Oracle is a RDBMS (Relational Database Management System) created by Oracle Corporation. It supports a large number of languages and application development frameworks. Its primary languages are SQL, PL/SQL and Java. Also included is support for C (Pro*C, OCI and EXTPROC), C++ (OCCI) and Java (JDBC) ...

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Cannot drop nonexistent constraint and cannot create it either

While testing some migration scripts with a copy of production data (scripts run fine with development data) I found a curious situation. A CONSTRAINT has changed so I'm issuing DROP + ADD commands: ...
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Where can I find example databases for MySQL, SQL Server and Oracle?

I want to experiment with the 3 large database management systems. For this purpose it would be cool to have the same database (the same tables, etc.) for each of those. Where can I find sql scripts ...
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How to see list of databases in Oracle?

Is there an equivalent to MySQL SHOW DATABASES statement? Is it possible to find databases in a cluster? i.e. databases present on the network on some other system? Could I analyze the files present ...
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Is there any difference between Rem and — comments for SQL*Plus?

On SQL*Plus prompt, both Rem and -- qualify as comment indicators: Rem this is a comment -- this is also a comment create table emp ( id number primary key, name cvarchar2(40)); Is there any ...
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Oracle Shutdown Method

Shutting down a database before doing an upgrade or a patch can be done several ways. shutdown immediate; or shutdown abort; startup restrict; shutdown immediate; or shutdown abort; startup ...
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Why am I NOT getting a mutating table error in trigger?

It's (or at least was) known that you cannot use DML statements on a mutating table inside a trigger. An excerpt from the Oracle documentation: A mutating table is a table that is being modified ...
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Can I rely on functions being executed first in SQL

Please consider the following script: create or replace function f(p_limit in integer) return integer as begin set_global_context ('limit', p_limit); return p_limit; end; / create view v as ...
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large data movement

I would like to move billions of rows from schema1.table1 to new schema2.table2 where table2 is a refactored one from table1. Hence their table structure is different. both table1 and table2 are ...
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Limit the degree of parallelism (DOP) available to any query

On Oracle Exadata (11gR2), we have a relatively beefy database. cpu_count is 24 parallel_server_instances is 2 parallel_threads_per_cpu is 2 We noted, through observation in Oracle Enterprise ...
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Script out Oracle DDL in an automated fashion

Oracle SQL Developer is able to export DDL through Tools -> Database Export... This works very well, but requires manual intervention. I know of DBMS_METADATA.get_ddl(), but have found that the ...
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Updating 700 million rows to same value

I've got a data warehouse (oracle) where I need to set a column to the same value for all 700 million rows. I don't have admin access, or access to an admin, so this needs to be accomplished with ...
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Why can't I read Oracles CLOB columns via SQL-SERVER 2008 linked server?

I want to access data in an Oracle 11g database from SQL-Server 2008 I set up a linked server and when I execute select * from [Link_server_name]..Oracle_schema.Oracle_table and Oracle_table ...
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Why is a “non-single-group group function” allowed in a subselect but not on it's own?

Why does the first query not fail with the same error as the second: with w as (select 1 product_id, 10 units from dual union all select 2, 5 from dual) select sum(units) from (select product_id, ...
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SQL substitution feature in Oracle 10g

Three or four years ago I read in an Oracle blog somewhere that a DBA had used for an emergency incident resolution an Oracle 10g feature of real time SQL substitution. Basically, he configured Oracle ...
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Should date formats be specified in SQL statements?

I see code from developers using implicit date conversion. I would like a definitive answer to why they should not do this. SELECT * from dba_objects WHERE Created >= '06-MAR-2012';
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For absolute performance, is SUM faster or COUNT?

This relates to counting the number of records that match a certain condition, e.g. invoice amount > $100. I tend to prefer COUNT(CASE WHEN invoice_amount > 100 THEN 1 END) However, this is ...
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How is the default tablespace determined when creating a table?

The Tablespace parameter is optional when creating tables. Upon execution of a CREATE TABLE statement, Oracle assigns the default one if it was not defined. In the default database there is a ...
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Oracle sort varchar2 column with special characters last

How can I sort in Oracle a Varchar2 or NVarchar2 column to be in my own custom defined order. Or are any existing options available that will put letters first, then numbers, then all special ...
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I have a powerful machine with 70 GB RAM. How many Oracle instances with 20 GB can be created?

I have powerful machine with 70 GB RAM. I created one Oracle instance with 20 GB as sga_target. I am not able to create another Oracle instance with sga_target > 10G even when I keep the ...
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Feature comparison: Oracle Database and Microsoft SQL Server [closed]

Many companies have a heavy influence on market and technologies around them, and you often compare the products before you choose, e. g. I liked Oracle APEX, its flexibility and features, and we're ...
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Read ancient Oracle database into current Oracle version

An old computer with Oracle 8i is dead. We have the daily backup of the database (C:\oradata). We are unable to install this old Oracle version anywhere because we don't have the install CDs for it. ...
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Database backups in Oracle - Export the database or use other tools?

One of the "practices" that I've seen about being performed by DBA's in my organization is to treat a full database export using tools like exp / expdp as backup. Would this be a good practice ? What ...
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Column level security

I am in need of a solution to hide specific columns in a table. We have people who need to build reports against this database and specifically some of these tables with confidential information but ...
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How can I ensure that only one copy of a procedure is running in Oracle?

We have the need to ensure that only one copy of a particular procedure is running in Oracle. If it is already running and a user tries to open another, then it should error. Whats the best method ...
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Do Oracle databases use Java internally?

My question is fairly simple. Is Java used internally by Oracle in their DBMSs?
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What would I need to do to make sure my DB policies have to pass a security audit?

I have an audit coming up, and I was wondering what physical, electronic, and logical access controls an auditor would look for when auditing a database for an ERP system. I'm really new to this ...
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Oracle: How do I query a Hierarchical table?

Background This is for the construction of some views we'll be using for reporting. I have an table of locations, the key fields being "location" and "parent". The structure that these two fields ...
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How to connect to another db using stored procedures?

I need to get some data from an external db and make some calculations with it in another db, is it possible to connect to an external db from a stored procedure? Thanks guys. PS. Im using Oracle ...
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Duplicate an Oracle database user

We'll be having external auditors coming over to perform a review on our Oracle database. They will be running a tool to perform the review and for that, they require a user ID that can connect to the ...
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How do I generate a tnsnames.ora file to connect to an Oracle Database?

I have installed Oracle 11g, and I can connect as sysman to the Oracle database, but there is no tnsnames.ora file that I can find. Do I need to generate the tnsnames.ora file myself? If so, where do ...
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Is there an execution difference between a JOIN condition and a WHERE condition?

Is there a performance difference between these two example queries? Query 1: select count(*) from table1 a join table2 b on b.key_col=a.key_col where b.tag = 'Y' Query 2; select ...
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LNNVL Justification

LNNVL is an oracle built in function that returns TRUE for conditions evaluating to FALSE or UNKNOWN, and returns FALSE for conditions evaluating to TRUE. My question is what would be the benefit of ...
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What specifically does OracleBulkCopy do, and how can I optimize its performance?

To summarize the specifics: We need to stage approximately 5 million rows into a vendor (Oracle) database. Everything goes great for batches of 500k rows using OracleBulkCopy (ODP.NET), but when we ...
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How to migrate SQL Server Stored Procedures using temporary tables or table variables to Oracle?

C# developer encouraged by management to write SQL Server stored procedures often produce procedures like this create table #t1 (...); insert into #t1 Select ... from table_a where ...; insert into ...
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How can a datapump export have its resource usage limited on linux?

Doing an export of a number of users causes high CPU and I/O usage. I can mitigate the effects of the CPU usage using Resource Manager and setting the export session to a low priority group, but how ...
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How to modify an update in Oracle so it performs faster?

I have this query: UPDATE ( SELECT h.valid_through_dt, h.LAST_UPDATE_TMSTMP FROM ETL_FEE_SCH_TMP d, FEE_SCHEDULE_HISTORICAL h WHERE h.FUND_ID = d.FUND_ID AND ...
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ORDER BY using custom priorities for text columns

This is a sample table: name | cat ---------- hugo | sal bob | mgr mike | dev jeff | mgr john | dev Both name and cat being Varchar. cat reflects a category for these names, but I like to assign ...
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Does Oracle PL/SQL have a standard ASSERT routine?

I'd like to use an ASSERT routine functionally similar to the one found in other languages, i.e. a construct (be it a procedure, syntax...) ASSERT( <condition>, <msg>) such that when ...
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What does the term “projection” refer to in an SQL query (or view definition)

In Oracle's document The Query Optimizer, under View Merging, I found the following information The view merging optimization applies to views that contain only selections, projections, and ...
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If I SET ARRAYSIZE 1 in SQL*Plus, the records are still fetched in pairs. Why?

I thought about writing a simple tail -f like utility to "trace" the progress of some figures within the database: create or replace function tail_f return varchar2_tab pipelined as n number; ...
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What is the difference between terminating an Oracle sql statement with semicolon or with a slash on the next line?

The following two queries seem to be equivalent when executed in sql*plus: 1. select * from user_tables; 2. select * from user_tables / Is there any difference between both versions?
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Where to start with Oracle?

This question only needs one answer: a list of great resources for getting started with Oracle, including Database Administration, PL/SQL and SQL. You may find your question has been closed as a ...
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How to catch and handle only specific Oracle exceptions?

From this and this i guess, that there is no predefined Named System Exceptions for ORA-00955. How can I rewrite the following to catch only the error ORA-00955? begin EXECUTE IMMEDIATE ...
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Multiple operations using WITH

Is there a way to execute multiple operations using the WITH statement? Something like WITH T AS ( SELECT * FROM Tbl ) BEGIN OPEN P_OUTCURSOR FOR SELECT * FROM T; SELECT COUNT(*) INTO ...
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How to extract Procedure, Function, etc. Source Code from an Oracle Export

I have generated an EXPDAT.DMP file of an Oracle database with the command: exp userid=usr/pass@db owner=own rows=n compress=n I then ran the following command to generate a file containing the ...
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What happens when you modify (reduce) a column's length?

Lets say I have two columns of type NUMBER (without precision, and scale) and VARCHAR(300). I saw that these columns are way too large for my data, so I want to modify them to NUMBER(11) and ...
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Oracle's left join and where clauses errors

CREATE TABLE "ATABLE1" ( "COLUMN1" VARCHAR2(20 BYTE), "COLUMN2" VARCHAR2(20 BYTE) ); CREATE TABLE "ATABLE2" ( "COLUMN1" VARCHAR2(20 BYTE), "COLUMN2" VARCHAR2(20 BYTE) ); ...
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How do you protect against malicious PREPROCESSOR attacks in Oracle External Tables?

I'm a new DBA and I recently found out about the option of External Tables in Oracle using the PREPROCESSOR feature ( ...
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Multiple Oracle Instances — is this a good practice?

One of my clients has deployed our product's db into a Solaris machine which already has 3 instances of Oracle. So, right now there are 4 instances of Oracle running on the same machine. And now we're ...
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Oracle 11g: performance improvements of inserts

I have a table of 500 millions of rows (and growing) I did the following to improve performance of inserts: On database side: dropped all indexes and constraints disabled logging On application ...