Functional Dependency

Functional dependency is a relationship that exists between two attributes. It typically exists between the primary key and non-key attribute within a table.

1. X   →   Y  

The left side of FD is known as a determinant, and the right side of the production is known as a dependent.

For example:

Assume we have an employee table with Emp_Id, Emp_Name, Emp_Addressand  attributes.

Here Emp_Id attribute can uniquely identify the Emp_Name attribute of the employee table because if we know the Emp_Id, we can tell that the employee name is associated with it.

Functional dependency can be written as:

1. Emp_Id → Emp_Name   

We can say that Emp_Name is functionally dependent on Emp_Id.

Types of Functional dependency

1. Trivial functional dependency

• A → B has trivial functional dependency if B is a subset of A.
• The following dependencies are also trivial: A → A, B → B

Example:

1. Consider a table with two columns Employee_Id and Employee_Name.  
2. {Employee_id, Employee_Name}   →    Employee_Id is a trivial functional dependency as   
3. Employee_Id is a subset of {Employee_Id, Employee_Name}.  
4. Also, Employee_Id → Employee_Id and Employee_Name   →    Employee_Name are trivial dependencies too.  

2. Non-trivial functional dependency

• A → B has a non-trivial functional dependency if B is not a subset of A.
• When A intersection B is NULL, then A → B is called a complete non-trivial.

Example:

1. ID   →    Name,  
2. Name   →    DOB  

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Relational Calculus

• Relational calculus is a non-procedural query language. In the non-procedural query language, the user is concerned with the details of how to obtain the end results.
• The relational calculus tells what to do but never explains how to do it.

Types of Relational calculus:

1. Tuple Relational Calculus (TRC)

• The tuple relational calculus is specified to select the tuples in a relation. In TRC, the filtering variable uses the tuples of a relation.
• The result of the relation can have one or more tuples.

Notation:

1. {T | P (T)}   or {T | Condition (T)}   

Where

T is the resulting tuples

P(T) is the condition used to fetch T.

For example:

1. { T.name | Author(T) AND T.article = 'database' }  

OUTPUT: This query selects the tuples from the AUTHOR relation. It returns a tuple with 'name' from Author who has written an article on 'database'.

TRC (tuple relation calculus) can be quantified. In TRC, we can use Existential (∃) and Universal Quantifiers (∀).

For example:

1. { R| ∃T ∈ Authors(T.article='database' AND R.name=T.name)}  

Output: This query will yield the same result as the previous one.

2. Domain Relational Calculus (DRC)

• The second form of relation is known as Domain relational calculus. In domain relational calculus, filtering variable uses the domain of attributes.
• Domain relational calculus uses the same operators as tuple calculus. It uses logical connectives ∧ (and), ∨ (or), and ┓ (not).
• It uses Existential (∃) and Universal Quantifiers (∀) to bind the variable.

Notation:

1. { a1, a2, a3, ..., an | P (a1, a2, a3, ... ,an)}  

Where

a1, a2 are attributes
P stands for formula built by inner attributes

For example:

1. {< article, page, subject > |  ∈ javatpoint ∧ subject = 'database'}  

Output: This query will yield the article, page, and subject from the relational javatpoint, where the subject is a database.

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Integrity Constraints

• Integrity constraints are a set of rules. It is used to maintain the quality of information.
• Integrity constraints ensure that the data insertion, updating, and other processes have to be performed in such a way that data integrity is not affected.
• Thus, integrity constraint is used to guard against accidental damage to the database.

Types of Integrity Constraint

1. Domain constraints

• Domain constraints can be defined as the definition of a valid set of values for an attribute.
• The data type of domain includes string, character, integer, time, date, currency, etc. The value of the attribute must be available in the corresponding domain.

Example:

2. Entity integrity constraints

• The entity integrity constraint states that primary key value can't be null.
• This is because the primary key value is used to identify individual rows in relation and if the primary key has a null value, then we can't identify those rows.
• A table can contain a null value other than the primary key field.

Example:

3. Referential Integrity Constraints

• A referential integrity constraint is specified between two tables.
• In the Referential integrity constraints, if a foreign key in Table 1 refers to the Primary Key of Table 2, then every value of the Foreign Key in Table 1 must be null or be available in Table 2.

Example:

4. Key constraints

• Keys are the entity set that is used to identify an entity within its entity set uniquely.
• An entity set can have multiple keys, but out of which one key will be the primary key. A primary key can contain a unique and null value in the relational table.

Example:

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Blog Word Prefix in post only wordpress URL

 Copy past and check 

1) Add this rewrite at the end of you function.php

function add_rewrite_rules( $wp_rewrite )
{
    $new_rules = array(
        'blog/(.+?)/?$' => 'index.php?post_type=post&name='. $wp_rewrite->preg_index(1),
    );

    $wp_rewrite->rules = $new_rules + $wp_rewrite->rules;
}
add_action('generate_rewrite_rules', 'add_rewrite_rules'); 

function change_blog_links($post_link, $id=0){

    $post = get_post($id);

    if( is_object($post) && $post->post_type == 'post'){
        return home_url('/blog/'. $post->post_name.'/');
    }

    return $post_link;
}
add_filter('post_link', 'change_blog_links', 1, 3);

2) Go to Settings > Permalinks and click Save Changes.

Create a category called blog and use the permalink structure /%category%/%postname%/.

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URL prefix for posts WordPress

 

So I have website on a WordPress engine. And I want to make posts urls looks like coderfunda.blogspot.com or http://coderfunda.blogspot.com/blog/categ-name/post-name/. But everything else will look like http://website.com/page-name/. Just want to add prefix 'blog' to urls for all posts but not pages. My permalink settings is /%postname%/. If i will put /blog/%postname%/ I will have 'blog' prefix in every URL of my site :( I can't find solution in WordPress admin backend and I didn't find any acceptable plugin for this. Any help is appreciated, thanks.

Create a category called blog and use the permalink structure /%category%/%postname%/.

1) Add this rewrite at the end of you function.php

function add_rewrite_rules( $wp_rewrite )
{
    $new_rules = array(
        'blog/(.+?)/?$' => 'index.php?post_type=post&name='. $wp_rewrite->preg_index(1),
    );

    $wp_rewrite->rules = $new_rules + $wp_rewrite->rules;
}
add_action('generate_rewrite_rules', 'add_rewrite_rules'); 

function change_blog_links($post_link, $id=0){

    $post = get_post($id);

    if( is_object($post) && $post->post_type == 'post'){
        return home_url('/blog/'. $post->post_name.'/');
    }

    return $post_link;
}
add_filter('post_link', 'change_blog_links', 1, 3);

2) Go to Settings > Permalinks and click Save Changes.

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URL prefix for posts WordPress | Use Blog Word Prefix in post only wordpress URL

 

This function use in wordpress function.php file in last .

if you want to change url according your post exp.

https://www.blogger.com/blog/category/postname

"blog" is a prefix 

This is use only post not show in page.

then visite permalink and set fist custome/

category/postname

copy past and check 

1) Add this rewrite at the end of you function.php

function add_rewrite_rules( $wp_rewrite )
{
    $new_rules = array(
        'blog/(.+?)/?$' => 'index.php?post_type=post&name='. $wp_rewrite->preg_index(1),
    );

    $wp_rewrite->rules = $new_rules + $wp_rewrite->rules;
}
add_action('generate_rewrite_rules', 'add_rewrite_rules'); 

function change_blog_links($post_link, $id=0){

    $post = get_post($id);

    if( is_object($post) && $post->post_type == 'post'){
        return home_url('/blog/'. $post->post_name.'/');
    }

    return $post_link;
}
add_filter('post_link', 'change_blog_links', 1, 3);

2) Go to Settings > Permalinks and click Save Changes.

Create a category called blog and use the permalink structure /%category%/%postname%/.

2nd 

function add_rewrite_rules( $wp_rewrite )

{

    $new_rules = array(

        'blog/(.+?)/?$' => 'index.php?post_type=post&name='. $wp_rewrite->preg_index(1),

    );

    $wp_rewrite->rules = $new_rules + $wp_rewrite->rules;

}

add_action('generate_rewrite_rules', 'add_rewrite_rules'); 

function change_blog_links($post_link, $id=0){

    $post = get_post($id);

    if( is_object($post) && $post->post_type == 'post'){

        return home_url('/blog/'. $post->post_name.'/');

    }

    return $post_link;

}

add_filter('post_link', 'change_blog_links', 1, 3);

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