An acronym for "Structured Query Language" (it's not the name of a specific DBMS product), SQL can be used in relational database management systems (RDBMS) to query, update, delete, and insert data as well as modify the structure of the database. It can also be used to manage schemas and data ...

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Why do primary keys have names of their own?

From a mathematical view, granted that a table has at most one primary key, it seems to be a shortsighted design decision to refer to primary keys by some arbitrary name instead of a simple table ...
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3answers
6k views

How does shrinking a SQL Server log file affect performance?

I have a SQL Server 2008 database that has a data file of some 2GB in size, but the log file is over 8GB. With pre-2008 databases I could use the 'Backup log' and the TRUNCATE_ONLY option but this is ...
13
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3answers
7k views

PostgreSQL multi-column unique constraint and NULL values

I have a table like the following: create table my_table ( id int8 not null, id_A int8 not null, id_B int8 not null, id_C int8 null, constraint pk_my_table primary key (id), constraint ...
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5answers
647 views

Needing A Database Design Book

I am designing a database and it has so many relationships among my tables and i need a book that teaches database design very well.I am looking for a book where table relationships simple and complex ...
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4answers
2k views

What is the significance of a semicolon at the end of SQL*Plus commands?

Some statements like create table, insert into etc take a semicolon at the end: CREATE TABLE employees_demo ( employee_id NUMBER(6) , first_name VARCHAR2(20) , last_name ...
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3answers
323 views

What is the correct result for this query?

I came across this puzzle in the comments here CREATE TABLE r (b INT); SELECT 1 FROM r HAVING 1=1; SQL Server and PostgreSQL return 1 row. MySQL and Oracle return zero rows. Which is correct? ...
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2answers
285 views

Does firing off an indefinite WAITFOR increase the log file size?

In the last release of my app, I added a command that tells it to wait when something arrives in the Service Broker queue: WAITFOR (RECEIVE CONVERT(int, message_body) AS Message FROM MyQueue) The ...
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3answers
17k views

How to find the latest SQL statements within the database?

I like to get the latest executed statements within my database, along with performance indicators. As such, I like to know, which SQL statements were most CPU/DISK intensive.
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1answer
2k views

How to get the MAX row

In SQL Server I've always found it a pain to get the max rows for a dataset, I'm looking for a list of the methods to retrieve the max rows with some guidance on performance and maintainability. ...
13
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1answer
756 views

Sql Anywhere 11: Restoring incremental backup failure

We want to create remote incremental backups after a full backup. This will allow us to restore in the event of a failure and bring up another machine with as close to real time backups as possible ...
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4answers
1k views

Why use WHERE 1 or WHERE 1=1?

Usually, if conditions are not required in our query statements, we don't use a WHERE clause. But I see a WHERE 1 clause being used in many places, even where other conditions are not present. Why ...
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2answers
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How to pass in parameters to a SQL Server script called with sqlcmd? [closed]

Is it possible to pass parameters to a SQL Server script? I have a script that creates a database. It is called from a batch file using sqlcmd. Part of that SQL script is as follows: CREATE DATABASE ...
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2answers
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How do I map an IS-A relationship into a database?

Consider the following: entity User { autoincrement uid; string(20) name; int privilegeLevel; } entity DirectLoginUser { inherits User; string(20) username; string(16) ...
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1answer
754 views

What does collation mean in database parlance?

I am learning sqlite from a book which has mentioned collation and collating sequence multiple times. What does it mean exactly in the database world ?
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5answers
1k views

Sequential GUID or bigint for 'huge' database table PK

I know this type of question comes up a lot, but I've yet to read any compelling arguments to help me make this decision. Please bear with me! I have a huge database - it grows by about 10,000,000 ...
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2answers
128 views

What programming language is this?

:#PCA=Campaign//CampId//CampDesc//CampBusId = 2 :#PE=PubEdition//EdId//EdCode//EdCampId = :#PCA :#PCT=ContactType//ContTypeCd//ContTypeDesc//ContTypeUsrId in (21, 25) ...
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2answers
2k views

Performance Tuning for Huge Table (SQL Server 2008 R2)

Background: I have a fact table in UAT Phase. Objective to load 5 yrs of data in Prod (expected size 400 Mn records). Currently it has only 2 years of data in Test. Table Features: No of ...
12
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2answers
5k views

MySQL: Tree-Hierarchical query

SUB-TREE WITHIN A TREE in MySQL In my MYSQL Database COMPANY, I have a Table: Employee with recursive association, an employee can be boss of other employee. A self relationship of kind (SuperVisor ...
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2answers
411 views

SQL Server 2008 Performance issue with very strange resolution

I'm a long time DBA (12 years in SQL). I'm running SQL Server 2008 Enterprise in a Win 2008 clustered environment. 128gb memory and 32cpu in each cluster node. Not wimpy. I've got the weirdest ...
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7answers
1k views

How to query a database for empty tables

Due to some 'developers' we had working on our system we have had issues with empty tables. We have found that during the transfer to the cloud several tables were copied, but the data in them ...
11
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2answers
2k views

Is it a bad practice to always create a transaction?

Is it a bad practice to always create a transaction? For example, it is a good practice to create a transaction for nothing but one simple SELECT? What is the cost of creating a transaction when it ...
11
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4answers
19k views

How to add sysadmin to user in SQL Server 2008 when no sysadmin accounts exist

I have a SQL server 2008 instance running. Unfortunately during testing I deselected the sysadmin rights for my login and now can't readd it (because I don't have sysadmin rights). There are no other ...
11
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1answer
507 views

GO After every T-SQL statement

What is the reasoning behind using the GO statement after every SQL statement? I understand that GO signals the end of batch and/or allows the reputation of statements but what advantage does it have ...
11
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1answer
385 views

Is using DISTINCT as a hint in subqueries useful?

Does adding DISTINCT in the following example have any impact on the query running time? Is it wise to use it as a hint sometimes? SELECT * FROM A WHERE A.SomeColumn IN (SELECT DISTINCT ...
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2answers
24k views

Sql Server database in recovery: How to stop, Take ofline or delete?

I have a development database which has entered recovery mode on restart, and has been recovering for the last hour or so. I need to either stop the recovery, or kill it in some way. I dont care one ...
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2answers
2k views

System disk run out of space when running heavy SQL queries on SQL Server 2012

I'm quite new to SQL Server 2012, I would be grateful if someone can help. I have restored a copy of a huge database to SQL Server 2012 and I tried to run some simple queries against it. I'm trying ...
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4answers
641 views

Creating centralized DBA database

We have 200+ servers and I am thinking about creating a centralized DBA database where it logs backup, errors, space jobs and generate reports on SSRS. I am not sure where to start and I would highly ...
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1answer
2k views

Patterns for setting up sharding for SQL Server 2008 R2, in order to handle large datasets?

I want to handle a large dataset (> 1 billion rows) in SQL Server 2008 R2. I heard that if you set up "sharding" or "horizontal partitioning", it makes it quicker to handle large datasets as it breaks ...
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5answers
2k views

Efficiently select beginning and end of multiple contiguous ranges in Postgresql query

I've got about a billion rows of data in a table with a name and an integer in the range 1-288. For a given name, every int is unique, and not every possible integer in the range is present--so there ...
11
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1answer
4k views

How do I read Query Cost, and is it always a percentage?

I'm currently studying for SQL 70-433 (the Microsoft Certification exam), and I'm getting very confused about the "query cost" performance metric. According to any documentation I could find via ...
11
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1answer
223 views

Why does subquery use parallelism and join doesn't?

Why does SQL server use parallelism when running this query which uses a subquery but it doesn't when using a join? The join version runs in serial and takes around 30 times longer to complete. Join ...
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3answers
1k views

Why does my ORDER BY sort two tables before the EXCEPT (slow) and not after (fast)?

SQL server 2008 R2 query optimizer puzzle We have two tables, both containing 9 million rows. 70.000 rows are different, the others are the same. This is fast, 13 seconds, select * from bigtable1 ...
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7answers
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How do I Create Tablespace in Oracle 11g?

I am not too savvy in Oracle, and I have been trying to create a TABLESPACE, which keep on giving me an error message of invalid file name. Below is the syntax that I have used: SQL> create ...
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3answers
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Does “WHERE 1=1” usually have an impact on query performance?

I recently saw the question "where 1=1 statement"; a SQL construct I have used often in constructing dynamic SQL in an effort to write cleaner code (from the perspective of the host language). ...
10
votes
4answers
2k views

Is it possible to increase query performance on a narrow table with millions of rows?

I have a query that is currently taking an average of 2500ms to complete. My table is very narrow, but there are 44 million rows. What options do I have to improve performance, or is this as good as ...
10
votes
3answers
382 views

Can IS DISTINCT FROM be combined with ANY or ALL somehow?

Is a postgres way of combining IS DISTINCT FROM with ANY or some other neat way of getting the same result? select count(*) from (select 'A' foo union all select 'Z' union all select null) z where ...
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3answers
4k views

Should I use SQL JOIN or IN Clause?

I have a question about best approach. I am not sure which approach is best when data is considered variable in size. Consider the following 3 TABLES: EMPLOYEE EMPLOYEE_ID, EMP_NAME PROJECT ...
10
votes
4answers
41k views

How to update a table from a another table

I have one table A has column (id, field_1,field_2), and another table B has column (id,field_2) Now I want to merge table B to A, that means i want to update field_2 in table A to value of table B. ...
10
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2answers
368 views

Decision criteria on when to use a non-dbo schema vs a new Database

I'm mostly an application developer but find myself having to do all the up-front database work for my current project (btw... its MS SQL Server 2008). As a first decision, I'm trying to figure out ...
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3answers
1k views

Updating a table with millions of records, its been 4 days

I am currently updating a table with millions of records, its been 4 days and query is still executing. I checked the activity monitor its shows that query is running. In event log there is no ...
10
votes
1answer
727 views

Why does NOT IN with a set containing NULL always return FALSE/NULL?

I had a query (for Postgres and Informix) with a NOT IN clause containing a subquery that in some cases returned NULL values, causing that clause (and the entire query) to fail to return anything. ...
10
votes
1answer
9k views

Difference between Hash, Merge and Loop join?

In SQL Server you can specify the join hints: HASH JOIN MERGE JOIN LOOP JOIN What is the definition of those three join hints, and when should each be used?
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3answers
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Choosing a database for storing large amount of data and allowing for thousands of writes

I am working on a project that has some serious requirements regarding its database and having hard time choosing the best solution. The details are: Database will easily reach tens of terabytes of ...
10
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1answer
835 views

Generate an exception with a Context

When PostgreSQL throws an exception, there is a line "CONTEXT" like: ERROR: INSERT has more target COLUMNS than expressions LINE 3: ... ...
10
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4answers
2k views

Table partitioning for archiving data

Scenario: two databases: DB_A and DB_Archive with one very big table called tableA. every day, records older than 60 days are deleted from DB_A and moved to DB_Archive mainly to leave thing ...
10
votes
3answers
3k views

Best way to design tournament database

I'm creating a webpage for placing bets on all matches of the upcoming Euro 2012 football tournament. Need some help deciding what approach to take for the knockout phase. I have created a mockup ...
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3answers
708 views

Use MySQL to regularly do multi-way joins on 100+ GB tables?

Background: I’ve created a web application that I would like to be able to scale reasonably well. I know I'm not Google or Twitter, but my app uses a fairly large amount of data for each user and thus ...
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1answer
6k views

Stored Procedure to return dynamically created table data

Quick back story, we are working with an outside vendor that has a survey system. The system is not necessarily designed the best in that when you create a new survey and the system creates a new ...
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4answers
2k views

Benefits of using backtick (`) in MySQL queries?

In MySQL we can create queries with or without the backtick (`) symbol. Example: SELECT * FROM TEST; SELECT * FROM `TEST`; Both works fine in mysql-console. Is there any technical difference ...
9
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3answers
380 views

Are these two queries logically equivalent?

Are these two queries logically equivalent? DECLARE @DateTime DATETIME = GETDATE() Query 1 SELECT * FROM MyTable WHERE Datediff(DAY, LogInsertTime, @DateTime) > 7 Query 2 SELECT * FROM ...