General MySQL Oracle SQL Server

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What Is a Data Lock in Oracle
What Is a Data Lock in Oracle? A data lock is logical flag the Oracle server is placed on data objects to give an exclusive right to a transaction. Statements in other transactions needs to respect data locks based on certain rules. Rules on data locks are: SELECT query statements do not create any ... 2019-08-19, 2734🔥, 0💬

Set a READ ONLY Transaction in Oracle
How To Set a Transaction To Be READ ONLY in Oracle? If you want a transaction to be set as READ ONLY, you need to the transaction with the SET TRANSACTION READ ONLY statement. Note that a DML statement will start the transaction automatically. So you have to issue the SET TRANSACTION statement befor... 2019-08-19, 2672🔥, 0💬

Restrictions in a READ ONLY Transaction in Oracle
What Are the Restrictions in a READ ONLY Transaction in Oracle? There are lots of restrictions in a READ ONLY transaction: You can not switch to READ WRITE mode. You can not run any INSERT, UPDATE, DELETE statements. You can run SELECT query statements. The tutorial exercise below shows you some of ... 2019-08-19, 2650🔥, 0💬

Supported Transaction Isolation Levels in Oracle
What Are Transaction Isolation Levels Supported by Oracle in Oracle? Oracle supports two transaction isolation levels: READ COMMITTED (the default option). If the transaction contains DML that requires row locks held by another transaction, then the DML statement waits until the row locks are releas... 2019-08-19, 2576🔥, 0💬

General Rules on Data Consistency in Oracle
What Are the General Rules on Data Consistency in Oracle? Here is a list of general rules on data consistency: All SQL statements always work with a snapshot of the database to provide data consistency. For READ WRITE transactions, the snapshot is taken when each statement starts. For READ ONLY tran... 2019-08-19, 2572🔥, 0💬

How Oracle Handles Dead Locks in Oracle
How Oracle Handles Dead Locks in Oracle? Oracle server automatically detects dead locks. When a dead lock is detected, Oracle server will select a victim transaction, and fail its statement that is blocked in the dead lock to break the dead lock. The tutorial exercise below shows you an example of s... 2019-08-08, 2738🔥, 0💬

Experiments of Data Locks in Oracle
How To Experiment a Data Lock in Oracle? If you want to have some experience with data locks, you can create two windows running two SQL*Plus sessions. In session 1, you can run a UPDATE statements to create a data lock. Before committing session 2, switch to session 2, and run a UPDATE statements o... 2019-08-08, 2618🔥, 0💬

Show Existing Locks on the Database in Oracle
How To View Existing Locks on the Database in Oracle? As can see from the pervious tutorial exercise, performance of the second session is greatly affected by the data lock created on the database. To maintain a good performance level for all sessions, you need to monitor the number of data locks on... 2019-08-08, 2606🔥, 0💬

What Is a Dead Lock in Oracle
What Is a Dead Lock in Oracle? A dead lock is phenomenon happens between two transactions with each of them holding a lock that blocks the other transaction as shown in the following diagram: (transaction 1) (transaction 2) update row X to create lock 1 update row Y to create lock 2 update row X (bl... 2019-08-08, 2453🔥, 0💬

How Data Locks Are Respected in Oracle
How Data Locks Are Respected in Oracle? Here are the rules on how data locks are respected: All statements ignore data locks owned its own transaction. SELECT query statements ignores data locks owned by any transactions. INSERT, UPDATE, and DELETE statements in a READ COMMITTED transaction will wai... 2019-08-08, 2406🔥, 0💬

AdventureWorksLT - Downloading and Installing the Sample Database in SQL Server
How to download and install the scaled-down database AdventureWorksLT in SQL Server? If you want to practice you DBA skills with the scaled-down version of the sample database AdventureWorksLT provided by Microsoft, you should follow this tutorial to download and install it first: 1. Go to the SQL S... 2019-08-04, 15548🔥, 1💬

💬 2019-08-04 Marc: many thanks

Managing Oracle User Accounts, Schema and Privileges
Where to find answers to frequently asked questions on Managing Oracle User Accounts, Schema and Privileges? Here is a list of frequently asked questions and their answers compiled by FYIcenter.com DBA team on Managing Oracle User Accounts, Schema and Privileges. Clear answers are provided with tuto... 2019-07-30, 3464🔥, 0💬

User Role: Group of Privileges in Oracle
What Is a User Role in Oracle? A user role is a group of privileges. Privileges are assigned to users through user roles. You create new roles, grant privileges to the roles, and then grant roles to users.   ⇒ System Defined User Roles in Oracle ⇐ User Account and Schema: One-to-One Relation in Ora... 2019-07-30, 3358🔥, 0💬

User Account and Schema: One-to-One Relation in Oracle
What Is the Relation of a User Account and a Schema in Oracle? User accounts and schemas have a one-to-one relation. When you create a user, you are also implicitly creating a schema for that user. A schema is a logical container for the database objects (such as tables, views, triggers, and so on) ... 2019-07-30, 3331🔥, 0💬

System Defined User Roles in Oracle
What Are the System Predefined User Roles in Oracle? Oracle 10g XE comes with 3 predefined roles: CONNECT - Enables a user to connect to the database. Grant this role to any user or application that needs database access. RESOURCE - Enables a user to create certain types of schema objects in his own... 2019-07-30, 2510🔥, 0💬

User Account and Attributes in Oracle
What Is a User Account in Oracle? A user account is identified by a user name and defines user's attributes, including the following: Password for database authentication Privileges and roles Default tablespace for database objects Default temporary tablespace for query processing work space   ⇒ Use... 2019-07-30, 2396🔥, 0💬

Built-in Internal User Accounts in Oracle
What Are Internal User Account in Oracle? An internal user account is a system predefined user account. Oracle 10g XE comes with a number of internal accounts: SYSTEM - This is the user account that you log in with to perform all administrative functions other than starting up and shutting down the ... 2019-07-21, 4067🔥, 0💬

Use SYS Account to Connect to the Server in Oracle
How To Connect to the Server with User Account: SYS in Oracle? SYS is a very special user account. It has been associated with the highest privilege call SYSDBA. Normally, you should not connect to the server with SYS. But if you want to use it, you need to use a special connect command: &gt;cd ... 2019-07-21, 3026🔥, 0💬

Use Windows User to Connect to the Server in Oracle
How To Use Windows User to Connect to the Server in Oracle? During the installation process, 10g XE will create a special Windows user group called ORA_DBA, and put your Windows user into this group. Any Windows users in this group can be connected to Oracle server with SYSDBA privilege without any ... 2019-07-21, 3007🔥, 0💬

Show All User Accounts in Oracle
How To List All User Accounts in Oracle? User accounts can be accessed through a system view called ALL_USERS. A simple SELECT statement can be used to get a list of all user accounts. Try the following script: &gt;.\bin\sqlplus /nolog SQL&gt; connect SYSTEM/fyicenter Connected. SQL&gt; ... 2019-07-21, 2828🔥, 0💬

Create a New User Account in Oracle
How To Create a New User Account in Oracle? If you want to create a new user account, you can log in as SYSTEM and use the CREATE USER command as shown in the following example: &gt;.\bin\sqlplus /nolog SQL&gt; connect SYSTEM/fyicenter Connected. SQL&gt; CREATE USER DEV IDENTIFIED BY dev... 2019-07-21, 2674🔥, 0💬

Change User Password in Oracle
How To Change User Password in Oracle? If you want to change a user's password, you can log in as SYSTEM and use the ALTER USER command as shown in the following example: &gt;.\bin\sqlplus /nolog SQL&gt; connect SYSTEM/fyicenter Connected. SQL&gt; ALTER USER DEV IDENTIFIED BY beginner; U... 2019-07-09, 2935🔥, 0💬

Delete a User Account in Oracle
How To Delete a User Account in Oracle? If you want to delete a user account and its associated schema, you can log in as SYSTEM and use the DROP USER command as shown in the following example: &gt;.\bin\sqlplus /nolog SQL&gt; connect SYSTEM/fyicenter Connected. SQL&gt; DROP USER DEV CAS... 2019-07-09, 2783🔥, 0💬

Revoke CREATE SESSION Privilege in Oracle
How To Revoke CREATE SESSION Privilege from a User in Oracle? If you take away the CREATE SESSION privilege from a user, you can use the REVOKE command as shown in the following example script: &gt;.\bin\sqlplus /nolog SQL&gt; connect SYSTEM/fyicenter SQL&gt; REVOKE CREATE SESSION FROM d... 2019-07-09, 2758🔥, 0💬

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General MySQL Oracle SQL Server