General MySQL Oracle SQL Server

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Use NULL as Conditions in Oracle
How To Use NULL as Conditions in Oracle? If you want to compare values against NULL as conditions, you should use the "IS NULL" or "IS NOT NULL" operator. Do not use "=" or "&lt;&gt;" against NULL. The sample script below shows you some good examples: SELECT 'A' IS NULL FROM DUAL; -- Error: ... 2019-12-02, 1541🔥, 0💬

Invoke Built-in Functions in PL/SQL in Oracle
How To Invoke Built-in Functions in PL/SQL in Oracle? Of course, you can invoke SQL functions in SQL statements. But many SQL functions can also be executed in regular PL/SQL statements, as shown in the following sample script: DECLARE now DATE; id NUMBER; str VARCHAR2(40); BEGIN now := SYSDATE; DBM... 2018-09-13, 1540🔥, 0💬

Turn On and Off Recycle Bin for the Instance in Oracle
How To Turn On or Off Recycle Bin for the Instance in Oracle? You can turn on or off the recycle bin feature for an instance in the instance parameter file with "recyclebin=on/off". You can also turn on or off the recycle bin feature on the running instance with a SQL*Plus command, if you log in as ... 2019-05-14, 1538🔥, 0💬

Show Execution Path Reports in Oracle
How To Get Execution Path Reports on Query Statements in Oracle? If your user account has autotrace configured by the DBA, you can use the "SET AUTOTRACE ON EXPLAIN" command to turn on execution path reports on query statements. The tutorial exercise bellow shows you a good example: SQL&gt; CONN... 2020-06-08, 1537🔥, 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, 1537🔥, 0💬

What Is a RECORD in PL/SQL in Oracle
What Is a RECORD in PL/SQL in Oracle? RECORD is a composite data type in PL/SQL. It can have many fields representing data elements with different data types. Variables of RECORD type can be designed to hold data from database table rows. To use RECORD data type, you need to define a specific RECORD... 2018-09-13, 1535🔥, 0💬

Implicit Cursor in Oracle
What Is the Implicit Cursor in Oracle? The implicit cursor is the cursor automatically defined by PL/SQL for you. Whenever a SQL statement is executed, this cursor will be assigned to represent the execution of this statement. This implicit cursor is called SQL. It has many attributes representing s... 2018-09-13, 1535🔥, 0💬

Export Connection Information to a File in Oracle
How To Export Your Connection Information to a File in Oracle? SQL Developer allows you to export your connection information into an XML file. Here is how to do this: Right-click on Connections Select Export Connection... Enter File Name as: \temp\connections.xml Click OK Open \temp\connections.xml... 2018-10-08, 1533🔥, 0💬

Cursor Variable Easier to Use than Cursor in Oracle
Why Cursor Variables Are Easier to Use than Cursors in Oracle? Cursor variables are easier to use than cursors because: Cursor variables are easier to define. No need to give a specific query statement. Cursor variables are easier to open. You can specify the query dynamically at the time of open. C... 2018-06-27, 1533🔥, 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, 1531🔥, 0💬

Load Data from External Tables in Oracle
How To Load Data from External Tables to Regular Tables in Oracle? Once you have your data entered in a text file, and an external table defined to this text file, you can easily load data from this text file to a regular table. The following tutorial exercise shows you how to load data from the tex... 2016-10-15, 1531🔥, 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, 1530🔥, 0💬

Create Additional Tablespaces in Oracle
How To Create Additional Tablespaces for an New Database in Oracle? This is Step 8. Creating additional tablespaces can be done by using the CREATE TABLESPACE statement as shown in the following sample script: SQL&gt; CREATE TABLESPACE users 2 DATAFILE '/oraclexe/oradata/FYI/users01 .dbf'SIZE 10... 2019-03-27, 1530🔥, 0💬

Dropped Tables with Indexes in Oracle
What Happens to Indexes If You Drop a Table in Oracle? If you drop a table, what happens to its indexes? The answer is that if a table is dropped, all its indexes will be dropped too. Try the following script to see yourself: CREATE TABLE student (id NUMBER(5) PRIMARY KEY, first_name VARCHAR(80) NOT... 2019-04-22, 1529🔥, 0💬

Left Outer Join with the WHERE Clause in Oracle
How To Write a Left Outer Join with the WHERE Clause in Oracle? If you don't want to use the LEFT OUTER JOIN ... ON clause to write a left outer join, you can use a special criteria in the WHERE clause as "left_table.column = right_table.column(+)". The select statement below is an example of a left... 2019-10-18, 1527🔥, 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, 1527🔥, 0💬

Relations between a Tablespace and Data Files in Oracle
How a Tablespace Is Related to Data Files in Oracle? Each tablespace in an Oracle database consists of one or more files called datafiles, which are physical structures that conform to the operating system in which Oracle is running.   ⇒ Relation between Database and Tablespaces in Oracle ⇐ Oracle ... 2019-01-20, 1527🔥, 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, 1527🔥, 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, 1526🔥, 0💬

Systems Supported by Oracle SQL Developer in Oracle
What Operating Systems Are Supported by Oracle SQL Developer in Oracle? Oracle SQL Developer is available for three types of operating Systems: Windows Linux Mac OSX   ⇒ Download-Oracle-SQL-Developer in Oracle ⇐ What Is Oracle SQL Developer in Oracle ⇑ Introduction to Oracle SQL Developer ⇑⇑ Oracl... 2019-02-18, 1525🔥, 0💬

Export Data with Field Delimiters in Oracle
How To Export Data with a Field Delimiter in Oracle? The previous exercise allows you to export data with fixed field lengths. If you want export data with variable field lengths and field delimiters, you can concatenate your fields with an expression in the SELECT clause as shown in the tutorial ex... 2018-06-27, 1523🔥, 0💬

Omit Columns in INSERT Statements in Oracle
How To Omit Columns with Default Values in INSERT Statement in Oracle? If you don't want to specify values for columns that have default values, or you want to specify values to columns in an order different than how they are defined, you can provide a column list in the INSERT statement. If a colum... 2020-01-29, 1522🔥, 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, 1521🔥, 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, 1521🔥, 0💬

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General MySQL Oracle SQL Server