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  • SQLite - a smart way to remove and add new objects

    - by Ilya
    Hi, I have a table in my database and I want for each row in my table to have an unique id and to have the rows named sequently. For example: I have 10 rows, each has an id - starting from 0, ending at 9. When I remove a row from a table, lets say - row number 5, there occurs a "hole". And afterwards I add more data, but the "hole" is still there. It is important for me to know exact number of rows and to have at every row data in order to access my table arbitrarily. There is a way in sqlite to do it? Or do I have to manually manage removing and adding of data? Thank you in advance, Ilya.

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  • Selenium Testing

    - by Joakim
    Hi I want to get a bunch of dom-objects with xpath and loop through those to check if they contains a specified text, is this possible in the Selenium IDE or rc? Perl is my prefered language XPath would be something like xpath=//tbody[@class='table-data']/tr/td/div[@class='table-item'] This would return all row items in the table, but i need to check each div if contains a specified text string. Is this possible with Selenium? Best regards

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  • Android: database reading problem throws exception

    - by Vamsi
    Hi, i am having this problem with the android database. I adopted the DBAdapter file the NotepadAdv3 example from the google android page. DBAdapter.java public class DBAdapter { private static final String TAG = "DBAdapter"; private static final String DATABASE_NAME = "PasswordDb"; private static final String DATABASE_TABLE = "myuserdata"; private static final String DATABASE_USERKEY = "myuserkey"; private static final int DATABASE_VERSION = 2; public static final String KEY_USERKEY = "userkey"; public static final String KEY_TITLE = "title"; public static final String KEY_DATA = "data"; public static final String KEY_ROWID = "_id"; private final Context mContext; private DatabaseHelper mDbHelper; private SQLiteDatabase mDb; private static final String DB_CREATE_KEY = "create table " + DATABASE_USERKEY + " (" + "userkey text not null" +");"; private static final String DB_CREATE_DATA = "create table " + DATABASE_TABLE + " (" + "_id integer primary key autoincrement, " + "title text not null" + "data text" +");"; private static class DatabaseHelper extends SQLiteOpenHelper { DatabaseHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); } @Override public void onCreate(SQLiteDatabase db) { db.execSQL(DB_CREATE_KEY); db.execSQL(DB_CREATE_DATA); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { Log.w(TAG, "Upgrading database from version " + oldVersion + " to " + newVersion + ", which will destroy all old data"); db.execSQL("DROP TABLE IF EXISTS myuserkey"); db.execSQL("DROP TABLE IF EXISTS myuserdata"); onCreate(db); } } public DBAdapter(Context ctx) { this.mContext = ctx; } public DBAdapter Open() throws SQLException{ try { mDbHelper = new DatabaseHelper(mContext); } catch(Exception e){ Log.e(TAG, e.toString()); } mDb = mDbHelper.getWritableDatabase(); return this; } public void close(){ mDbHelper.close(); } public Long storeKey(String userKey){ ContentValues initialValues = new ContentValues(); initialValues.put(KEY_USERKEY, userKey); try { mDb.delete(DATABASE_USERKEY, "1=1", null); } catch(Exception e) { Log.e(TAG, e.toString()); } return mDb.insert(DATABASE_USERKEY, null, initialValues); } public String retrieveKey() { final Cursor c; try { c = mDb.query(DATABASE_USERKEY, new String[] { KEY_USERKEY}, null, null, null, null, null); }catch(Exception e){ Log.e(TAG, e.toString()); return ""; } if(c.moveToFirst()){ return c.getString(0); } else{ Log.d(TAG, "UserKey Empty"); } return ""; } //not including any function related to "myuserdata" table } Class1.java { mUserKey = mDbHelper.retrieveKey(); mDbHelper.storeKey(Key); } the error that i am receiving is from Log.e(TAG, e.toString()) in the methods retrieveKey() and storeKey() "no such table: myuserkey: , while compiling: SELECT userkey FROM myuserkey"

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  • SQL (mySQL) update some value in all records processed by a select

    - by jdmuys
    I am using mySQL from their C API, but that shouldn't be relevant. My code must process records from a table that match some criteria, and then update the said records to flag them as processed. The lines in the table are modified/inserted/deleted by another process I don't control. I am afraid in the following, the UPDATE might flag some records erroneously since the set of records matching might have changed between step 1 and step 3. SELECT * FROM myTable WHERE <CONDITION>; # step 1 <iterate over the selected set of lines. This may take some time.> # step 2 UPDATE myTable SET processed=1 WHERE <CONDITION> # step 3 What's the smart way to ensure that the UPDATE updates all the lines processed, and only them? A transaction doesn't seem to fit the bill as it doesn't provide isolation of that sort: a recently modified record not in the originally selected set might still be targeted by the UPDATE statement. For the same reason, SELECT ... FOR UPDATE doesn't seem to help, though it sounds promising :-) The only way I can see is to use a temporary table to memorize the set of rows to be processed, doing something like: CREATE TEMPORARY TABLE workOrder (jobId INT(11)); INSERT INTO workOrder SELECT myID as jobId FROM myTable WHERE <CONDITION>; SELECT * FROM myTable WHERE myID IN (SELECT * FROM workOrder); <iterate over the selected set of lines. This may take some time.> UPDATE myTable SET processed=1 WHERE myID IN (SELECT * FROM workOrder); DROP TABLE workOrder; But this seems wasteful and not very efficient. Is there anything smarter? Many thanks from a SQL newbie.

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  • SQL SELECT: "Give me all documents where all of the documents procedures are 'work in progress'"

    - by prestonmarshall
    This one really has me stumped. I have a documents table which hold info about the documents, and a procedures table, which is kind of like a revisions table for each document. What I need to do is write a select statement which gives me all of the documents where all of the procedures have the status "work_in_progress". Here's an example procedures table: document_id | status 1 | 'wip' 1 | 'wip' 1 | 'wip' 1 | 'approved' 2 | 'wip' 2 | 'wip' 2 | 'wip' Here, I would want my query to only return document id 2, because all of its statuses are work_in_progress. I DO NOT want document_id 1 since one of its statuses is 'approved'. I believe this is relational division I want, but I'm not sure where to start. This is MySQL 5.0 FYI.

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  • Duplicate entries on mysql on insert using doctrine

    - by Nikos Galis
    Hi all! I am facing a very weird problem with mysql and doctrine [with help of codeIgniter]. I am trying to make a simple migration script taking all records from one table and after a little process, saving them to another. However, on my laptop [running windows and wamp] I get double numbers of the original table records to have been copied to the destination table. In my colleagues' laptops, everything works fine! We are all using mysql 5.0.86 [plus windows plus wamp]. Here is the code : function buggy_function(){ $this->db(); //get db connection $q = Doctrine_Query::create()->from('Oldtable r'); $oldrecords = $q->fetchArray(); $count = 0; foreach ($oldrecords as $oldrecord){ $newrecord = new NewTableClass(); $newrecord->password = md5($oldrecord['password']); $newrecord->save(); echo $newrecord->id. ' Id -> saved.' } } Simple as that! I have 39 records on the Old table and I am getting 78 records in the new table, which are exactly the same records, except from the unique primary key. It seems as if the script runs twice. But the output of the script is the following : 1 Id -> saved. 2 Id -> saved. ... ... 39 Id -> saved. Do you have any idea why this is happening? Any known bug for mysql? Thank you in advanced!'

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  • SQL deadlock on delete then bulk insert

    - by StarLite
    I have an issue with a deadlock in SQL Server that I haven't been able to resolve. Basically I have a large number of concurrent connections (from many machines) that are executing transactions where they first delete a range of entries and then re-insert entries within the same range with a bulk insert. Essentially, the transaction looks like this BEGIN TRANSACTION T1 DELETE FROM [TableName] WITH( XLOCK HOLDLOCK ) WHERE [Id]=@Id AND [SubId]=@SubId INSERT BULK [TableName] ( [Id] Int , [SubId] Int , [Text] VarChar(max) COLLATE SQL_Latin1_General_CP1_CI_AS ) WITH(CHECK_CONSTRAINTS, FIRE_TRIGGERS) COMMIT TRANSACTION T1 The bulk insert only inserts items matching the Id and SubId of the deletion in the same transaction. Furthermore, these Id and SubId entries should never overlap. When I have enough concurrent transaction of this form, I start to see a significant number of deadlocks between these statements. I added the locking hints XLOCK HOLDLOCK to attempt to deal with the issue, but they don't seem to be helpling. The canonical deadlock graph for this error shows: Connection 1: Holds RangeX-X on PK_TableName Holds IX Page lock on the table Requesting X Page lock on the table Connection 2: Holds IX Page lock on the table Requests RangeX-X lock on the table What do I need to do in order to ensure that these deadlocks don't occur. I have been doing some reading on the RangeX-X locks and I'm not sure I fully understand what is going on with these. Do I have any options short of locking the entire table here?

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  • MS SQL share identitiy seed amongst tables

    - by Net Citizen
    In MS SQL is it possible to share an identity seed across tables? For example I may have 2 tables: Table: PeopleA id name Table: PeopleB id name I'd like for PeopleA.id and PeopleB.id to always have unique values between themselves. I.e. I want them to share the same Identity seed. Note: I do not want to hear about table partitioning please, only about if it's possible to share a seed across tables.

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  • When I make a database change, how do I know what needs to be removed and readded to the LinqToSql O

    - by Michael Maddox
    For example, I alter a column in a table to be not null from null. I need to then delete and readd the table. That part is pretty clear. What about views, functions, and stored procedures that access the table, especially that column in the table? I've tried running diffs against the files generated by SQLMetal with some limited success, but even with that it's fairly unclear. I know there is at least one commercial tool out there that claims to address this problem, but I am looking for something free. How are people dealing with this issue?

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  • Mysql - Summary Tables

    - by jwzk
    Which method do you suggest and why? Creating a summary table and . . . 1) Updating the table as the action occurs in real time. 2) Running group by queries every 15 minutes to update the summary table. 3) Something else? The data must be near real time, it can't wait an hour, a day, etc.

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  • Need help with Xpath methods in javascript (selectSingleNode, selectNodes)

    - by Andrija
    I want to optimize my javascript but I ran into a bit of trouble. I'm using XSLT transformation and the basic idea is to get a part of the XML and subquery it so the calls are faster and less expensive. This is a part of the XML: <suite> <table id="spis" runat="client"> <rows> <row id="spis_1"> <dispatch>'2008', '288627'</dispatch> <data col="urGod"> <title>2008</title> <description>Ur. god.</description> </data> <data col="rbr"> <title>288627</title> <description>Rbr.</description> </data> ... </rows> </table> </suite> In the page, this is the javascript that works with this: // this is my global variable for getting the elements so I just get the most // I can in one call elemCollection = iDom3.Table.all["spis"].XML.DOM.selectNodes("/suite/table/rows/row").context; //then I have the method that uses this by getting the subresults from elemCollection //rest of the method isn't interesting, only the selectNodes call _buildResults = function (){ var _RowList = elemCollection.selectNodes("/data[@col = 'urGod']/title"); var tmpResult = ['']; var substringResult=""; for (i=0; i<_RowList.length; i++) { tmpResult.push(_RowList[i].text,iDom3.Global.Delimiter); } ... //this variant works elemCollection = iDom3.Table.all["spis"].XML.DOM _buildResults = function (){ var _RowList = elemCollection.selectNodes("/suite/table/rows/row/data[@col = 'urGod']/title"); var tmpResult = ['']; var substringResult=""; for (i=0; i<_RowList.length; i++) { tmpResult.push(_RowList[i].text,iDom3.Global.Delimiter); } ... The problem is, I can't find a way to use the subresults to get what I need.

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  • Query doesn't use a covering-index when applicable

    - by Dor
    I've downloaded the employees database and executed some queries for benchmarking purposes. Then I noticed that one query didn't use a covering index, although there was a corresponding index that I created earlier. Only when I added a FORCE INDEX clause to the query, it used a covering index. I've uploaded two files, one is the executed SQL queries and the other is the results. Can you tell why the query uses a covering-index only when a FORCE INDEX clause is added? The EXPLAIN shows that in both cases, the index dept_no_from_date_idx is being used anyway. To adapt myself to the standards of SO, I'm also writing the content of the two files here: The SQL queries: USE employees; /* Creating an index for an index-covered query */ CREATE INDEX dept_no_from_date_idx ON dept_emp (dept_no, from_date); /* Show `dept_emp` table structure, indexes and generic data */ SHOW TABLE STATUS LIKE "dept_emp"; DESCRIBE dept_emp; SHOW KEYS IN dept_emp; /* The EXPLAIN shows that the subquery doesn't use a covering-index */ EXPLAIN SELECT SQL_NO_CACHE * FROM dept_emp INNER JOIN ( /* The subquery should use a covering index, but isn't */ SELECT SQL_NO_CACHE emp_no, dept_no FROM dept_emp WHERE dept_no="d001" ORDER BY from_date DESC LIMIT 20000,50 ) AS `der` USING (`emp_no`, `dept_no`); /* The EXPLAIN shows that the subquery DOES use a covering-index, thanks to the FORCE INDEX clause */ EXPLAIN SELECT SQL_NO_CACHE * FROM dept_emp INNER JOIN ( /* The subquery use a covering index */ SELECT SQL_NO_CACHE emp_no, dept_no FROM dept_emp FORCE INDEX(dept_no_from_date_idx) WHERE dept_no="d001" ORDER BY from_date DESC LIMIT 20000,50 ) AS `der` USING (`emp_no`, `dept_no`); The results: -------------- /* Creating an index for an index-covered query */ CREATE INDEX dept_no_from_date_idx ON dept_emp (dept_no, from_date) -------------- Query OK, 331603 rows affected (33.95 sec) Records: 331603 Duplicates: 0 Warnings: 0 -------------- /* Show `dept_emp` table structure, indexes and generic data */ SHOW TABLE STATUS LIKE "dept_emp" -------------- +----------+--------+---------+------------+--------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-----------------+----------+----------------+---------+ | Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time | Update_time | Check_time | Collation | Checksum | Create_options | Comment | +----------+--------+---------+------------+--------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-----------------+----------+----------------+---------+ | dept_emp | InnoDB | 10 | Compact | 331883 | 36 | 12075008 | 0 | 21544960 | 29360128 | NULL | 2010-05-04 13:07:49 | NULL | NULL | utf8_general_ci | NULL | | | +----------+--------+---------+------------+--------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-----------------+----------+----------------+---------+ 1 row in set (0.47 sec) -------------- DESCRIBE dept_emp -------------- +-----------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-----------+---------+------+-----+---------+-------+ | emp_no | int(11) | NO | PRI | NULL | | | dept_no | char(4) | NO | PRI | NULL | | | from_date | date | NO | | NULL | | | to_date | date | NO | | NULL | | +-----------+---------+------+-----+---------+-------+ 4 rows in set (0.05 sec) -------------- SHOW KEYS IN dept_emp -------------- +----------+------------+-----------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | +----------+------------+-----------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | dept_emp | 0 | PRIMARY | 1 | emp_no | A | 331883 | NULL | NULL | | BTREE | | | dept_emp | 0 | PRIMARY | 2 | dept_no | A | 331883 | NULL | NULL | | BTREE | | | dept_emp | 1 | emp_no | 1 | emp_no | A | 331883 | NULL | NULL | | BTREE | | | dept_emp | 1 | dept_no | 1 | dept_no | A | 7 | NULL | NULL | | BTREE | | | dept_emp | 1 | dept_no_from_date_idx | 1 | dept_no | A | 13 | NULL | NULL | | BTREE | | | dept_emp | 1 | dept_no_from_date_idx | 2 | from_date | A | 165941 | NULL | NULL | | BTREE | | +----------+------------+-----------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 6 rows in set (0.23 sec) -------------- /* The EXPLAIN shows that the subquery doesn't use a covering-index */ EXPLAIN SELECT SQL_NO_CACHE * FROM dept_emp INNER JOIN ( /* The subquery should use a covering index, but isn't */ SELECT SQL_NO_CACHE emp_no, dept_no FROM dept_emp WHERE dept_no="d001" ORDER BY from_date DESC LIMIT 20000,50 ) AS `der` USING (`emp_no`, `dept_no`) -------------- +----+-------------+------------+--------+----------------------------------------------+-----------------------+---------+------------------------+-------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+------------+--------+----------------------------------------------+-----------------------+---------+------------------------+-------+-------------+ | 1 | PRIMARY | <derived2> | ALL | NULL | NULL | NULL | NULL | 50 | | | 1 | PRIMARY | dept_emp | eq_ref | PRIMARY,emp_no,dept_no,dept_no_from_date_idx | PRIMARY | 16 | der.emp_no,der.dept_no | 1 | | | 2 | DERIVED | dept_emp | ref | dept_no,dept_no_from_date_idx | dept_no_from_date_idx | 12 | | 21402 | Using where | +----+-------------+------------+--------+----------------------------------------------+-----------------------+---------+------------------------+-------+-------------+ 3 rows in set (0.09 sec) -------------- /* The EXPLAIN shows that the subquery DOES use a covering-index, thanks to the FORCE INDEX clause */ EXPLAIN SELECT SQL_NO_CACHE * FROM dept_emp INNER JOIN ( /* The subquery use a covering index */ SELECT SQL_NO_CACHE emp_no, dept_no FROM dept_emp FORCE INDEX(dept_no_from_date_idx) WHERE dept_no="d001" ORDER BY from_date DESC LIMIT 20000,50 ) AS `der` USING (`emp_no`, `dept_no`) -------------- +----+-------------+------------+--------+----------------------------------------------+-----------------------+---------+------------------------+-------+--------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+------------+--------+----------------------------------------------+-----------------------+---------+------------------------+-------+--------------------------+ | 1 | PRIMARY | <derived2> | ALL | NULL | NULL | NULL | NULL | 50 | | | 1 | PRIMARY | dept_emp | eq_ref | PRIMARY,emp_no,dept_no,dept_no_from_date_idx | PRIMARY | 16 | der.emp_no,der.dept_no | 1 | | | 2 | DERIVED | dept_emp | ref | dept_no_from_date_idx | dept_no_from_date_idx | 12 | | 37468 | Using where; Using index | +----+-------------+------------+--------+----------------------------------------------+-----------------------+---------+------------------------+-------+--------------------------+ 3 rows in set (0.05 sec) Bye

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  • Can you notice what's wrong with my PHP or MYSQL code?

    - by Jenna
    I am trying to create a category menu with sub categories. I have the following MySQL table: -- -- Table structure for table `categories` -- CREATE TABLE IF NOT EXISTS `categories` ( `ID` int(11) NOT NULL AUTO_INCREMENT, `name` varchar(1000) NOT NULL, `slug` varchar(1000) NOT NULL, `parent` int(11) NOT NULL, `type` varchar(255) NOT NULL, PRIMARY KEY (`ID`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=66 ; -- -- Dumping data for table `categories` -- INSERT INTO `categories` (`ID`, `name`, `slug`, `parent`, `type`) VALUES (63, 'Party', '/category/party/', 0, ''), (62, 'Kitchen', '/category/kitchen/', 61, 'sub'), (59, 'Animals', '/category/animals/', 0, ''), (64, 'Pets', '/category/pets/', 59, 'sub'), (61, 'Rooms', '/category/rooms/', 0, ''), (65, 'Zoo Creatures', '/category/zoo-creatures/', 59, 'sub'); And the following PHP: <?php include("connect.php"); echo "<ul>"; $query = mysql_query("SELECT * FROM categories"); while ($row = mysql_fetch_assoc($query)) { $catId = $row['id']; $catName = $row['name']; $catSlug = $row['slug']; $parent = $row['parent']; $type = $row['type']; if ($type == "sub") { $select = mysql_query("SELECT name FROM categories WHERE ID = $parent"); while ($row = mysql_fetch_assoc($select)) { $parentName = $row['name']; } echo "<li>$parentName >> $catName</li>"; } else if ($type == "") { echo "<li>$catName</li>"; } } echo "</ul>"; ?> Now Here's the Problem, It displays this: * Party * Rooms >> Kitchen * Animals * Animals >> Pets * Rooms * Animals >> Zoo Creatures I want it to display this: * Party * Rooms >> Kitchen * Animals >> Pets >> Zoo Creatures Is there something wrong with my loop? I just can't figure it out.

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  • Is my approach correct to replicate this form with Reportlab?

    - by Wes
    I need to generate the form seen here using Python/reportlab. http://www.flickr.com/photos/49740282@N06/4563137758/sizes/o/ I am attempting to do this by creating a custom flowable for the header at the top (with the boxes drawn) and then having a table flowable for the jewelry table below. What shows as the JEWELRY table for this example could potentially be multiple tables. I am having trouble getting my drawn header to "flow". It gets drawn, but then my table data overlays it instead of appearing below it. This is my first project with reportlab. Before I really get into debugging this, I would like to know from someone with reportlab experience if my approach is correct here. Thanks!

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  • Best practice to pass a value from pop over control on iPad.

    - by Tattat
    It is an iPad app based on SDK 3.2. I have a MainUIView, that is subclass from UIView, it have a UIButton and a UILabel. When user press the UIButton, the pop over control will be appeared with a table view. When the user select a cell from the table view, the UILabel changes content base on the user click, and the pop up table view will disappear. The question is, how can I pass the "selected cell" to the UILabel. I am thinking making a "middle man" object. When the user click the UIButton, and the "middle man" will pass to the table. When the cell is selected, the "middle man" will store the idx, and call the UILabel change content from the value of "middle man". But I think it is pretty complex to implement, is there any easier way to implement it? thz u.

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  • Sequel Migration not running up?

    - by Sleepycat
    Having some trouble with the Migrations in Sequel and could use another set of eyes. I am running a migration that looks ok but no table is created. It is definitely connecting because I can see the schema_info table has been created. -M 0/1 changes the version as you would expect but still no table. The command: sequel -m . -M 1 ~/Desktop/dbtest/testdb.yml 001_testdb.rb: class TestDb < Sequel::Migration def up create_table( "terminals") do primary_key :id Integer :location_id Integer :merchant_id BigDecimal :terminal_id, :size=>[11, 0] String :reference, :size=>255 DateTime :created_at DateTime :updated_at String :image, :default=>"default.jpg", :size=>255 end end def down drop_table :terminals end end The output in Postgres: test_db=# \dt List of relations Schema | Name | Type | Owner --------+-------------+-------+---------- public | schema_info | table | postgres (1 row) test_db=# select * from schema_info; version --------- 1 (1 row)

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  • [Newbie] How to join mysql tables

    - by Ivan
    I've an old table like this: user> id | name | address | comments And now I've to create an "alias" table to allow some users to have an alias name for some reasons. I've created a new table 'user_alias' like this: user_alias> name | user But now I have a problem due my poor SQL level... How to join both tables to generate something like this: 1 | my_name | my_address | my_comments 1 | my_alias | my_address | my_comments 2 | other_name | other_address | other_comments I mean, I want to make a "SELECT..." query that returns in the same format as the "user" table ALL users and ALL alias.. Something like this: SELECT user.* FROM user LEFT JOIN user_alias ON `user`=`id` but it doesn't work for me..

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  • If I'm updating a DataRow, do I lock the entire DataTable or just the DataRow?

    - by Dan Tao
    Suppose I'm accessing a DataTable from multiple threads. If I want to access a particular row, I suspect I need to lock that operation (I could be mistaken about this, but at least I know this way I'm safe): // this is a strongly-typed table OrdersRow row = null; lock (orderTable.Rows.SyncRoot) { row = orderTable.FindByOrderId(myOrderId); } But then, if I want to update that row, should I lock the table (or rather, the table's Rows.SyncRoot object) again, or can I simply lock the row?

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  • Database Design Primay Key, ID vs String

    - by LnDCobra
    Hi, I am currently planning to develop a music streaming application. And i am wondering what would be better as a primary key in my tables on the server. An ID int or a Unique String. Methods 1: Songs Table: SongID(int), Title(string), Artist*(string), Length(int), Album*(string) Genre Table Genre(string), Name(string) SongGenre: SongID*(int), Genre*(string) Method 2 Songs Table: SongID(int), Title(string), ArtistID*(int), Length(int), AlbumID*(int) Genre Table GenreID(int), Name(string) SongGenre: SongID*(int), GenreID*(int) Key: Bold = Primary Key, Field* = Foreign Key I'm currently designing using method 2 as I believe it will speed up lookup performance and use less space as an int takes a lot less space then a string. Is there any reason this isn't a good idea? Is there anything I should be aware of?

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  • Hibernate - how to delete bidirectional many-to-many association

    - by slomir
    Problem: I have many-to-many association between two entities A and B. I set A entity as an owner of their relationship(inverse=true is on A's collection in b.hbm.xml). When i delete an A entity, corresponding records in join table are deleted. When i delete an B entity, corresponding records in join table are not deleted (integrity violation exception). -- Let's consider some very simple example: class A{ Set<B> bset=new HashSet<B>(); //... } class B{ Set<A> aset=new HashSet<A>(); //... } File a.hbm.xml [m-to-m mappings only]: <set name="bset" table="AB"> <key name="a_id"/> <many-to-many column="b_id" class="B"/> </set> File b.hbm.xml [m-to-m mappings only]: <set name="aset" table="AB" inverse="true"> <key name="b_id"/> <many-to-many column="a_id" class="A"/> </set> Database relations: A(id,...) B(id,...) AB(a_id,b_id) Suppose that we have some records in AB joint table. For example: AB = {(1,1),(1,2)} where AB= { (a_id , b_id) | ... ... } -- Situation 1 - works probably because A is owner of AB relationship: A a=aDao.read(1); //read A entity with id=1 aDao.delete(a); //delete 'a' entity and both relations with B-entities Situation 2 - doesn't work: B b=bDao.read(1); //read B entity with id=1 bDao.delete(b); //foreign key integrity violation On the one hand, this is somehow logical to me, because the A entity is responsible for his relation with B. But, on the other hand, it is not logical or at least it is not orm-like solution that I have to explicitly delete all records in join table where concrete B entity appears, and then to delete the B entity, as I show in situation 3: Situation 3 - works, but it is not 'elegant': B b=bDao.read(1); Set<A> aset=b.getA(); //get set with A entities Iterator i=aset.iterator(); //while removes 'b' from all related A entities //while breaks relationships on A-side of relation (A is owner) while(i.hasNext()){ A a=i.next(); a.bset.remove(b); //remove entity 'b' from related 'a' entity aDao.update(a); //key point!!! this line breaks relation in database } bDao.delete(b); //'b' is deleted because there is no related A-entities -- So, my question: is there any more convenient way to delete no-owner entity (B in my example) in bidirectional many-to-many association and all of his many-to-many relations from joint table?

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  • Searching 2 fields at the same time

    - by donpal
    I have a table of first and last names firstname lastname --------- --------- Joe Robertson Sally Robert Jim Green Sandra Jordan I'm trying to search this table based on an input that consists of the full name. For example: input: Joe Robert I thought about using SELECT * FROM tablename WHERE firstname LIKE BUT the table stores the first and last name separately, so I'm not sure how to do the search in this case

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  • Why isn't my UITableView in a popover appearing in the correct scroll position?

    - by zbrimhall
    I have a split view-based app that presents a master-detail interface, and uses a popover to present the master list when in portrait mode. The popover presents a sectioned table view that ultimately gets populated by a subclass of NSFetchedResultsController. I can tap the tool bar button to present the master list, scroll to whatever row, and tap the row to dismiss the popover. My problem is that if the table is scrolled past the top of the second section, when I dismiss the popover and then later tap the toolbar button to re-present it, the table's scroll position is always set such that the first row of the second section is at the top of the list. If I haven't scrolled past the top of the second section, it correctly remembers its scroll position when the table is presented again. Similarly, in landscape mode, if I scroll the table past the top of the third section and then rotate to portrait, when I come back to landscape the scroll position is always set such that the first row of the third section is at the top of the list. I tried calling -scrollToNearestSelectedRowAtScrollPosition:animated in both the master view controller's -viewWillAppear, as well as in the split view delegate's splitViewController:popoverController:willPresentViewController:, to no effect. Anybody have a clue what I might be doing wrong?

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  • Using hash tables in racket

    - by user2963128
    Im working on an Ngrams program and im having trouble filling out my hash table. i want to write out a recursive function that will take the words and add them to the hash table. The way its supposed to work is given the data set 1 2 3 4 5 6 7 the first entry in the hash table should have a key of [1 2] and the data should be 3. The second entry should be: [2 3] and its data should be 4 and continuing on until the end of the text file. we are given a predefined function called readword that will simply return 1 word from the text. But im not sure how to make these calls overlap each other. The calls would look something like this if the data was hard coded in. (hash-set! (list "1" "2") 3 (hash-set! (list "2" "3") 4 2 calls that ive tried look like this (hash-set! Ngram-table(list((word1) (word2)) readword in))) (hash-set! Ngram-table(append((cdr data) word1)) readword in) apparently the in after readword is supposed to tell the computer that this is and input instead of an output or something like that. How would I call this to make the data in the key of the hashtable overlap like this? And what would the recursive call look like? edit: also we are not allowed to use assigment statements in this program.

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