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• postgresql: Fast way to update the latest inserted row

  - by Anonymous

  What is the best way to modify the latest added row without using a temporary table. E.g. the table structure is id | text | date My current approach would be an insert with the postgresql specific command "returning id" so that I can update the table afterwards with update myTable set date='2013-11-11' where id = lastRow However I have the feeling that postgresql is not simply using the last row but is iterating through millions of entries until "id = lastRow" is found. How can i directly access the last added row?

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• To log in stored procedures?

  - by hgulyan

  If you have a long running SP, do you log somehow it's actions or just wait for this message? "Command(s) completed successfully." I assume, that there can be plenty solutions on this subject, but is there any best practice - a simple solution that is frequently used?

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• Why would I do an inner join on a non-distinct field?

  - by froadie

  I just came across a query that does an inner join on a non-distinct field. I've never seen this before and I'm a little confused about this usage. Something like: SELECT distinct all, my, stuff FROM myTable INNER JOIN myOtherTable ON myTable.nonDistinctField = myOtherTable.nonDistinctField (WHERE some filters here...) I'm not quite sure what my question is or how to phrase it, or why exactly this confuses me, but I was wondering if anyone could explain why someone would need to do an inner join on a non-distinct field and then select only distinct values...? Is there ever a legitimate use of an inner join on a non-distinct field? What would be the purpose? And if there's is a legitimate reason for such a query, can you give examples of where it would be used?

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• Query to find all the nodes that are two steps away from a particular node.

  - by iecut

  Suppose I have two columns in a table that represents a graph, the first column is a FROMNODE and second one is TONODE. What I would like to know is that how will we find all the nodes that are two steps away from a particular node. Lets suppose I have a node numbered '1' and i would like to know all the nodes that are two steps away from it. I have tried(I am assuming the table name as graph) SELECT FROMNODE FROM GRAPH WHERE TONODE=1 (this is to select all the nodes that are connected to node 1, but I couldn't figure out how would I find all the nodes that are two steps away from node 1??)

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• How to calculate the sum of a column in an MS Access table for a given date (a single day, month or year)

  - by cMinor

  I have a table in Access in a custom format saved as dd/MM/yyyy hh:mm:ss tt , Also A form in VB.NET 2010, I get a specific day, month and year with no problem but the problem comes when I want to query the sum of a column named value depending on a specific month or day or year.... The table is like: +-----+-----------+-------------------------+ | id | value | date | +-----+-----------+-------------------------+ | id1 | 1499 | 01/01/2012 07:30:11 p.m.| | id2 | 1509 | 11/02/2012 07:30:11 p.m.| | id3 | 1611 | 21/10/2012 07:30:11 p.m.| | id1 | 1115 | 11/10/2012 07:30:11 p.m.| | id1 | 1499 | 17/05/2012 07:30:11 p.m.| | id2 | 1709 | 11/06/2012 07:30:11 p.m.| | id3 | 1911 | 30/07/2012 07:30:11 p.m.| | id1 | 1015 | 01/08/2012 07:30:11 p.m.| | id1 | 1000 | 11/05/2012 07:30:11 p.m.| |+-----+-----------+------------------------+ So I Know the query SELECT SUM(value) FROM mytable WHERE date in='01/05/2012 00:00:00' ... How to tell the query I want the month of May so I would get 1499+1000= 2499 Or how to tell I want the year 2012 so I would get the sum of all the table Which would be the correct syntax...

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• Strange: Planner takes decision with lower cost, but (very) query long runtime

  - by S38

  Facts: PGSQL 8.4.2, Linux I make use of table inheritance Each Table contains 3 million rows Indexes on joining columns are set Table statistics (analyze, vacuum analyze) are up-to-date Only used table is "node" with varios partitioned sub-tables Recursive query (pg = 8.4) Now here is the explained query: WITH RECURSIVE rows AS ( SELECT * FROM ( SELECT r.id, r.set, r.parent, r.masterid FROM d_storage.node_dataset r WHERE masterid = 3533933 ) q UNION ALL SELECT * FROM ( SELECT c.id, c.set, c.parent, r.masterid FROM rows r JOIN a_storage.node c ON c.parent = r.id ) q ) SELECT r.masterid, r.id AS nodeid FROM rows r QUERY PLAN ----------------------------------------------------------------------------------------------------------------------------------------------------------------- CTE Scan on rows r (cost=2742105.92..2862119.94 rows=6000701 width=16) (actual time=0.033..172111.204 rows=4 loops=1) CTE rows -> Recursive Union (cost=0.00..2742105.92 rows=6000701 width=28) (actual time=0.029..172111.183 rows=4 loops=1) -> Index Scan using node_dataset_masterid on node_dataset r (cost=0.00..8.60 rows=1 width=28) (actual time=0.025..0.027 rows=1 loops=1) Index Cond: (masterid = 3533933) -> Hash Join (cost=0.33..262208.33 rows=600070 width=28) (actual time=40628.371..57370.361 rows=1 loops=3) Hash Cond: (c.parent = r.id) -> Append (cost=0.00..211202.04 rows=12001404 width=20) (actual time=0.011..46365.669 rows=12000004 loops=3) -> Seq Scan on node c (cost=0.00..24.00 rows=1400 width=20) (actual time=0.002..0.002 rows=0 loops=3) -> Seq Scan on node_dataset c (cost=0.00..55001.01 rows=3000001 width=20) (actual time=0.007..3426.593 rows=3000001 loops=3) -> Seq Scan on node_stammdaten c (cost=0.00..52059.01 rows=3000001 width=20) (actual time=0.008..9049.189 rows=3000001 loops=3) -> Seq Scan on node_stammdaten_adresse c (cost=0.00..52059.01 rows=3000001 width=20) (actual time=3.455..8381.725 rows=3000001 loops=3) -> Seq Scan on node_testdaten c (cost=0.00..52059.01 rows=3000001 width=20) (actual time=1.810..5259.178 rows=3000001 loops=3) -> Hash (cost=0.20..0.20 rows=10 width=16) (actual time=0.010..0.010 rows=1 loops=3) -> WorkTable Scan on rows r (cost=0.00..0.20 rows=10 width=16) (actual time=0.002..0.004 rows=1 loops=3) Total runtime: 172111.371 ms (16 rows) (END) So far so bad, the planner decides to choose hash joins (good) but no indexes (bad). Now after doing the following: SET enable_hashjoins TO false; The explained query looks like that: QUERY PLAN ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- CTE Scan on rows r (cost=15198247.00..15318261.02 rows=6000701 width=16) (actual time=0.038..49.221 rows=4 loops=1) CTE rows -> Recursive Union (cost=0.00..15198247.00 rows=6000701 width=28) (actual time=0.032..49.201 rows=4 loops=1) -> Index Scan using node_dataset_masterid on node_dataset r (cost=0.00..8.60 rows=1 width=28) (actual time=0.028..0.031 rows=1 loops=1) Index Cond: (masterid = 3533933) -> Nested Loop (cost=0.00..1507822.44 rows=600070 width=28) (actual time=10.384..16.382 rows=1 loops=3) Join Filter: (r.id = c.parent) -> WorkTable Scan on rows r (cost=0.00..0.20 rows=10 width=16) (actual time=0.001..0.003 rows=1 loops=3) -> Append (cost=0.00..113264.67 rows=3001404 width=20) (actual time=8.546..12.268 rows=1 loops=4) -> Seq Scan on node c (cost=0.00..24.00 rows=1400 width=20) (actual time=0.001..0.001 rows=0 loops=4) -> Bitmap Heap Scan on node_dataset c (cost=58213.87..113214.88 rows=3000001 width=20) (actual time=1.906..1.906 rows=0 loops=4) Recheck Cond: (c.parent = r.id) -> Bitmap Index Scan on node_dataset_parent (cost=0.00..57463.87 rows=3000001 width=0) (actual time=1.903..1.903 rows=0 loops=4) Index Cond: (c.parent = r.id) -> Index Scan using node_stammdaten_parent on node_stammdaten c (cost=0.00..8.60 rows=1 width=20) (actual time=3.272..3.273 rows=0 loops=4) Index Cond: (c.parent = r.id) -> Index Scan using node_stammdaten_adresse_parent on node_stammdaten_adresse c (cost=0.00..8.60 rows=1 width=20) (actual time=4.333..4.333 rows=0 loops=4) Index Cond: (c.parent = r.id) -> Index Scan using node_testdaten_parent on node_testdaten c (cost=0.00..8.60 rows=1 width=20) (actual time=2.745..2.746 rows=0 loops=4) Index Cond: (c.parent = r.id) Total runtime: 49.349 ms (21 rows) (END) - incredibly faster, because indexes were used. Notice: Cost of the second query ist somewhat higher than for the first query. So the main question is: Why does the planner make the first decision, instead of the second? Also interesing: Via SET enable_seqscan TO false; i temp. disabled seq scans. Than the planner used indexes and hash joins, and the query still was slow. So the problem seems to be the hash join. Maybe someone can help in this confusing situation? thx, R.

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• Concatenating rows from different tables into one field

  - by Markus

  Hi! In a project using a MSSQL 2005 Database we are required to log all data manipulating actions in a logging table. One field in that table is supposed to contain the row before it was changed. We have a lot of tables so I was trying to write a stored procedure that would gather up all the fields in one row of a table that was given to it, concatenate them somehow and then write a new log entry with that information. I already tried using FOR XML PATH and it worked, but the client doesn't like the XML notation, they want a csv field. Here's what I had with FOR XML PATH: DECLARE @foo varchar(max); SET @foo = (SELECT * FROM table WHERE id = 5775 FOR XML PATH('')); The values for "table", "id" and the actual id (here: 5775) would later be passed in via the call to the stored procedure. Is there any way to do this without getting XML notation and without knowing in advance which fields are going to be returned by the SELECT statement?

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• MySQL slow query

  - by andrhamm

  SELECT items.item_id, items.category_id, items.title, items.description, items.quality, items.type, items.status, items.price, items.posted, items.modified, zip_code.state_prefix, zip_code.city, books.isbn13, books.isbn10, books.authors, books.publisher FROM ( ( items LEFT JOIN bookitems ON items.item_id = bookitems.item_id ) LEFT JOIN books ON books.isbn13 = bookitems.isbn13 ) LEFT JOIN zip_code ON zip_code.zip_code = items.item_zip WHERE items.rid = $rid` I am running this query to get the list of a user's items and their location. The zip_code table has over 40k records and this might be the issue. It currently takes up to 15 seconds to return a list of about 20 items! What can I do to make this query more efficient?

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• Do a query only if there are no results on previous query

  - by yes123

  Hi guys: I do this query(1): (1)SELECT * FROM t1 WHERE title LIKE 'key%' LIMIT 1 I need to do a second(2) query only if this previous query has no results (2)SELECT * FROM t1 WHERE title LIKE '%key%' LIMIT 1 basically i need only 1 row who got the most close title to my key. Atm i am using an UNION query with a custom field to order it and a LIMIT 1. Problem is I don't want to do the others query if already the first made the result. Thanks

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• How to switch from MSSQL to MySQL for using with Excel pivot

  - by Sim

  Hi all, I have a table that contains sales transaction (~20 mil rows). Previously I used MSSQL and export it to an Excel pivot. Data refresh took 10-15 minutes but still do-able. However, after I migrated to MySQL (using XamppLite & ODBC), it took forever to refresh the data in the Excel pivot. Maybe I didn't optimize the MySQL good enough ? Anyone can share some thoughts 'bout this ? Thanks

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• How do views reduce code duplication?

  - by Debuger

  Hi! I read something like this about db views: Views are incredibly powerful and useful for one reason that stands out above all the other very good reasons. They reduce code duplication. That is, in most cases, the bottom line. If a query will be used in three or more places, then a view will drastically simplify your changes if the schema or query parameters change. I once had to edit 22 stored procedures to change some query logic. If the original architecture had utilized views, then I would have had only three changes. Can anyone explain to me how it works, and maybe give me some examples? Best regards!

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• Check if stored proc exists in ADO.Net?

  - by HeavyWave

  How do I check that a stored procedure exists using ADO.Net? Is there a specific way to do this (apart from executing SELECT OBJECT_ID() and checking the result)?

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• Error: The conversion of a nvarchar data type to a datetime data type resulted in an out-of-range value

  - by CPM

  I know that there are simmilar questions like this on the forum, however I am still having problems to update a datetime field o the database. I dont get any problems when inserting but I get problems when updating and I am formating the same way , like this: e.Values.Item("SelectionStartDate") = Format(startdate, "yyyy-MM-dd") + " " + startTime1 + ".000" startTime is of type string. I have tried different solution that I came across on the internet but still get this error. Please help. Thanks in advance

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• Should I include user_id in multiple tables?

  - by Drarok

  I'm at the planning stages of a multi-user application where each user will only have access their own data. There'll be a few tables that relate to each other, so I could use JOINs to ensure they're accessing only their data, but should I include user_id in each table? Would this be faster? It would certainly make some of the queries easier in the long run. Thanks!

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• What resources will help me understand the fundamentals of Relational Database Systems.

  - by Rachel

  This are few of the fundamental database questions which has always given me trouble. I have tried using google and wiki but I somehow I miss out on understanding the functionality rather than terminology. If possible would really appreciate if someone can share more insights on this questions using some visual representative examples. What is a key? A candidate key? A primary key? An alternate key? A foreign key? What is an index and how does it help your database? What are the data types available and when to use which ones?

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• automatic id generation which is a primary key

  - by abhi

  in vb.net while entering a new entry i want to assign a record a unique id like in case of numeric i do this way Dim ItemID As Integer KAYAReqConn.Open() SQLCmd = New SqlCommand("SELECT ISNULL(MAX(ItemID),0) AS ItemID from MstItem", ReqConn) Dim dr As SqlDataReader dr = SQLCmd.ExecuteReader If dr.HasRows Then dr.Read() ItemID = dr("ItemID") + 1 End If dr.Close() in this case m using itemid as a unique id and the format is 1,2,3... and m finding out the max and assigning to a new record but how to assign if the previous id is of the a00001,a00002,a00003,a00004...so on. how i do i produce a unique id in this case

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• ASP.NET GridView Sort?

  - by Curtis White

  I'm performing a query with a sort in the Selecting event of the LinqDataSource. I'm then casting my query to a list and assigning it to the result. I'm using this data source in an ASP.NET gridview. I can see the list is sorted but when the ASP.NET gridview does not seem to be respecting the sort order. How can I get the gridview to respect my default sort order?

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• What is an example of relational data and what is an example of a document?

  - by Aaron Fischer

  I am looking for examples of when to use a relational data base vs when to use a document database.

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• archiving strategies and limitations of data in a table

  - by Samuel

  Environment: Jboss, Mysql, JPA, Hibernate Our web application will be catering to a large amount of users (~ 1,000,000) and there are a lots of child table where user specific data are stored (e.g. personal, health, forum contributions ...). What would be the best practice to archive user & user specific information. [a] Would it be wise to move the archived user & user specific information to their respective tables within the same database (e.g. user_archive, user_forum_comments_archive ...) OR [b] Would you just mark the database entries with a flag in the original table(s) and just query only non archived entries. We have a unique constraint on User.loginid, how do you handle this requirement if the users are archived via 1-[a] (i.e if a user with loginid 'samuel' gets moved into the archive table and if a new user gets added with the same name in the original table, how would you prevent this. What would be the best strategy to address the unique key constraints. We have a requirement to selectively archive records and bring it back if necessary, will you rely on database tools are would you handle this via your persistence APIs exposed by the JPA entity model.

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• Replacing characters with specified one

  - by mahesh

  Hello All, I have a string as follows - MFMFMF now i want to change this string to FMFMFM how to do this , help needed pls i had tried select replace(replace('mfmfmf','M','F'),'F','M') this gives me result - MMMMMM which i donot what i want the output to be FMFMFM Need your help D.Mahesh

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• SQL query to get latest record for all distinct items in a table

  - by David Buckley

  I have a table of all sales defined like: mysql> describe saledata; +-------------------+---------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------------------+---------------------+------+-----+---------+-------+ | SaleDate | datetime | NO | | NULL | | | StoreID | bigint(20) unsigned | NO | | NULL | | | Quantity | int(10) unsigned | NO | | NULL | | | Price | decimal(19,4) | NO | | NULL | | | ItemID | bigint(20) unsigned | NO | | NULL | | +-------------------+---------------------+------+-----+---------+-------+ I need to get the last sale price for all items (as the price may change). I know I can run a query like: SELECT price FROM saledata WHERE itemID = 1234 AND storeID = 111 ORDER BY saledate DESC LIMIT 1 However, I want to be able to get the last sale price for all items (the ItemIDs are stored in a separate item table) and insert them into a separate table. How can I get this data? I've tried queries like this: SELECT storeID, itemID, price FROM saledata WHERE itemID IN (SELECT itemID from itemmap) ORDER BY saledate DESC LIMIT 1 and then wrap that into an insert, but it's not getting the proper data. Is there one query I can run to get the last price for each item and insert that into a table defined like: mysql> describe lastsale; +-------------------+---------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------------------+---------------------+------+-----+---------+-------+ | StoreID | bigint(20) unsigned | NO | | NULL | | | Price | decimal(19,4) | NO | | NULL | | | ItemID | bigint(20) unsigned | NO | | NULL | | +-------------------+---------------------+------+-----+---------+-------+

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• how to convert Database Hierarchical Data to XML using ASP.net 3.5 and LINQ

  - by mahdiahmadirad

  hello guys! i have a table with hierarchical structure. like this: and table data shown here: this strategy gives me the ability to have unbounded categories and sub-categories. i use ASP.net 3.5 SP1 and LINQ and MSSQL Server2005. How to convert it to XML? I can Do it with Dataset Object and ".GetXML()" method. but how to implement it with LINQtoSQL or LINQtoXML??? or if there is another simpler way to perform that? what is your suggestion? the best way? I searched the web but found nothing for .net 3.5 featuers.

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• SQLite long to wide formats?

  - by Stephen

  Hi, I wonder if there is a canonical way to convert data from long to wide format in SQLite (is that operation usually in the domain of relational databases?). I tried to follow this example for MySQL but I guess SQLite does not have the same IF construct... Thanks!

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• How to convert from varbinary to char/varchar in mysql

  - by Saeros

  Hi I have a field which is varbinary. It has already been populated. Now how do i convert varbinary to varchar so that I can use the data in the field for some other purpose. I use a MySQL version 5.10

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• How to escape strings in MSSQL using PHP?

  - by Click Upvote

  I'm looking for the alternative of mysql_real_escape_string() for MSSQL. Is addslashes() my best option or there is another alternative function that can be used? Edit: Alternative for mysql_error() would also be useful.

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