General MySQL Oracle SQL Server

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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, 2245🔥, 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, 2245🔥, 0💬

Use Group Functions in the SELECT Clause in Oracle
How To Use Group Functions in the SELECT Clause in Oracle? 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 4 values ca... 2019-11-21, 2244🔥, 0💬

Converting Integers into Date and Time Values in SQL Server
Can Integers Be Converted into Date and Time Values in SQL Server Transact-SQL? Can integers be converted into date and time values? The answer is yes. The input integer will be used as the number of days relative to the base date: Jan 1, 1900. The time of the day will be set to 0, midnight of the d... 2017-02-22, 2243🔥, 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, 2243🔥, 0💬

Use Subqueries in the FROM Clause in Oracle
How To Use Subqueries in the FROM Clause in Oracle? If you have a query returning many rows of data, and you want to perform another query on those rows, you can put the first query as a subquery in the FROM clause of the second query. The following statement shows you how to use a subquery as base ... 2019-09-27, 2242🔥, 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, 2242🔥, 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, 2241🔥, 0💬

Violation of Unique Value Constraint in MySQL
What Happens If Unique Value Constraints Are Violated in MySQL? If you are inserting a new record that has values violating a unique constraint, you will get an error. Note that primary key column has a unique value constraint by default. The following tutorial exercise gives you some good examples:... 2018-01-16, 2241🔥, 0💬

Tables Using InnoDB Storage Engine in MySQL
How To Create a New Table Using the InnoDB Storage Engine in MySQL? InnoDB storage engine was developed by Innobase Oy, which is an Oracle company now. InnoDB is transaction safe, and has been used by a number of large Websites, like Slashdot.org. InnoDB is not the default storage engine. You need t... 2017-09-01, 2241🔥, 0💬

Creating Databases with Specified Physical Files in SQL Server
How to create database with physical files specified in SQL Server? If you don't like the default behavior of the CREATE DATABASE statement, you can specify the physical database files with a longer statement: CREATE DATABASE database_name ON (NAME = logical_data_name, FILENAME = physical_data_name,... 2016-11-24, 2239🔥, 0💬

What Is "mysqlshow" Command in MySQL
What Is "mysqlshow" in MySQL? "mysqlshow" is a command-line interface for end users to see information on tables and columns. Here are some sample commands supported by "mysqlshow": "mysqlshow" - Shows all the databases. "mysqlshow databaseName" - Shows all the tables in the specified database. "mys... 2018-02-28, 2238🔥, 0💬

JSON_STORAGE_SIZE() - Storage Size of JSON Value
How to calculate the storage size of a JSON (JavaScript Object Notation) value using the JSON_STORAGE_SIZE() function? JSON_STORAGE_SIZE(json) is a MySQL built-in function that calculates the storage size of a JSON (JavaScript Object Notation) value or table column. For example: SELECT JSON_STORAGE_... 2025-03-12, 2237🔥, 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, 2237🔥, 0💬

What Is Index in MySQL
What Is Index in MySQL? An index is a single column or multiple columns defined to have values pre-sorted to speed up data retrieval speed.   ⇒ What Is View in MySQL ⇐ What Is Foreign Key in MySQL ⇑ Database Basics and Terminologies in MySQL ⇑⇑ MySQL Database Tutorials 2017-07-07, 2236🔥, 0💬

Insert a RECORD into a Table in Oracle
How To Insert a RECORD into a Table in Oracle? If you have a RECORD variable with data fields matching a table structure, you can insert a row to this table with this RECORD variable using the INSERT statement as shown in the example below: CREATE TABLE emp_temp AS SELECT * FROM employees; CREATE OR... 2018-08-14, 2235🔥, 0💬

Retrieve Data from an Explicit Cursor in Oracle
How To Retrieve Data from an Explicit Cursor in Oracle? If you have a cursor opened ready to use, you can use the FETCH ... INTO statement to retrieve data from the cursor into variables. FETCH statement will: Retrieve all the fields from the row pointed by the current cursor pointer and assign them... 2018-07-22, 2235🔥, 0💬

Giving Privileges at Server Level in MySQL
How To Grant User Privileges at the Global Level in MySQL? If you want to grant a user privilege at the global level, you can use the "GRANT privilegeName ON *.* TO userName" command. The argument "*.*" in the command stands for all database and all tables. The following tutorial exercise shows you ... 2017-08-21, 2235🔥, 0💬

What Is Primary key in MySQL
What Is Primary Key in MySQL? A primary key is a single column or multiple columns defined to have unique values that can be used as row identifications.   ⇒ What Is Foreign Key in MySQL ⇐ What Is Row in MySQL ⇑ Database Basics and Terminologies in MySQL ⇑⇑ MySQL Database Tutorials 2017-07-07, 2235🔥, 0💬

"INSERT INTO" - Inserting a New Row into a Table in SQL Server
How To Insert a New Row into a Table with "INSERT INTO" Statements in SQL Server? To insert a new row into a table, you can use the INSERT INTO statement with values specified for all columns as in the following syntax: INSERT INTO table_name VALUES (list_of_values_of_all columns) Note that the list... 2016-11-03, 2235🔥, 0💬

Deleting All Rows with TRUNCATE TABLE Statement in SQL Server
How To Delete All Rows with TRUNCATE TABLE Statement in SQL Server? If you want to delete all rows from a table, you have two options: Use the DELETE statement with no WHERE clause. Use the TRUNCATE TABLE statement. The TRUNCATE statement is more efficient the DELETE statement. The tutorial exercise... 2016-10-30, 2235🔥, 0💬

Create a New Table by Selecting Rows from Another Table in Oracle
How To Create a New Table by Selecting Rows from Another Table in Oracle? Let's say you have a table with many data rows, now you want to create a backup copy of this table of all rows or a subset of them, you can use the CREATE TABLE...AS SELECT statement to do this. Here is an example script: &... 2019-06-01, 2234🔥, 0💬

Character String Data Types in MySQL
What Are Character String Data Types in MySQL? MySQL supports the following string data types: CHAR(n) same as CHARACTER(n) - Fixed width and " " padded characters strings. Default character set is ASCII. NCHAR(n) same as NATIONAL CHARACTER(n) - Fixed width and " " padded character strings with UTF8... 2018-04-12, 2233🔥, 0💬

Select All Columns of All Rows in Oracle
How To Select All Columns of All Rows from a Table in Oracle? The simplest query statement is the one that selects all columns of all rows from a table: "SELECT * FROM table_name;". The (*) in the SELECT clause tells the query to return all columns. The tutorial exercise below gives you a good examp... 2019-12-19, 2230🔥, 0💬

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General MySQL Oracle SQL Server