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40
votes
4answers
363k views

How to use sqlplus to connect to an Oracle Database located on another host without modifying my own tnsnames.ora

I want to connect to an oracle database located on another host using sqlplus. This page suggested adding an item on my tnsnames to conenct to that database local_SID = (DESCRIPTION = (ADDRESS ...
36
votes
5answers
25k views

Why not use a table instead of a materialized view?

I'm new to Oracle databases. If I have understood correctly, materialized view is a view which result set is saved as a physical table in the database and this view/table is refreshed bases on some ...
34
votes
5answers
82k views

Difference between database vs user vs schema

I'm really confused with the terms database, user and schema. Can anyone explain how they are different from each other (if they are)? If they are same then, what are the similarities between them? ...
28
votes
13answers
77k views

Eliminate duplicates in ListAgg (Oracle)

Prior to Oracle 11.2 I was using a custom aggregate function to concatenate a column into a row. 11.2 Added the LISTAGG function, so I am trying to use that instead. My problem is that I need to ...
26
votes
3answers
43k views

What is the difference between sys and system accounts in Oracle databases?

There are two ways to connect to Oracle as a administrator using sqlplus: sqlplus sys as sysdba sqlplus system/manager These accounts should be uses for different purposes, I suppose. Which tasks ...
25
votes
4answers
12k views

Why is OS authentication considered poor security for Oracle databases?

Oracle is deprecating OS authentication according to the Oracle Database Security Guide, which says Be aware that the REMOTE_OS_AUTHENT parameter was deprecated in Oracle Database 11g Release ...
24
votes
2answers
3k views

As a DBA, how would I go about transitioning from Oracle to SQL Server?

I'm an Oracle DBA that also has Sybase experience. What are the major architectural and conceptual differences between the two RDBMS platforms? An answer similar to the SQl Server->Oracle question ...
24
votes
2answers
5k views

How to make a transition from SQL Server DBA to Oracle?

As an interest, if I would to transition from a SQL Server DBA to Oracle what will be the major learning or unlearning that I would have to do? I would assume the concepts are the same and the ...
23
votes
5answers
113k views

How to select the first row of each group?

I have a table like this: ID | Val | Kind ---------------------- 1 | 1337 | 2 2 | 1337 | 1 3 | 3 | 4 4 | 3 | 4 I want to make a SELECT that will return just the ...
21
votes
9answers
34k views

How does the Oracle DUAL table work?

SQL> desc dual Name Null? Type ----------------------------------------- -------- ---------------------------- DUMMY ...
21
votes
8answers
20k views

How do you version your Oracle database changes?

I am interested to know what methods other people are using to keep track of changes made to the database including table definition changes, new objects, packages changes, etc. Do you use flat files ...
20
votes
7answers
18k views

Oracle - Any way to view uncommited changes to a particular table?

I'm debugging through a batch process currently that does a lot of DML statements, but doesn't do a commit right away. It would be nice to be able to view the "pending" changes from another session ...
19
votes
5answers
102k views

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 ...
19
votes
7answers
95k views

Import a Oracle DMP file into a Fresh install of oracle

A client sent us an Oracle database we need to test against. We don't use Oracle or have any in-house Oracle expertise. We need to setup the database so we can connect to it and debug a problem. I ...
18
votes
2answers
3k views

Difference between GROUP BY B,A and GROUP BY COALESCE(B,A)

I have been getting myself very confused. Could somebody kindly explain under what circumstances I would want to use a GROUP BY COALESCE? My guess is that I would use it if I wanted to conditionally ...
17
votes
13answers
5k views

Comfortable sqlplus interface?

I found sqlplus'interface is rather outdated. It's quite nice to have some commands or keywords at disposal, but for example no "arrow-up" key for the previous history entry is available. What is a ...
17
votes
5answers
177k 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. ...
17
votes
2answers
113k views

oracle - list users with access to certain tables

I'm sure this has been asked before but I can't seem to find the relevant details for the following. Is there some sort of pre-built table that can do the following (I have used dba_tab_privs but it ...
17
votes
4answers
2k views

SSDs with Oracle

We've been looking into using SSDs with Oracle to speed up our test migration runs. It currently takes 12-18 hours to complete a migration run, depnding on the volume of data (we're obviously doing ...
16
votes
3answers
19k views

What is the difference between Oracle's VARCHAR and VARCHAR2 datatypes?

When migrating tables coming from other DBMSs to Oracle, one of the standard tasks is to replace all VARCHAR(n) fields with VARCHAR2(n) fields (provided n <= 4000). Why does Oracle call this ...
16
votes
7answers
144k views

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 ...
16
votes
6answers
15k views

Oracle Creating ER Diagrams and Data Dictionaries

I am new to Oracle Databases and would like to develop a data dictionary and ER Diagrams for our existing databases. Do you have any tips, scripts, tools for doing so?
16
votes
6answers
45k views

Best way to delete very large recordset in Oracle

I manage an application which has a very large (nearly 1TB of data with more than 500 million rows in one table) Oracle database back end. The database doesn't really do anything (no SProcs, no ...
16
votes
3answers
43k views

Can I change the SID of an Oracle database?

The Server is Oracle Database 11g Enterprise Edition Release 11.1.0.7.0 - 64bit Is there an easy & quick way to change the SIDs of the test databases on the server? Dropping & recreating of ...
16
votes
2answers
4k views

Index vs. partition

Why is it not possible to achieve performance improvements with indexes only, so that other techniques like table partitioning becomes necessary? The question relates only to performance, of course ...
16
votes
2answers
86k views

Oracle: Quick way to list all database links

The title says it all, is there a way to quickly list all the current database links in oracle? Something along the same lines as this, which lists the current user's tables: select * from ...
16
votes
4answers
57k 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.
15
votes
6answers
28k views

What is the recommended RAID configuration for an Oracle database?

RAID (Redundant Arrays of Inexpensive Disks) comes with different configurations (RAID-0, RAID-1...). What is the recommended RAID configuration that I should set up and use when installing an Oracle ...
15
votes
4answers
11k views

How to differentiate between SQL and PL/SQL?

I know the question might sound too stupid, but I never understood this part. SQL*Plus works with both SQL and PL/SQL. How do I know whether some code is SQL or PL/SQL? If my code has a for ...
14
votes
2answers
13k views

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 ...
14
votes
3answers
2k views

Is there any point in undersizing VARCHAR columns?

Googling around there seems to be mixed reports whether the size of a VARCHAR2 column in Oracle impacts performance or not. I would like to give the question of VARCHAR size a little twist and hope ...
14
votes
4answers
5k 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 ...
14
votes
2answers
23k views

Is commit necessary after DML operation in Function/Procedure?

I wonder to know if it is necessary to write commit after insert/delete/update in function/procedure? Example: create or replace function test_fun return number is begin delete from a; return ...
14
votes
3answers
1k views

Oracle is not using a unique index for a long key

I have a table with 250K rows in my test database. (There are a few hundred millions in production, we can observe the same issue there.) The table has an nvarchar2(50) string identifier, not null, ...
14
votes
4answers
128k views

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 ...
14
votes
1answer
311 views

Term for a one-row table?

Is there a specific term to describe a relation with a cardinality of one? I'm thinking particularly of RDBMS "special" one-row tables, for example, DUAL (Oracle), SYSIBM.SYSDUMMY1 (DB2, Derby) and ...
14
votes
8answers
19k views

Tools to monitor Oracle Database Performance on Standard Edition

Here is what I am looking for: Works on Standard Edition i.e. No Diagnostic Pack. Provides both current and historical performance data. Good visuals for easy spotting of trends and presentation ...
13
votes
5answers
2k views

What features of Oracle make it an attractive choice for small projects?

Given Oracle's licensing handling[a] (and, to a lesser extent, cost) I have always been wondering what the deciding factors would be for choosing Oracle over PostgreSQL or MySQL. My company is nearly ...
13
votes
3answers
35k views

Pivot rows into multiple columns

I have a SQL Server instance that has a linked server to an Oracle server. There is a table on the Oracle server called PersonOptions which contains the following data: ╔══════════╦══════════╗ ║ ...
13
votes
2answers
89k views

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 ...
13
votes
2answers
1k views

Peculiar Oracle outer join syntax case

I have seen the following in a query that was supposed to be ported from Oracle outer join syntax to SQL standard outer join syntax: SELECT ... FROM A, B, C, D, E WHERE A.A_ID = B.A_ID AND B.B_ID = ...
13
votes
2answers
1k views

forensically deleting/updating data

I have a need to forensically remove data from oracle. If I just delete it, my understanding is the data will still actually be in the data file until that space is reused. I'm not concerned about the ...
12
votes
4answers
2k views

Reason to not use nullable number in Oracle?

Our company is interfacing with another software company for a joint project, and we were told that, if a particular value should not be displayed, we should pass in a -5000 (their arbitrary sentinel ...
12
votes
3answers
6k views

How do indices impact query performance?

Obviously keeping several different indices has a negative impact on insert and delete performance. How about query performance: Does it make sense at all keeping too many indices on a table? Will the ...
12
votes
1answer
82k views

How to transfer data using expdp and impdp commands?

I'm Oracle noob, and my intention is to transfer all data and metadata from one schema to another schema within an Oracle database. I'm planning to use datapump expdp and impdp commands. I have ...
12
votes
2answers
75k views

How do you show SQL executing on an Oracle database?

How can you show the SQL that is currently executing on an oracle db? Extra information that would be useful would include user, session id etc.
12
votes
1answer
55k views

How do I declare and use variables in Oracle?

My main skills are with SQL Server, but I have been asked to do some tuning of an Oracle query. I have written the following SQL: declare @startDate int select @startDate = 20110501 And I get this ...
12
votes
2answers
534 views

Are there any benefits in certain ordering of columns when defining indexes

For example, if I have two indexes: CREATE INDEX IDX_1 ON MY_TABLE_1 (ITEM, DATE, LOCATION) COMPUTE STATISTICS; CREATE INDEX IDX_2 ON MY_TABLE_1 (DATE, LOCATION, ITEM) COMPUTE STATISTICS; ...
12
votes
1answer
10k views

What are the benefits of packages over standalone procedures and functions?

Looking for a canonical answer to the question of why packages should be preferred in an Oracle database over stand alone procedures and functions.
12
votes
2answers
3k views

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 ...