W3schools sql

SQL is a standard language for storing, manipulating and retrieving data in databases. Our SQL tutorial will teach you how to use SQL in: MySQL, SQL Server, MS Access, Oracle, Sybase, Informix, Postgres, and other database systems. Examples in Each Chapter With our online SQL editor, you can edit the SQL statements, and click on a button to view the result. SPONSORED CONTENT SQL Examples Learn by examples! This tutorial supplements all explanations with clarifying examples. SQL Quiz Test Test your SQL skills at W3Schools! My Learning Track your progress with the free "My Learning" program here at W3Schools. Log in to your account, and start earning points! This is an optional feature. You can study W3Schools without using My Learning. SQL References At W3Schools you will find a complete reference for keywords and function: SQL Data Types Data types and ranges for Microsoft Access, MySQL and SQL Server. W3Schools is optimized for learning and training. Examples might be simplified to improve reading and learning. Tutorials, references, and examples are constantly reviewed to avoid errors, but we cannot warrant full correctness of all content. While using W3Schools, you agree to have read and accepted our

Summary: in this tutorial, you will learn how to use the SQL Server cursor to process a result set, one row at a time. SQL works based on set e.g., What is a database cursor A database cursor is an object that enables traversal over the rows of a result set. It allows you to process individual row returned by a query. SQL Server cursor life cycle These are steps for using a cursor: First, declare a cursor. DECLARE cursor_name CURSOR FOR select_statement; Code language: SQL (Structured Query Language) ( sql ) To declare a cursor, you specify its name after the DECLARE keyword with the CURSOR data type and provide a Next, open and populate the cursor by executing the SELECT statement: OPEN cursor_name; Code language: SQL (Structured Query Language) ( sql ) Then, fetch a row from the cursor into one or more FETCH NEXT FROM cursor INTO variable_list; Code language: SQL (Structured Query Language) ( sql ) SQL Server provides the @@FETCHSTATUS function that returns the status of the last cursor FETCH statement executed against the cursor; If @@FETCHSTATUS returns 0, meaning the FETCH statement was successful. You can use the WHILE @@FETCH_STATUS = 0 BEGIN FETCH NEXT FROM cursor_name; END; Code language: SQL (Structured Query Language) ( sql ) After that, close the cursor: CLOSE cursor_name; Code language: SQL (Structured Query Language) ( sql ) Finally, deallocate the cursor: DEALLOCATE cursor_name; Code language: SQL (Structured Query Language) ( sql ) SQL Server cursor example...

ROW_NUMBER() OVER ( [PARTITION BY expr1, expr2,...] ORDER BY expr1 [ASC | DESC], expr2,... ) Code language: SQL (Structured Query Language) ( sql ) In this syntax, • First, the PARTITION BY clause divides the result set returned from the FROMclauseinto partitions. The PARTITION BY clause is optional. If you omit it, the whole result set is treated as a single partition. • Then, the ORDER BY clause sorts the rows in each partition. Because the ROW_NUMBER() is an order sensitive function, the ORDER BY clause is required. • Finally, each row in each partition is assigned a sequential integer number called a row number. The row number is reset whenever the partition boundary is crossed. SQL ROW_NUMBER()examples We will use the employees and departments tables from the A) Simple SQL ROW_NUMBER() example The following statement finds the first name, last name, and salary of all employees. In addition, it uses the ROW_NUMBER() function to add sequential integer number to each row. SELECT ROW_NUMBER() OVER ( ORDER BY salary ) row_num, first_name, last_name, salary FROM employees; Code language: SQL (Structured Query Language) ( sql ) The following picture shows the partial result set: B) Using SQL ROW_NUMBER() for pagination The ROW_NUMBER() function can be used for pagination. For example, if you want to display all employees on a table in an application by pages, which each page has ten records. • First, use the ROW_NUMBER() function to assign each row a sequential integer numbe...

report this ad report this ad Database normalization is a database schema design technique, by which an existing schema is modified to minimize redundancy and dependency of data. Normalization split a large table into smaller tables and define relationships between them to increases the clarity in organizing data. Some Facts About Database Normalization • The words normalization and normal form refer to the structure of a database. • Normalization was developed by IBM researcher E.F. Codd In the 1970s. • Normalization increases clarity in organizing data in Databases. Normalization of a Database is achieved by following a set of rules called 'forms' in creating the database. Database Normalization Rules • • • • • • First Normal Form (1NF) Each column is unique in 1NF. Example: Sample Employee table, it displays employees are working with multiple departments. Employee Age Department Melvin 32 Marketing, Sales Edward 45 Quality Assurance Alex 36 Human Resource Employee table following 1NF: Employee Age Department Melvin 32 Marketing Melvin 32 Sales Edward 45 Quality Assurance Alex 36 Human Resource Second Normal Form (2NF) The entity should be considered already in 1NF, and all attributes within the entity should depend solely on the unique identifier of the entity. Example: Sample Products table: productID product Brand 1 Monitor Apple 2 Monitor Samsung 3 Scanner HP 4 Head phone JBL Product table following 2NF: Products Category table: productID product 1 Monitor 2 Scanner...

Introduction Welcome to the PostgreSQL Tutorial. This tutorial is designed to give details to PostgreSQL, relational database concepts, and the SQL language. We only assume some general knowledge on PostgreSQL is claimed to be the most advanced open source database solution. PostgreSQL is an object-relational database management system (ORDBMS). PostgreSQL is pronounced Post-Gres-Q-L. PostgreSQL development is performed by a team of mostly volunteer developers spread throughout the world and communicating via the Internet. It is a community project and is not controlled by any company. The "PGDG" is an international, unincorporated association of individuals and companies who have contributed to the PostgreSQL project. The PostgreSQL PostgreSQL is distributed under a license similar to BSD and MIT. Basically, it allows users to do anything they want with the code, including reselling binaries without the source code. The only restriction is that you not hold them legally liable for problems with the software. There is also the requirement that this History of PostgreSQL In 1986 the Defense Advanced Research Projects Agency (DARPA), the Army Research Office (ARO), the National Science Foundation (NSF), and ESL, Inc sponsored Berkeley POSTGRES Project which was led by Michael Stonebraker. In 1987 the first demo version of the project is released. In June 1989, Version 1 was released to some external users. Version 2 and 3 were released in 1990 and 1991. Version 3 had support...

report this ad report this ad SQL (Structured Query Language) commands are instructions to communicate with a relational database management system (RDBMS) to perform various tasks such as data manipulation, data definition, and data control. These commands allow users to perform specific operations on the database, such as creating, altering, and deleting tables, inserting, updating, and retrieving data, setting user permissions, etc. This tutorial will cover some of the most commonly used SQL commands. SQL Commands SQL Command Description The CREATE DATABASE command is used to create a new database. The CREATE TABLE command is used to create a new table in the database. ALTER DATABASE The ALTER DATABASE command is used to modify the structure of a database. ALTER TABLE The ALTER TABLE command is used to modify the structure of a table. DROP TABLE The DROP TABLE command is used to delete a table. SELECT The SELECT command is used to retrieve data from a database. UPDATE The UPDATE command is used to modify existing records in a table. DELETE The DELETE command is used to delete records from a table. INSERT INTO The INSERT command is used to add new records to a table. These are just a few examples of the many SQL commands available. Please note that SQL commands are executed in a specific order; First, create a database, then create a table, then you can insert, update, delete or select data from it. Print Page

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