General MySQL Oracle SQL Server

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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, 2852🔥, 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, 2852🔥, 0💬

Primary Key - Default Indexes of Tables in SQL Server
Is the PRIMARY KEY Column of a Table an Index in SQL Server? If you define a primary key on a table, an index for the primary key column will be created by default. The tutorial exercise below shows you the index created as part of the primary key column of "fyi_links": USE FyiCenterData; GO -- Drop... 2016-11-13, 2851🔥, 0💬

JSON_TYPE() - Detecting Type of JSON Value
How to detect the type of a JSON (JavaScript Object Notation) value using the JSON_TYPE() function? JSON_TYPE(json) is a MySQL built-in function that returns the data type of a JSON (JavaScript Object Notation) value. For example: SELECT JSON_TYPE('[]'), JSON_TYPE('{}'); -- +-----------------+------... 2025-03-12, 2850🔥, 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, 2849🔥, 0💬

Create a Single Index for Multiple Columns in Oracle
How To Create a Single Index for Multiple Columns in Oracle? If you know a group of multiple columns will be always used together as search criteria, you should create a single index for that group of columns with the "ON table_name(col1, col2, ...)" clause. Here is an example of one index for two c... 2019-04-17, 2849🔥, 0💬

Count Number of Rows with SELECT Statements in MySQL
How To Use SELECT Statement to Count Number of Rows in MySQL? If you want to count the number of rows, you can use the COUNT(*) function in the SELECT clause. The following tutorial exercise shows you some good example: mysql&gt; SELECT COUNT(*) FROM fyi_links; +----------+ | COUNT(*) | +-------... 2018-01-06, 2849🔥, 0💬

SINGLE_USER/MULTI_USER - Database User Access Options in SQL Server
How to set database to be SINGLE_USER in SQL Server? Databases in SQL Server have three user access options: MULTI_USER - All users that have the appropriate permissions to connect to the database are allowed. This is the default. SINGLE_USER - One user at a time is allowed to connect to the databas... 2016-11-20, 2849🔥, 0💬

Testing Table for SELECT Statements in SQL Server
How To Create a Testing Table with Test Data to try with SELECT statements in SQL Server? If you want to follow the tutorial exercises presented in this collection, you need to create a testing table and insert some test data, as shown in the following sample script: CREATE TABLE fyi_links (id INTEG... 2016-10-26, 2848🔥, 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, 2846🔥, 0💬

What Is Oracle Server Autotrace in Oracle
What Is Oracle Server Autotrace in Oracle? Autotrace is Oracle server feature that generates two statement execution reports very useful for performance tuning: Statement execution path - Shows you the execution loop logic of a DML statement. Statement execution statistics - Shows you various execut... 2020-06-08, 2844🔥, 0💬

Rename a Tablespace in Oracle
How To Rename a Tablespace in Oracle? You can easily rename a tablespace by using the ALTER TABLESPACE ... RENAME TO statement as shown in the example below: SQL&gt; CREATE TABLESPACE my_space 2 DATAFILE '/temp/my_space.dbf' SIZE 10M; Tablespace created. SQL&gt; ALTER TABLESPACE my_space REN... 2019-04-13, 2844🔥, 0💬

Numeric Comparison Operations in Oracle
What Are the Numeric Comparison Operations in Oracle? PL/SQL supports 6 basic numeric comparison operations as shown in the following sample script: PROCEDURE proc_comparison AS res BOOLEAN; BEGIN res := 1 = 2; res := 1 &lt; 2; res := 1 &gt; 2; res := 1 &lt;= 2; res := 1 &gt;= 2; res... 2018-08-06, 2843🔥, 0💬

Simplest Tool to Run Commands on Oracle Server in Oracle
What Is the Simplest Tool to Run Commands on Oracle Servers in Oracle? The simplest tool to connect to an Oracle server and run commands to manage data is SQL*Plus. It is an Oracle database client tool that works as a command-line user interface to the database server. SQL*Plus allows you: Format, p... 2018-06-27, 2843🔥, 0💬

Pass a Parameter to a Cursor in Oracle
How To Pass a Parameter to a Cursor in Oracle? When you define a cursor, you can set a formal parameter in the cursor. The formal parameter will be replaced by an actual parameter in the OPEN cursor statement. Here is a good example of a cursor with two parameters: CREATE OR REPLACE PROCEDURE FYI_CE... 2018-07-18, 2842🔥, 0💬

Transaction Roll Back when Session Ended in MySQL
What Happens to the Current Transaction If the Session Is Ended in MySQL? If a session is ended, the current transaction in that session will be rolled back and ended. All the database changes made in the current transaction will be removed. This is called an implicit rollback when session is ended.... 2017-08-03, 2841🔥, 0💬

What Is an External Table in Oracle
What Is an External Table in Oracle? An external table is a table defined in the database with data stored outside the database. Data of an external table is stored in files on the operating systems. Accessing data of external tables are done through data access drivers. Currently, Oracle supports t... 2016-11-27, 2841🔥, 0💬

Performing Comparison on Exact Numbers in SQL Server
How To Perform Comparison on Exact Numbers in SQL Server Transact-SQL? Comparison operations on exact numbers of data types: BIT, INT, NUMERIC, etc., are very easy to understand. Here are some simple examples: -- BIT value comparison DECLARE @x BIT, @y BIT; SET @x = 0; SET @y = 1; SELECT CASE WHEN @... 2017-01-21, 2840🔥, 0💬

Memory Usage of the MySQL Server in MySQL
How Much Memory Does the Server Take in MySQL? If you are interested to know how much memory your MySQL server is taking, you can use Windows Task Manager to find out. Try to following this tutorial exercise: Start your MySQL server. Press Ctrl-Alt-Del and click Task Manager. The Task Manager window... 2017-12-04, 2839🔥, 0💬

Viewing User Privileges in MySQL
How To View User Privileges in MySQL? If a regular user wants to see his/her own granted privileges, he/she can use the "SHOW GRANTS" command. If the "root" user wants to see other user's granted privileges, he/she can use the "SHOW GRANTS FOR userName" command. The following tutorial exercise shows... 2017-08-21, 2838🔥, 0💬

Rollback the Current Transaction in MySQL
How To Rollback the Current Transaction in MySQL? 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 command. It will remove all the database chan... 2016-10-17, 2837🔥, 0💬

Use Subqueries with the IN Operator in Oracle
How To Use Subqueries with the IN Operator in Oracle? A subquery can be used with the IN operator as "expression IN (subquery)". The subquery should return a single column with one or more rows to form a list of values to be used by the IN operation. The following tutorial exercise shows you how to ... 2019-09-27, 2836🔥, 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, 2836🔥, 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, 2836🔥, 0💬

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General MySQL Oracle SQL Server