General MySQL Oracle SQL Server

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Lock and Unlock a User Account in Oracle
How To Lock and Unlock a User Account in Oracle? If you want to lock a user account for a short period of time, and unlock it later, you can use the ALTER USER ... ACCOUNT command. The following sample script shows how to use this command: &gt;.\bin\sqlplus /nolog SQL&gt; connect SYSTEM/fyic... 2019-06-29, 2418🔥, 0💬

Evaluating Expressions with SELECT Statements in MySQL
How To Calculate Expressions with SELECT Statements in MySQL? There is no special SQL statements to calculate expressions. But you can use the "SELECT expression FROM DUAL" statement return the calculated value of an expression. "DUAL" is a dummy table in the server. The tutorial exercise below show... 2018-04-12, 2418🔥, 0💬

Use Existing Column Values in the SET Clause in MySQL
How To Use Existing Column Values in the SET Clause in MySQL? If a row matches the WHERE clause in a UPDATE statement, existing values in this row can be used in expressions to provide new values in the SET clause. Existing values are represented by column names in the expressions. The tutorial exer... 2018-01-13, 2418🔥, 0💬

DROP TABLE Statement in Oracle
How To Drop an Existing Table in Oracle? If you want to delete an existing table and its data rows, you can use the DROP TABLE statement as shown in this script: SQL&gt; connect HR/fyicenter Connected. SQL&gt; CREATE TABLE emp_dept_10 2 AS SELECT * FROM employees WHERE department_id=10; Tabl... 2020-02-20, 2416🔥, 0💬

What Is a SELECT Query Statement in Oracle
What Is a SELECT Query Statement in Oracle? The SELECT statement is also called the query statement. It is the most frequently used SQL statement in any database application. A SELECT statement allows you to retrieve data from one or more tables, or views, with different selection criteria, grouping... 2020-01-04, 2416🔥, 0💬

What Is NULL Value in MySQL
What Are NULL Values in MySQL? NULL is a special value that represents no value. Here are basic rules about NULL values: NULL presents no value. NULL is not the same as an empty string ''. NULL is not the same as a zero value 0. NULL can be used as any data type. NULL should not be used in any compa... 2018-03-28, 2416🔥, 0💬

Restrictions on External Table Columns in Oracle
What Are the Restrictions on External Table Columns in Oracle? When creating external table columns, you need to watch out some restrictions: "PRIMARY KEY" is not allowed. "NOT NULL" is not allowed. "DEFAULT value" is not allowed.   ⇒ What Is a Directory Object in Oracle ⇐ Load Data through Externa... 2016-11-27, 2416🔥, 0💬

ALTER VIEW - Modifying Existing Views in SQL Server
How To Modify the Underlying Query of an Existing View in SQL Server? If you have an existing view, and want to change the underlying SELECT statement, you can use the "ALTER VIEW ..." statement to redefine the view. The tutorial exercise below shows you how modify an existing view: USE FyiCenterDat... 2016-11-04, 2416🔥, 0💬

What Is a Transaction in Oracle
What Is a Transaction in Oracle? A transaction is a logical unit of work requested by a user to be applied to the database objects. Oracle server introduces the transaction concept to allow users to group one or more SQL statements into a single transaction, so that the effects of all the SQL statem... 2019-09-16, 2414🔥, 0💬

Run SQL Statements with SQL Developer in Oracle
How To Run SQL Statements with Oracle SQL Developer in Oracle? Once a connection is established with an Oracle server, you can enter any SQL statements in the SQL Statement area. Try yourself with the following steps: Go to the SQL Statement area Enter SELECT username, default_tablespace FROM USER_U... 2018-10-08, 2414🔥, 0💬

What Are Stored Procedures in SQL Server
What Are Stored Procedures in SQL Server Transact-SQL? A stored procedure is a collection of Transact-SQL statements that stored in the SQL Server. A stored procedure can be executed later with an EXEC statement. SQL Server supports stored procedures with the following features: 1. Stored procedures... 2017-01-11, 2414🔥, 0💬

Using Group Functions in the SELECT Clause in MySQL
How To Use Group Functions in the SELECT Clause in MySQL? If group functions are used in the SELECT clause, they will be used on the rows that meet the query selection criteria, the output of group functions will be returned as output of the query. The following select statement returns 3 values cal... 2018-01-06, 2412🔥, 0💬

Selecting an Existing Database in MySQL
How To Select an Exiting Database in MySQL? The first thing after you have created a connection object to the MySQL server is to select the database where your tables are located, by using the mysql_select_db() function. If your MySQL server is offered by your Web hosting company, they will assign a... 2017-10-23, 2410🔥, 0💬

Show All Indexes of a given Table in MySQL
How To Get a List of Indexes of a Given Table in MySQL? If you want to see the index you have just created for an existing table, you can use the "SHOW INDEX FROM tableName" command to get a list of all indexes in a given table. The tutorial script below shows you a nice example: mysql&gt; SHOW ... 2018-02-14, 2409🔥, 0💬

Sorting Query Output in MySQL
How To Sort the Query Output in MySQL? If you want the returning rows to be sorted, you can specify a sorting expression in the ORDER BY clause. The simplest sort expression is column name who's values will be sorted by. The following select statement returns rows sorted by the values in the "counts... 2017-11-02, 2409🔥, 0💬

Date-Only DATETIME Values in SQL Server Transact-SQL
What Happens If Date-Only Values Are Provided for DATETIME in SQL Server Transact-SQL? If only date value is provided in a DATETIME variable, the SQL Server will pad the time value with a zero, or '00:00:00.000', representing the midnight time of the day. The tutorial exercise below gives you some g... 2017-04-08, 2409🔥, 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, 2408🔥, 0💬

Adding a New User Account in MySQL
How To Add a New User Account in MySQL? If you want to add a new user account, you can connect to the server as "root" and use the "CREATE USER ..." command. The command syntax for create a new user account with a specified user name and password is: CREATE USER userName IDENTIFIED BY 'passwordStrin... 2017-09-08, 2408🔥, 0💬

Deleting an Existing Database in MySQL
How To Drop an Existing Database in MySQL? If want to drop an existing database from the MySQL server, you can use the DROP DATABASE statement. Here is a good example of dropping an existing database: $con = mysql_connect('localhost:8888' ,'dev', 'iyf'); $sql = 'DROP DATABASE fyi'; if (mysql_query($... 2017-10-23, 2407🔥, 0💬

Rollback the Current Transaction in Oracle
How To Rollback the Current Transaction in Oracle? If you have used some DML statements updated some data objects, you find a problem with those updates, and you don't want those updates to be permanently recorded in the database, you can use the ROLLBACK statement. It will remove all the database c... 2019-09-04, 2406🔥, 0💬

Recover a Dropped Table in Oracle
How To Recover a Dropped Table in Oracle? If you accidentally dropped a table, can you recover it back? The answer is yes, if you have the recycle bin feature turned on. You can use the FLASHBACK TABLE ... TO BEFORE DROP statement to recover a dropped table from the recycle bin as shown in the follo... 2019-05-14, 2406🔥, 0💬

Convert Character Types to Numeric Types in Oracle
How To Convert Character Types to Numeric Types in Oracle? You can convert character types to numeric types in two ways: Explicitly by using TO_NUMBER() function. Implicitly by putting character data in a numeric operation. The sample script below shows you how to convert character types to numeric ... 2018-11-17, 2406🔥, 0💬

Use DML Statements in PL/SQL in Oracle
Can DML Statements Be Used in PL/SQL in Oracle? Yes, you can run almost any DML statements in PL/SQL directly. To manipulate Oracle database data you can include INSERT, UPDATE, and DELETE statements, directly in PL/SQL programs, without any special notation, as shown in the following sample code: (... 2018-10-13, 2406🔥, 0💬

Database Basics and Terminologies in MySQL
Where to find answers to frequently asked questions on Database Basics and Terminologies in MySQL? Here is a list of frequently asked questions and their answers compiled by FYIcenter.com DBA team on Database Basics and Terminologies in MySQL to help you review your knowledge. A short answer is prov... 2017-07-21, 2406🔥, 0💬

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General MySQL Oracle SQL Server