTAINS(Patrons.ResidentialAddress1, '"123*"') AND CONTAINS(Patrons.ResidentialAddress1, '"generic*"') ResidentialAddress1 ============================= 123 GENERIC WAY 123 GENERIC WAY 123 GENERIC WAY 123 GENERIC WAY 123 GENERIC WAY (5 row(s) affected) Excellent. And now i'l add the final keyword that the user wants to make sure exists: SELECT ResidentialAddress1 FROM Patrons WHERE CONTAINS(Patrons.ResidentialAddress1, '"123*"') AND CONTAINS(Patrons.ResidentialAddress1, '"generic*"') AND CONTAINS(Patrons.ResidentialAddress1, '"way*"') ResidentialAddress1 ------------------------------ (0 row(s) affected) Huh? No rows? What if i query for just "way*": SELECT ResidentialAddress1 FROM Patrons WHERE CONTAINS(Patrons.ResidentialAddress1, '"way*"') ResidentialAddress1 ------------------------------ (0 row(s) affected) At first i thought that perhaps it's because of the *, and it's requiring that the root way have more characters after it. But that's not true: Searching for "123*" matches "123" Searching for "generic*" matches "generic" Books online says, The asterisk matches zero, one, or more characters What if i remove the * just for s&g: SELECT ResidentialAddress1 FROM Patrons WHERE CONTAINS(Patrons.ResidentialAddress1, '"way"') Server: Msg 7619, Level 16, State 1, Line 1 A clause of the query contained only ignored words. So one might think that you are just not allowed to even search for way, either alone, or as a root. But this isn't true either: SELECT * FROM Patrons WHERE CONTAINS(Patrons.*, '"way*"') AccountNumber FirstName Lastname ------------- --------- -------- 33589 JOHN WAYNE So sum up, the user is searching for rows that contain all the words: 123 generic way Which i, correctly, translate into the WHERE clauses: SELECT * FROM Patrons WHERE CONTAINS(Patrons.*, '"123*"') AND CONTAINS(Patrons.*, '"generic*"') AND CONTAINS(Patrons.*, '"way*"') which returns no rows. Tell me this just isn't going to work, that it's not my fault, and SQL Server is crazy. Note: i've emptied the FT index and rebuilt it.

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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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  • List of all index & index columns in SQL Server DB

    - by Anton Gogolev
    How do I get a list of all index & index columns in SQL Server 2005+? The closest I could get is: select s.name, t.name, i.name, c.name from sys.tables t inner join sys.schemas s on t.schema_id = s.schema_id inner join sys.indexes i on i.object_id = t.object_id inner join sys.index_columns ic on ic.object_id = t.object_id inner join sys.columns c on c.object_id = t.object_id and ic.column_id = c.column_id where i.index_id > 0 and i.type in (1, 2) -- clustered & nonclustered only and i.is_primary_key = 0 -- do not include PK indexes and i.is_unique_constraint = 0 -- do not include UQ and i.is_disabled = 0 and i.is_hypothetical = 0 and ic.key_ordinal > 0 order by ic.key_ordinal which is not exactly what I want. What I want is to list all user-defined indexes (which means no indexes which support unique constraints & primary keys) with all columns (ordered by how do they apper in index definition) plus as much metadata as possible.

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  • Lucene.NET - Find documents that do not contain a specified field

    - by Brandon
    Let's say I have 2 instance of a class called 'Animal'. Animal has 3 fields: Name, Age, and Type The name field is nullable, so before I insert an instance of Animal as a Lucene indexed document, I check if Animal.Name == null, and if it does, I do not insert it as a field in my document. If I were to retrieve all animals, I would see that the Name field does not exist and I can set its value to null. However, there may be situations where I want to say "Get me all animals that do not have a name specified yet." In this situation I want to retrieve all Lucene.NET documents from my animal index that do not contain the Name field. Is there an easy way to do this with Lucene.NET? I want to stay away from having to perform some sort of hack to check if my name field has a value of 'null'.

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  • SQL SERVER - Detecting non-indexed columns but used in WHERE clause

    - by Vadi
    How to detect a column included in WHERE clause but used in indexed? Little Background: Until the time the table has few number of records things will be okay, once it started having millions of records then index should be created for a column which is used in WHERE clauses in stored procs, inline queries etc., Since we have hundreds of stored procs and queries that often gets changed by the devs I wanted to have a automated way of identifying those columns that are used in WHERE clauses but not an index is created. How to do that in SQL SERVER 2008?

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  • Multi-variable indexes in postgres

    - by Jackson Davis
    Im looking at an application where I will be doing quite a few SELECTs where I am trying to find column_a = x AND column_b = y. Is the correct to create that index that something like the following? CREATE INDEX index_name ON table (column_a, column_b)

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  • jQuery - Finding the element index relative to its container

    - by Hary
    Here's my HTMl structure: <div id="main"> <div id="inner-1"> <img /> <img /> <img /> </div> <div id="inner-2"> <img /> <img class="selected" /> <img /> </div> <div id="inner-3"> <img /> <img /> <img /> </div> </div> What I'm trying to do is get the index of the img.selected element relative to the #main div. So in this example, the index should be 4 (assuming 0 based index) and not 1. My usual way to go about getting indexes is using $element.prevAll().length but, obviously, that will return the index relative to the #inner-2 div. I've tried using $('img.selected').prevAll('#main').length but that's returning 0 :/

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  • How to index a date column with null values?

    - by Heinz Z.
    How should I index a date column when some rows has null values? We have to select rows between a date range and rows with null dates. We use Oracle 9.2 and higher. Options I found Using a bitmap index on the date column Using an index on date column and an index on a state field which value is 1 when the date is null Using an index on date column and an other granted not null column My thoughts to the options are: to 1: the table have to many different values to use an bitmap index to 2: I have to add an field only for this purpose and to change the query when I want to retrieve the null date rows to 3: locks tricky to add an field to an index which is not really needed What is the best practice for this case? Thanks in advance Some infos I have read: Oracle Date Index When does Oracle index null column values?

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  • Creating an appropriate index for a frequently used query in SQL Server

    - by Slauma
    In my application I have two queries which will be quite frequently used. The Where clauses of these queries are the following: WHERE FieldA = @P1 AND (FieldB = @P2 OR FieldC = @P2) and WHERE FieldA = @P1 AND FieldB = @P2 P1 and P2 are parameters entered in the UI or coming from external datasources. FieldA is an int and highly on-unique, means: only two, three, four different values in a table with say 20000 rows FieldB is a varchar(20) and is "almost" unique, there will be only very few rows where FieldB might have the same value FieldC is a varchar(15) and also highly distinct, but not as much as FieldB FieldA and FieldB together are unique (but do not form my primary key, which is a simple auto-incrementing identity column with a clustered index) I'm wondering now what's the best way to define an index to speed up specifically these two queries. Shall I define one index with... FieldB (or better FieldC here?) FieldC (or better FieldB here?) FieldA ... or better two indices: FieldB FieldA and FieldC FieldA Or are there even other and better options? What's the best way and why? Thank you for suggestions in advance!

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  • compare two following values in numpy array

    - by Billy Mitchell
    What is the best way to touch two following values in an numpy array? example: npdata = np.array([13,15,20,25]) for i in range( len(npdata) ): print npdata[i] - npdata[i+1] this looks really messed up and additionally needs exception code for the last iteration of the loop. any ideas? Thanks!

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  • Full-text search in C++

    - by Jen
    I have a database of many (though relatively short) HTML documents. I want users to be able to search this database by entering one or more search words in a C++ desktop application. Hence, I’m looking for a fast full-text search solution. Ideally, it should: Skip common words, such as the, of, and, etc. Support stemming, i.e. search for run also finds documents containing runner, running and ran. Be able to update its index in the background as new documents are added to the database. Be able to provide search word suggestions (like Google Suggest) To illustrate, assume the database has just two documents: Document 1: This is a test of text search. Document 2: Testing is fun. The following words should be in the index: fun, search, test, testing, text. If the user types t in the search box, I want the application to be able to suggest test, testing and text (Ideally, the application should be able to query the search engine for the 10 most common search words starting with t). A search for testing should return both documents. Can you suggest a C or C++ based solution? (I’ve briefly reviewed CLucene and Xapian, but I’m not sure if either will address my needs, especially querying the search word indexes for the suggest feature).

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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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  • A question about indexes regarding to the gain of inserts & updates in database

    - by Mestika
    Hi, I’m having a question about the fine line between the gain of an index to a table there is growing steadily in size every month and the gain of queries with an index. The situation is, that I’ve two tables, Table1 and Table2. Each table grows slowly but regularly each month (with about 100 new rows for Table1 and a couple of rows for Table2). My concrete question is whether to have an index or to drop it. I’ve made some measurement that an covering index on Table2 improve my SELECT queries and some rather much but again, I’ve to consider the pros and cons but having a really hard time to decide. For Table1 it might not be necessary to have an index because the SELECT queries there is not that common. I would appreciate any suggestion, tips or just good advice to what is a good solution. By the way, I’m using IBM DB2 version 9.7 as my Database system Sincerely Mestika

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  • iphone indexed table view problem

    - by steveY
    I have a table view in which I'm using sectionIndexTitlesForTableView to display an index. However, when I scroll the table, the index scrolls with it. This also results in very slow refreshing of the table. Is there something obvious I could be doing wrong? I want the index to remain in place on the right while the table scrolls. This is the code I'm using for the index titles: - (NSArray *)sectionIndexTitlesForTableView:(UITableView *)tableView { NSMutableArray *tempArray = [[NSMutableArray alloc] init]; [tempArray addObject:@"A"]; [tempArray addObject:@"B"]; [tempArray addObject:@"C"]; [tempArray addObject:@"D"]; ... return tempArray; }

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  • Lucene Analyzer to Use With Special Characters and Punctuation?

    - by Brandon
    I have a Lucene index that has several documents in it. Each document has multiple fields such as: Id Project Name Description The Id field will be a unique identifier such as a GUID, Project is a user's ProjectID and a user can only view documents for their project, and Name and Description contain text that can have special characters. When a user performs a search on the Name field, I want to be able to attempt to match the best I can such as: First Will return both: First.Last and First.Middle.Last Name can also be something like: Test (NameTest) Where, if a user types in 'Test', 'Name', or '(NameTest)', then they can find the result. However, if I say that Project is 'ProjectA' then that needs to be an exact match (case insensitive search). The same goes with the Id field. Which fields should I set up as Tokenized and which as Untokenized? Also, is there a good Analyzer I should consider to make this happen? I am stuck trying to decide the best route to implement the desired searching.

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  • Approach for altering Primary Key from GUID to BigInt in SQL Server related tables

    - by Tom
    I have two tables with 10-20 million rows that have GUID primary keys and at leat 12 tables related via foreign key. The base tables have 10-20 indexes each. We are moving from GUID to BigInt primary keys. I'm wondering if anyone has any suggestions on an approach. Right now this is the approach I'm pondering: Drop all indexes and fkeys on all the tables involved. Add 'NewPrimaryKey' column to each table Make the key identity on the two base tables Script the data change "update table x, set NewPrimaryKey = y where OldPrimaryKey = z Rename the original primarykey to 'oldprimarykey' Rename the 'NewPrimaryKey' column 'PrimaryKey' Script back all the indexes and fkeys Does this seem like a good approach? Does anyone know of a tool or script that would help with this? TD: Edited per additional information. See this blog post that addresses an approach when the GUID is the Primary: http://www.sqlmag.com/blogs/sql-server-questions-answered/sql-server-questions-answered/tabid/1977/entryid/12749/Default.aspx

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  • Database indexes and their Big-O notation

    - by miket2e
    I'm trying to understand the performance of database indexes in terms of Big-O notation. Without knowing much about it, I would guess that: Querying on a primary key or unique index will give you a O(1) lookup time. Querying on a non-unique index will also give a O(1) time, albeit maybe the '1' is slower than for the unique index (?) Querying on a column without an index will give a O(N) lookup time (full table scan). Is this generally correct ? Will querying on a primary key ever give worse performance than O(1) ? My specific concern is for SQLite, but I'd be interested in knowing to what extent this varies between different databases too.

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  • Keeping DB Table sorted using multi-field formula (Microsoft SQL Server)

    - by user298167
    I have a JOB table, with two interesting columns: Creation Date Importance (high - 3, medium 2, low - 1). A JOB record's priority calculated like this: Priority = Importance * (time passed since creation) The problem is, every time I would like to pick 200 jobs with highest priority, and I don't want to resort the table. Is there a way to keep rows sorted? I was also thinking about having three tables one for High, Medium and Low and then sort those by Creation Date.

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  • Fulltext and composite indexes and how they affect the query

    - by Brett
    Just say I had a query as below.. SELECT name,category,address,city,state FROM table WHERE MATCH(name,subcategory,category,tag1) AGAINST('education') AND city='Oakland' AND state='CA' LIMIT 0, 10; ..and I had a fulltext index as name,subcategory,category,tag1 and a composite index as city,state; is this good enough for this query? Just wondering if something extra is needed when mixing additional AND's when making use of the fulltext index with the MATCH/AGAINST. Edit: What I am trying to understand is, what happens with the additional columns that are within the query but are not indexed in the chosen index (the fulltext index), the above example being city and state. How does MySQL now find the matching rows for these since it can't use two indexes (or can it?) - so, basically, I'm trying to understand how MySQL goes about finding the data optimally for the columns NOT in the chosen fulltext index and if there is anything I can or should do to optimize the query.

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  • mysql query and index

    - by parm.95
    Does this query will be faster with a index on "t.type1" and "x.type1" or only index on "x.type1" is enought? SELECT t.id, x.id FROM t INNER JOIN x ON x.type1=t.type1 WHERE t.id=1

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  • How to get Google Search Query Kind of Content Indexed ?

    - by Sunil
    Hello: I was looking for something like flash grabber and I came across this result http://www.giveawayoftheday.com/flash+grabber+firefox/ I am just wondering how giveawayoftheday has managed to get "flash+grabber+firefox/" indexed in Google ? Did they submit via Google Sitemap or is Google doing this on its own ? Or something else ? Kindly enlighten. Thanks.

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