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  • Selecting distinct values from mysql with largest timestamp

    - by user987048
    I am building a mail system. The inbox is only supposed to grab the last message (one with the highest time value) of a concatenation of user and sender, where the user or sender is the user ID. Here is the table structure: CREATE TABLE IF NOT EXISTS `mail` ( `user` int(11) NOT NULL, `sender` int(11) NOT NULL, `body` text NOT NULL, `new` enum('0','1') NOT NULL default '1', `time` int(11) NOT NULL, KEY `user` (`user`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8; So, with a table with the following data: user sender new time ***************************************** 1 0 0 5 1 0 0 6 2 1 0 7 1 0 1 8 1 2 0 9 1 0 1 11 1 2 1 12 I want to select the following: WHERE USER OR SENDER = X (in this case, 1) user sender new time ***************************************** 2 1 0 7 1 2 0 9 1 0 1 11 How would I go about doing something like this?

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  • Forcing the use of an index can improve performance?

    - by aF.
    Imagine that we have a query like this: select a.col1, b.col2 from t1 a inner join t2 b on a.col1 = b.col2 where a.col1 = 'abc' Both col1 and col2 don't have any index. If I add another restriction on the where clause, one that is always correct but with a column with an index: select a.col1, b.col2 from t1 a inner join t2 b on a.col1 = b.col2 where a.col1 = 'abc' and a.id >= 0 -- column always true and with index May the query perform faster since it may use the index on id column?

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  • Best way to get distinct values from large table

    - by derivation
    I have a db table with about 10 or so columns, two of which are month and year. The table has about 250k rows now, and we expect it to grow by about 100-150k records a month. A lot of queries involve the month and year column (ex, all records from march 2010), and so we frequently need to get the available month and year combinations (ie do we have records for april 2010?). A coworker thinks that we should have a separate table from our main one that only contains the months and years we have data for. We only add records to our main table once a month, so it would just be a small update on the end of our scripts to add the new entry to this second table. This second table would be queried whenever we need to find the available month/year entries on the first table. This solution feels kludgy to me and a violation of DRY. What do you think is the correct way of solving this problem? Is there a better way than having two tables?

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  • entering data in sql database through asp

    - by sushant
    pass=session("password") Set objIns=server.CreateObject("adodb.connection") objIns.Open session("Psrconnect") inspass="Insert into passwords(pass) values ('&pass&')" objIns.Execute(inspass) i dont know what should be the syntax to pass the value stored in the variable. with this syntax, the value entered in the database is &pass&. can anyone plz help me out?

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  • Most efficient way to Update with Linq2Sql

    - by pranay
    can I update my employee record as given in below function or i have to make query of employee collection first and than i update data public int updateEmployee(App3_EMPLOYEE employee) { DBContextDataContext db = new DBContextDataContext(); db.App3_EMPLOYEEs.Attach(employee); db.SubmitChanges(); return employee.PKEY; } or i have to do this public int updateEmployee(App3_EMPLOYEE employee) { DBContextDataContext db = new DBContextDataContext(); App3_EMPLOYEE emp = db.App3_EMPLOYEEs.Single(e => e.PKEY == employee.PKEY); db.App3_EMPLOYEEs.Attach(employee,emp); db.SubmitChanges(); return employee.PKEY; } But i dont want to use second option is there any efficient way to update data

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  • oracle query returns 4 duplicates of each row

    - by ajoe
    hello, I am Running a oracle query, it seems to work except that it returns 4 dupes of each result. here is the code: Select * from (Select a.*, rownum rnum From (SELECT NEW_USER.*, NEW_EHS_QUIZ_COMPLETE.datetime FROM NEW_USER, NEW_EHS_QUIZ_COMPLETE WHERE EXISTS(select * from NEW_EHS_QUIZ_COMPLETE where NEW_USER.id=NEW_EHS_QUIZ_COMPLETE.USER_ID) ORDER by last_name ASC ) a where rownum <= #pgtop# ) where rnum >= #pgbot# does anyone know why this isnt working properly? thanks in advance.

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  • Problems with mysql syntax

    - by user368453
    Hello everyone !! I´m trying to create a trigger on MySQL but I´m having a sintaxe problem, which I was not able to find. If someone more experient could help me it would be great (it´s the first time I use MySQL!)... The reason why I´m creating this trigger is for deleting all the orphan "labels", which has a many-to-many relation with "service_descriptor" (this two entities are linked by service_labels). The code I have is: CREATE TRIGGER trg_delete_orphan_label AFTER DELETE FOR EACH ROW ON restdb.service_labels DELETE FROM restdb.labels WHERE EXISTS (SELECT * FROM old D LEFT_JOIN restdb.service_labels SL ON SL.id_label = D.id_label AND D.id_service = SL.id_service WHERE SL.id_label IS NULL restdb.labels.id = D.SL.id_label ); Thanks in advance !

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  • MySQL: group by and IF statement

    - by notset
    By default, parent_id = 0. I want to select all records with parent_id = 0 and only the last ones with parent_id 0. I tried this, but it didn't work: SELECT * FROM `articles` IF `parent_id` > 0 THEN GROUP BY `parent_id` HAVING COUNT(`parent_id`) >= 1 END; ORDER BY `time` DESC What could be the solution?

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  • Creating a multi-row "table" as part of a SELECT

    - by Chad Birch
    I'm not really sure how to describe my question (thus the awful title), but it's related to this recent question. The problem would be easily solved if there was some way for me to create a "table" with 4 rows as part of my SELECT (to use with NOT IN or MINUS). What I mean is, I can do this: SELECT 1, 2, 3, 4; And will receive one row from the database: | 1 | 2 | 3 | 4 | But is there any way to receive the following (without using UNION, I don't really want a query that's potentially thousands of lines long with a long list)? | 1 | | 2 | | 3 | | 4 |

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  • Find Consecutive Rows & Calculate Duration

    - by MannyKo
    I have a set a of data that tells me if a couple of systems are available or not every 5 or 15 minutes increments. For now, the time increment shouldn't matter. The data looks like this: Status Time System_ID T 10:00 S01 T 10:15 S01 F 10:30 S01 F 10:45 S01 F 11:00 S01 T 11:15 S01 T 11:30 S01 F 11:45 S01 F 12:00 S01 F 12:15 S01 T 12:30 S01 F 10:00 S02 F 10:15 S02 F 10:30 S02 F 10:45 S02 F 11:00 S02 T 11:15 S02 T 11:30 S02 I want to create a view that tells when a system is NOT available (i.e. when it is F), from what time, to what time, and duration which is to - from. Desired results: System_ID From To Duration S01 10:30 11:00 00:30 S01 11:45 12:15 00:30 S02 10:00 11:00 01:00 Here is the script data: DROP SCHEMA IF EXISTS Sys_data CASCADE; CREATE SCHEMA Sys_data; CREATE TABLE test_data ( status BOOLEAN, dTime TIME, sys_ID VARCHAR(10), PRIMARY KEY (dTime, sys_ID) ); INSERT INTO test_data (status, dTime, sys_ID) VALUES (TRUE, '10:00:00', 'S01'); INSERT INTO test_data (status, dTime, sys_ID) VALUES (TRUE, '10:15:00', 'S01'); INSERT INTO test_data (status, dTime, sys_ID) VALUES (FALSE, '10:30:00', 'S01'); INSERT INTO test_data (status, dTime, sys_ID) VALUES (FALSE, '10:45:00', 'S01'); INSERT INTO test_data (status, dTime, sys_ID) VALUES (FALSE, '11:00:00', 'S01'); INSERT INTO test_data (status, dTime, sys_ID) VALUES (TRUE, '11:15:00', 'S01'); INSERT INTO test_data (status, dTime, sys_ID) VALUES (TRUE, '11:30:00', 'S01'); INSERT INTO test_data (status, dTime, sys_ID) VALUES (FALSE, '11:45:00', 'S01'); INSERT INTO test_data (status, dTime, sys_ID) VALUES (FALSE, '12:00:00', 'S01'); INSERT INTO test_data (status, dTime, sys_ID) VALUES (FALSE, '12:15:00', 'S01'); INSERT INTO test_data (status, dTime, sys_ID) VALUES (TRUE, '12:30:00', 'S01'); INSERT INTO test_data (status, dTime, sys_ID) VALUES (FALSE, '10:00:00', 'S02'); INSERT INTO test_data (status, dTime, sys_ID) VALUES (FALSE, '10:15:00', 'S02'); INSERT INTO test_data (status, dTime, sys_ID) VALUES (FALSE, '10:30:00', 'S02'); INSERT INTO test_data (status, dTime, sys_ID) VALUES (FALSE, '10:45:00', 'S02'); INSERT INTO test_data (status, dTime, sys_ID) VALUES (FALSE, '11:00:00', 'S02'); INSERT INTO test_data (status, dTime, sys_ID) VALUES (TRUE, '11:15:00', 'S02'); INSERT INTO test_data (status, dTime, sys_ID) VALUES (TRUE, '11:30:00', 'S02'); Thank you in advance!

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  • dbo in SqlServer

    - by ala
    I'm converting database from Teradata to SqlServer. I've noticed all tables and procedures are named by the prefix "dbo." (e.g. "dbo.Table1"). I would like to know if and how I can get rid of "dbo" because it would make the conversion task a lot more easier.

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  • Counting the instances of customers

    - by Mikae Combarado
    Say that I have a table with one column named CustomerId. The example of the instance of this table is : CustomerId 14 12 11 204 14 204 I want to write a query that counts the number of occurences of customer IDs. At the end, I would like to have a result like this : CustomerId NumberOfOccurences 14 2 12 1 11 1 204 2 14 1 I cannot think of a way to do this.

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  • removing comma from string array

    - by sarah
    Hi, I want to execute a query like select ID from "xyz_DB"."test" where user in ('a','b') so the corresponding code is like String s="("; for(String user:selUsers){ s+= " ' " + user + " ', "; } s+=")"; Select ID from test where userId in s; The following code is forming the value of s as ('a','b',) i want to remove the comma after the end of array how to do this ?

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  • How can I select the required records?

    - by simple
    Tables: Product: [id, name, brand_id, is_published] Brand: [id, name, is_published] Awards: [id, name] ProductAwards [product_id, award_id] How do I select the list of PUBLISHED brands along with the number of AWARDS of brand's products that are Published. I am cool with all the part except issuing the "is_published" restriction when counting Awards. I hope this is clear; can anyone just suggest where to dig?

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  • left join without duplicate values using MIN()

    - by Clipper87
    I have a table_1: id custno 1 1 2 2 3 3 and a table_2: id custno qty descr 1 1 10 a 2 1 7 b 3 2 4 c 4 3 7 d 5 1 5 e 6 1 5 f When I run this query to show the minimum order quantities from every customer: SELECT DISTINCT table_1.custno,table_2.qty,table_2.descr FROM table_1 LEFT OUTER JOIN table_2 ON table_1.custno = table_2.custno AND qty = (SELECT MIN(qty) FROM table_2 WHERE table_2.custno = table_1.custno ) Then I get this result: custno qty descr 1 5 e 1 5 f 2 4 c 3 7 d Customer 1 appears twice each time with the same minimum qty (& a different description) but I only want to see customer 1 appear once. I don't care if that is the record with 'e' as a description or 'f' as a description. How could I do this ? Thx!

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  • Is an index required for columns in ON clause?

    - by newbie
    Do I have to create an index on columns referenced in Joins? E.g. SELECT * FROM left_table INNER JOIN right_table ON left_table.foo = right_table.bar WHERE ... Should I create indexes on left_table(foo), right_table(bar), or both? I noticed different results when I used EXPLAIN (Postgresql) with and without indexes and switching around the order of the comparison (right_table.bar = left_table.foo) I know for sure that indexes are used for the left of the WHERE clause but I am wondering whether I need indexes for columns listed in ON clauses.

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  • is NATURAL JOIN any better than SELECT FROM WHERE in terms of performance ?

    - by ashy_32bit
    Today I got into a debate with my project manager about Cartesian products. He says a 'natural join' is somehow much better than using 'select from where' because the later cause the db engine to internally perform a Cartesian product but the former uses another approach that prevents this. As far as I know, the natural join syntax is not any different in anyway than 'select from where' in terms of performance or meaning, I mean you can use either based on your taste. SELECT * FROM table1,table2 WHERE table1.id=table2.id SELECT * FROM table1 NATURAL JOIN table2 please elaborate about the first query causing a Cartesian product but the second one being somehow more smart

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  • Query to check the consistency of records

    - by orunner
    I have four tables TableA: id1 id2 id3 value TableB: id1 desc TableC: id2 desc TableD: id3 desc What I need to do is to check if all combinations of id1 id2 id3 from table B C and D exist in the TableA. In other words, table A should contain all possible combinations of id1 id2 and id3 which are stored in the other three tables.

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  • Errors with parameter datatype in PostgreSql query

    - by John
    Im trying to execute a query to postgresql using the following code. It's written in C/C++ and I keep getting the following error when declaring a cursor: DECLARE CURSOR failed: ERROR: could not determine data type of parameter $1 Searching on here and on google, I can't find a solution. Can anyone find where I have made and error and why this is happening? thanks! void searchdb( PGconn *conn, char* name, char* offset ) { // Will hold the number of field in table int nFields; // Start a transaction block PGresult *res = PQexec(conn, "BEGIN"); if (PQresultStatus(res) != PGRES_COMMAND_OK) { printf("BEGIN command failed: %s", PQerrorMessage(conn)); PQclear(res); exit_nicely(conn); } // Clear result PQclear(res); printf("BEGIN command - OK\n"); //set the values to use const char *values[3] = {(char*)name, (char*)RESULTS_LIMIT, (char*)offset}; //calculate the lengths of each of the values int lengths[3] = {strlen((char*)name), sizeof(RESULTS_LIMIT), sizeof(offset)}; //state which parameters are binary int binary[3] = {0, 0, 1}; res = PQexecParams(conn, "DECLARE emprec CURSOR for SELECT name, id, 'Events' as source FROM events_basic WHERE name LIKE '$1::varchar%' UNION ALL " " SELECT name, fsq_id, 'Venues' as source FROM venues_cache WHERE name LIKE '$1::varchar%' UNION ALL " " SELECT name, geo_id, 'Cities' as source FROM static_cities WHERE name LIKE '$1::varchar%' OR FIND_IN_SET('$1::varchar%', alternate_names) != 0 LIMIT $2::int4 OFFSET $3::int4", 3, //number of parameters NULL, //ignore the Oid field values, //values to substitute $1 and $2 lengths, //the lengths, in bytes, of each of the parameter values binary, //whether the values are binary or not 0); //we want the result in text format // Fetch rows from table if (PQresultStatus(res) != PGRES_COMMAND_OK) { printf("DECLARE CURSOR failed: %s", PQerrorMessage(conn)); PQclear(res); exit_nicely(conn); } // Clear result PQclear(res); res = PQexec(conn, "FETCH ALL in emprec"); if (PQresultStatus(res) != PGRES_TUPLES_OK) { printf("FETCH ALL failed"); PQclear(res); exit_nicely(conn); } // Get the field name nFields = PQnfields(res); // Prepare the header with table field name printf("\nFetch record:"); printf("\n********************************************************************\n"); for (int i = 0; i < nFields; i++) printf("%-30s", PQfname(res, i)); printf("\n********************************************************************\n"); // Next, print out the record for each row for (int i = 0; i < PQntuples(res); i++) { for (int j = 0; j < nFields; j++) printf("%-30s", PQgetvalue(res, i, j)); printf("\n"); } PQclear(res); // Close the emprec res = PQexec(conn, "CLOSE emprec"); PQclear(res); // End the transaction res = PQexec(conn, "END"); // Clear result PQclear(res); }

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  • Limiting Subscriptions to be emailed using SSRS

    - by Graeme
    Currently, our system will do a "foreach" over all Subscriptions which are returned from the ListSubscriptions method of ReportingService and fire a Timed Subscription event so that they receive the report as an email. In our dev environment, I don't want every subscription of these reports to be sent out when we are testing. Is there a way I can create a new subscription with my own email address being used so that I receive the report? The temp subscription could then be deleted after sending. Any ideas on how to do this?

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