SQL Self JOIN
SQL Self JOIN A self JOIN is a regular join, but the table is joined with itself. Self JOIN Syntax SELECT column_name(s) FROM table1 T1, table1 T2 WHERE condition; Demo Database In this tutorial we will use the well-known Northwind sample database. Below is a selection from the "Customers" table:
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SQL UNIQUE Constraint
SQL UNIQUE Constraint The UNIQUE constraint ensures that all values in a column are different. Both the UNIQUE and PRIMARY KEY constraints provide a guarantee for uniqueness for a column or set of columns. A PRIMARY KEY constraint automatically has a UNIQUE constraint. However, you can have many UNIQUE constraints per table, but only one PRIMARY KEY constraint per table.
SQL NOT NULL Constraint
SQL NOT NULL Constraint By default, a column can hold NULL values. The NOT NULL constraint enforces a column to NOT accept NULL values. This enforces a field to always contain a value, which means that you cannot insert a new record, or update a record without adding a value to this field. SQL NOT NULL on CREATE TABLE The following SQL ensures that the "ID", "LastName", and "FirstName" columns will NOT accept NULL values when the "Persons" table is created: SQL NOT NULL on ALTER TABLE To create a NOT NULL constraint on the "Age" column when the "Persons" table is already created, use the following SQL: ALTER TABLE Persons MODIFY Age int NOT NULL;
SQL FULL OUTER JOIN Keyword
SQL FULL OUTER JOIN Keyword The FULL OUTER JOIN keyword return all records when there is a match in left (table1) or right (table2) table records. Note: FULL OUTER JOIN can potentially return very large result-sets! Tip: FULL OUTER JOIN and FULL JOIN are the same. FULL OUTER JOIN Syntax SELECT column_name(s) FROM table1 FULL OUTER JOIN table2 ON table1.column_name = table2.column_name WHERE condition;
SQL IFNULL(), ISNULL(), COALESCE(), and NVL() Functions
SQL IFNULL(),ISNULL(), COALESCE(), and NVL() Functions Suppose that the "UnitsOnOrder" column is optional, and may contain NULL values. Look at the following SELECT statement: SELECT ProductName, UnitPrice * (UnitsInStock + UnitsOnOrder) FROM Products; In the example above, if any of the "UnitsOnOrder" values are NULL, the result will be NULL. ________________________________________
SQL Injection
SQL Injection SQL injection is a code injection technique that might destroy your database. SQL injection is one of the most common web hacking techniques. SQL injection is the placement of malicious code in SQL statements, via web page input. ________________________________________ SQL in Web Pages SQL injection usually occurs when you ask a user for input, like their username/userid, and instead of a name/id, the user gives you an SQL statement that you will unknowingly run on your database. Look at the following example which creates a SELECT statement by adding a variable (txtUserId) to a select string. The variable is fetched from user input (getRequestString):
Introduction to SQL
Introduction to SQL What is SQL? • SQL stands for Structured Query Language • SQL lets you access and manipulate databases • SQL became a standard of the American National Standards Institute (ANSI) in 1986, and of the International Organization for Standardization (ISO) in 1987 ________________________________________ What Can SQL do? • SQL can execute queries against a database • SQL can retrieve data from a database • SQL can insert records in a database • SQL can update records in a database • SQL can delete records from a database • SQL can create new databases • SQL can create new tables in a database • SQL can create stored procedures in a database • SQL can create views in a database • SQL can set permissions on tables, procedures, and views
HTML Quotation and Citation
HTML Quotation and Citation Elements Quotation Here is a quote from WWF's website: For 50 years, WWF has been protecting the future of nature. The world's leading conservation organization, WWF works in 100 countries and is supported by 1.2 million members in the United States and close to 5 million globally. » ________________________________________ HTML for Short Quotations The HTML element defines a short quotation. Browsers usually insert quotation marks around the element.
HTML Text Formatting
HTML Text Formatting Text Formatting This text is bold This text is italic This is subscript and superscript » ________________________________________ HTML Formatting Elements In the previous chapter, you learned about the HTML style attribute. HTML also defines special elements for defining text with a special meaning. HTML uses elements like and for formatting output, like bold or italic text. Formatting elements were designed to display special types of text: • - Bold text • - Important text • - Italic text • - Emphasized text • - Marked text • - Small text • - Deleted text • - Inserted text • - Subscript text • - Superscript text ________________________________________
HTML Block and Inline Elements
HTML Block and Inline Elements Every HTML element has a default display value depending on what type of element it is. The two display values are: block and inline. ________________________________________ Block-level Elements A block-level element always starts on a new line and takes up the full width available (stretches out to the left and right as far as it can). The element is a block-level element. Example Hello World Try it Yourself » Block level elements in HTML:
HTML Images
HTML Images Images can improve the design and the appearance of a web page. ________________________________________ Example » Example » Example » ________________________________________ HTML Images Syntax In HTML, images are defined with the tag. The tag is empty, it contains attributes only, and does not have a closing tag. The src attribute specifies the URL (web address) of the image: ________________________________________
HTML Iframes
HTML Iframes frame Syntax An HTML iframe is defined with the tag: The src attribute specifies the URL (web address) of the inline frame page. ________________________________________ Iframe - Set Height and Width Use the height and width attributes to specify the size of the iframe. The height and width are specified in pixels by default: Example Try it Yourself » Or you can use CSS to set the height and width of the iframe: Example Try it Yourself »