General MySQL Oracle SQL Server

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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, 2297🔥, 0💬

Drop an Existing Index in Oracle
How To Drop an Existing Index in Oracle? If you don't need an existing index any more, you should delete it with the DROP INDEX statement. Here is an example SQL script: CREATE TABLE student (id NUMBER(5) PRIMARY KEY, first_name VARCHAR(80) NOT NULL, last_name VARCHAR(80) NOT NULL, birth_date DATE N... 2020-02-20, 2296🔥, 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, 2294🔥, 0💬

Create an Oracle Database Manually in Oracle
How To Create an Oracle Database Manually in Oracle? Based on Oracle's Administrator Guide, there are 11 steps to create a database with the CREATE DATABASE statement: Step 1: Decide on Your Instance Identifier (SID) Step 2: Establish the Database Administrator Authentication Method Step 3: Create t... 2019-04-03, 2293🔥, 0💬

Drop an Existing View in Oracle
How To Drop an Existing View in Oracle? If you have an existing view, and you don't want it anymore, you can delete it by using the DROP VIEW statement as shown in the following script: DROP VIEW employee_department; View dropped.   ⇒ Understanding SQL DML Statements for Oracle ⇐ Create a New View ... 2020-02-07, 2292🔥, 0💬

Query with a Right Outer Join in Oracle
How To Write a Query with a Right Outer Join in Oracle? If you want to query from two tables with a right outer join, you can use the RIGHT OUTER JOIN ... ON clause in the FROM clause. The following query returns output with a right outer join from two tables: departments and employees. The join con... 2019-10-18, 2290🔥, 0💬

Create a Stored Procedure Interactively in Oracle
How To Create a Procedure Interactively in Oracle? If you want to create a stored procedure interactively, you can use the following steps: Open you connection name, like Local_XE. Right-click Procedures. Select Create PROCEDURE. The Create Procedure window shows up. Enter Name as: Hello Click OK. T... 2019-01-12, 2288🔥, 0💬

Sort Query Output in Descending Order in Oracle
How To Sort Query Output in Descending Order in Oracle? If you want to sort a column in descending order, you can specify the DESC keyword in the ORDER BY clause. The following SELECT statement first sorts the department in descending order, then sorts the salary in ascending order: SQL&gt; SELE... 2019-12-19, 2287🔥, 0💬

Loop through a Cursor Variable in Oracle
How To Loop through a Cursor Variable in Oracle? Once a cursor variable is opened with a query statement, it will have the same attributes as a normal cursor and it can be used in the same way a normal cursor too. The following sample script shows you how to loop through a cursor variable: CREATE OR... 2018-07-18, 2285🔥, 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, 2284🔥, 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, 2283🔥, 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, 2283🔥, 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, 2283🔥, 0💬

Execute a Simple Stored Procedure in Oracle
How To Execute a Stored Program Unit in Oracle? If you want to execute a stored program unit, you can use the EXECUTE statement. The example script below shows how to executes a stored program unit: SQL&gt; set serveroutput on; SQL&gt; CREATE PROCEDURE Hello AS 2 BEGIN 3 DBMS_OUTPUT.PUT_LINE... 2019-03-20, 2281🔥, 0💬

Define a Data Field as NOT NULL in Oracle
How To Define a Data Field as NOT NULL in Oracle? When defining a specific RECORD type, you can define a data field as NOT NULL to make sure variables with this RECORD type to always have values in this field. A field defined as NOT NULL must have a default value. Here is a tutorial script showing y... 2018-09-01, 2280🔥, 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, 2279🔥, 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, 2275🔥, 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, 2274🔥, 0💬

Add Another Datafile to a Tablespace in Oracle
How To Add Another Datafile to a Tablespace in Oracle? If you created a tablespace with a data file a month ago, now 80% of the data file is used, you should add another data file to the tablespace. This can be done by using the ALTER TABLESPACE ... ADD DATAFILE statement. See the following sample s... 2019-04-09, 2273🔥, 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, 2272🔥, 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, 2272🔥, 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, 2271🔥, 0💬

Ways to Join Two Tables in a Single Query in Oracle
How To Join Two Tables in a Single Query in Oracle? Two tables can be joined together in a query in 4 ways: Inner Join: Returns only rows from both tables that satisfy the join condition. Left Outer Join: Returns rows from both tables that satisfy the join condition, and the rest of rows from the fi... 2019-10-27, 2268🔥, 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, 2265🔥, 0💬

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General MySQL Oracle SQL Server