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, 2425🔥, 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, 2424🔥, 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, 2424🔥, 0💬

Use an Explicit Cursor without OPEN Statements in Oracle
How To Use an Explicit Cursor without OPEN Statements in Oracle? If you want to open a cursor and loop through its data rows in quick way, you can use the FOR ... IN ... LOOP statement in the same way as the implicit cursor. The following tutorial exercise gives you a good example: CREATE OR REPLACE... 2018-04-07, 2423🔥, 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, 2421🔥, 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, 2420🔥, 0💬

Commit the Current Transaction in Oracle
How To Commit the Current Transaction in Oracle? If you have used some DML statements updated some data objects, and you want to have the updates to be permanently recorded in the database, you can use the COMMIT statement. It will make all the database changes made in the current transaction become... 2019-09-04, 2420🔥, 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, 2418🔥, 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, 2418🔥, 0💬

Show All User Accounts in the Database in Oracle
How To Get a List of All User Accounts in the Database in Oracle? If you don't like to use a SELECT statement to get a list of all user accounts in the current database, you can use the Reports view to do this as shown in the following tutorial example. You need to connect to the server as SYSTEM to... 2019-01-26, 2413🔥, 0💬

Assign a Table Row to RECORD Variable in Oracle
How To Assign a Table Row to a RECORD Variable in Oracle? If you have a table, and want to assign a data row of that table to a RECORD variable, you need to define this RECORD variable to match the table column structure, then use the SELECT ... INTO statement to assign a data row that RECORD variab... 2018-08-14, 2413🔥, 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, 2411🔥, 0💬

Create a Table Interactively in Oracle
How To Create a Table Interactively in Oracle? If you don't want to use SQL statements to create a new table, you use SQL Developer to create one interactively. Follow the steps below to create a new table called: TIP Right-click on the Tables in the object tree area. Select Create TABLE. Create Tab... 2018-10-08, 2406🔥, 0💬

Use Group Functions in ORDER BY Clause in Oracle
Can Group Functions Be Used in the ORDER BY Clause in Oracle? If the query output is aggregated as groups, you can sort the groups by using group functions in the ORDER BY clause. The following statement returns how many employees are having the same salary in each department. The group output is so... 2019-10-27, 2405🔥, 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, 2401🔥, 0💬

Report View in SQL Developer in Oracle
What Is the Reports View in Oracle SQL Developer in Oracle? The Reports view lets you browse database information that organized by the server as special views. Information can be browsed include: Database parameters Storage information Session information Cursors Data objects User accounts Security... 2018-10-08, 2399🔥, 0💬

Use "IN" Parameters in Oracle
How To Use "IN" Parameter Properly in Oracle? Here are the rules about IN parameters: A formal IN parameter acts like constant. It can not be assigned with new values. An actual IN parameter can take a value or a variable. An actual IN parameter is passed by reference to the specified value or the v... 2018-10-19, 2398🔥, 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, 2394🔥, 0💬

Define a Variable to Match Column Data Type in Oracle
How To Define a Variable to Match a Table Column Data Type in Oracle? If you have a table, and want to define some variables to have exactly the same data types as some columns in that table, you can use table_name.column_name%TYPE as data types to define those variables. The tutorial sample below s... 2018-08-14, 2390🔥, 0💬

What Is a Procedure in Oracle
What Is a Procedure in Oracle? A procedure is a named program unit. It consists of three parts: Declaration Part - Defining the procedure name, calling parameters, local variables and local procedures. Declaration part is required. Execution Part - Defining execution logic with executable statements... 2018-01-27, 2390🔥, 0💬

What Are Group Functions in Oracle
What Are Group Functions in Oracle? Group functions are functions applied to a group of rows. Examples of group functions are: COUNT(*) - Returns the number of rows in the group. MIN(exp) - Returns the minimum value of the expression evaluated on each row of the group. MAX(exp) - Returns the maximum... 2019-12-19, 2388🔥, 0💬

Create a Table Index in Oracle
How To Create a Table Index in Oracle? If you have a table with a lots of rows, and you know that one of the columns will be used often a search criteria, you can add an index for that column to in improve the search performance. To add an index, you can use the CREATE INDEX statement as shown in th... 2019-05-01, 2386🔥, 0💬

Run Queries on External Tables in Oracle
How To Run Queries on External Tables in Oracle? If you have an external table defined as a text file with the ORACLE_LOADER driver, you can add data to the text file, and query the text file through the external table. By default, data fields in the text file should be terminated by ','. The tutori... 2016-10-15, 2381🔥, 0💬

Read Consistency in Oracle in Oracle
How Does Oracle Handle Read Consistency in Oracle? Oracle supports two options for you on how to maintain read consistency: READ WRITE (the default option), also called statement-level read consistency. READ ONLY, also called transaction-level read consistency.   ⇒ What Is a READ WRITE Transaction i... 2019-08-23, 2377🔥, 0💬

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General MySQL Oracle SQL Server