php - What is a Parent table and a Child table in Database? - Stack Overflow
In this model, the employee data table represents the "parent". A Quick-Start Tutorial on Relational Database Design Gather the requirements and define the objective of your database, e.g.. For example, an unique number customerID can be used as the primary key for the . A foreign key of a child table is a primary key of a parent table, used to reference the parent table. Parent-Child Relationship play an important role to get into the designing the data Let's have the simple example of the Parent and Child. It will be helpful for us to get the best use of the Data Definition Language (DDL).
Keeping them inside the Products table results in many empty spaces in those records without these optional data.
parent-child Definition from PC Magazine Encyclopedia
Furthermore, these large data may degrade the performance of the database. A record will only be created for those products with optional data. The two tables, Products and ProductDetails, exhibit a one-to-one relationship. That is, for every row in the parent table, there is at most one row possibly zero in the child table. The same column productID should be used as the primary key for both tables.
Some databases limit the number of columns that can be created inside a table. You could use a one-to-one relationship to split the data into two tables. One-to-one relationship is also useful for storing certain sensitive data in a secure table, while the non-sensitive ones in the main table.
Column Data Types You need to choose an appropriate data type for each column. Commonly data types include: Normalization Apply the so-called normalization rules to check whether your database is structurally correct and optimal. First Normal Form 1NF: A table is 1NF if every cell contains a single value, not a list of values.
Hierarchical database model
This properties is known as atomic. Instead, you should create another table using one-to-many relationship. Second Normal Form 2NF: A table is 2NF, if it is 1NF and every non-key column is fully dependent on the primary key.
Furthermore, if the primary key is made up of several columns, every non-key column shall depend on the entire set and not part of it. If unitPrice is dependent only on productID, it shall not be kept in the OrderDetails table but in the Products table. On the other hand, if the unitPrice is dependent on the product as well as the particular order, then it shall be kept in the OrderDetails table.
Third Normal Form 3NF: A table is 3NF, if it is 2NF and the non-key columns are independent of each others. In other words, the non-key columns are dependent on primary key, only on the primary key and nothing else. For example, suppose that we have a Products table with columns productID primary keyname and unitPrice. The column discountRate shall not belong to Products table if it is also dependent on the unitPrice, which is not part of the primary key.
At times, you may decide to break some of the normalization rules, for performance reason e. Make sure that you fully aware of it, develop programming logic to handle it, and properly document the decision. Integrity Rules You should also apply the integrity rules to check the integrity of your design: The primary key cannot contain NULL.
Otherwise, it cannot uniquely identify the row. For composite key made up of several columns, none of the column can contain NULL. Each foreign key value must be matched to a primary key value in the table referenced or parent table. You can insert a row with a foreign key in the child table only if the value exists in the parent table.
If the value of the key changes in the parent table e. You could either a disallow the changes; b cascade the change or delete the records in the child tables accordingly; c set the key value in the child tables to NULL. Most RDBMS can be setup to perform the check and ensure the referential integrity, in the specified manner. Beside the above two general integrity rules, there could be integrity validation pertaining to the business logic, e.
These could be carried out in validation rule for the specific column or programming logic. Column Indexing You could create index on selected column s to facilitate data searching and retrieval. A specialized index e. However, the index needs to be rebuilt whenever a record is changed, which results in overhead associated with using indexes.
However, those tables are only linked to either the table above them or the table below them. This makes them incredibly useful for gathering information that follows a specific order, or dare I say, hierarchy. Let's take a look at some uses of hierarchical databases, as well as see how one would work in the real world.
Uses Hierarchical databases are useful when two conditions are met. Firstly, the data has to follow a hierarchical pattern. This means that there have to be relationships between the data that could have it visually 'stacked'. Think of a family tree and you're getting the idea. Sometimes you'll see this called a parent-child relationship, even though people are not always the sources of the data.
School age During the elementary school years, the child becomes increasingly interested in peers, but this is not be a sign of disinterest in the parent-child relationship.
Rather, with the natural broadening of psychosocial and cognitive abilities, the child's social world expands to include more people and settings beyond the home environment. The parent-child relationship remains the most important influence on the child's development. Children whose parents are both responsive and demanding continue to thrive psychologically and socially during the middle childhood years.
During the school years, the parent-child relationship continues to be influenced by the child and the parents. In most families, patterns of interaction between parent and child are well established in the elementary school years. Adolescence As the child enters adolescencebiological, cognitive, and emotional changes transform the parent-child relationship.
The child's urges for independence may challenge parents' authority.
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Many parents find early adolescence a difficult period. Adolescents fare best and their parents are happiest when parents can be both encouraging and accepting of the child's needs for more psychological independence.
Although the value of peer relations grows during adolescence, the parent-child relationship remains crucial for the child's psychological development. Authoritative parenting that combines warmth and firmness has the most positive impact on the youngster's development. Adolescents who have been reared authoritatively continue to show more success in school, better psychological development, and fewer behavior problems.
Adolescence may be a time of heightened bickering and diminished closeness in the parent-child relationship, but most disagreements between parents and young teenagers are over less important matters, and most teenagers and parents agree on the essentials. By late adolescence most children report feeling as close to their parents as they did during elementary school. Parenting styles Parenting has four main styles: Although no parent is consistent in all situations, parents do follow some general tendencies in their approach to childrearing, and it is possible to describe a parent-child relationship by the prevailing style of parenting.
These descriptions provide guidelines for both professionals and parents interested in understanding how variations in the parent-child relationship affect the child's development. Parenting style is shaped by the parent's developmental history, education, and personality; the child's behavior; and the immediate and broader context of the parent's life. Also, the parent's behavior is influenced by the parent's work, the parents' marriage, family finances, and other conditions likely to affect the parent's behavior and psychological well-being.
In addition, parents in different cultures, from different social classes, and from different ethnic groups rear their children differently. In any event, children's behavior and psychological development are linked to the parenting style with which they are raised. Authoritarian parents Authoritarian parents are rigid in their rules; they expect absolute obedience from the child without any questioning. They also expect the child to accept the family beliefs and principles without questions.
Authoritarian parents are strict disciplinarians, often relying on physical punishment and the withdrawal of affection to shape their child's behavior. Children raised with this parenting style are often moody, unhappy, fearful, and irritable. They tend to be shy, withdrawn, and lack self-confidence.
If affection is withheld, the child commonly is rebellious and antisocial.
Authoritative parents Authoritative parents show respect for the opinions of each of their children by allowing them to be different. Although there are rules in the household, the parents allow discussion if the children do not understand or agree with the rules.
These parents make it clear to the children that although they the parents have final authority, some negotiation and compromise may take place. Authoritative parents are both responsive and demanding; they are firm, but they discipline with love and affection, rather than power, and they are likely to explain rules and expectations to their children instead of simply asserting them.
This style of parenting often results in children who have high self-esteem and are independent, inquisitive, happy, assertive, and interactive. Permissive parents Permissive indulgent parents have little or no control over the behavior of their children.
If any rules exist in the home, they are followed inconsistently. Underlying reasons for rules are given, but the children decide whether they will follow the rule and to what extent.
They learn that they can get away with any behavior.
Indulgent parents are responsive but not especially demanding. They have few expectations of their children and impose little or inconsistent discipline. There are empty threats of punishment without setting limits.
Role reversal occurs; the children act more like the parents, and the parents behave like the children. Children of permissive parents may be disrespectful, disobedient, aggressive, irresponsible, and defiant. They are insecure because they lack guidelines to direct their behavior.
However, these children are frequently creative and spontaneous. Although low in both social responsibility and independence, they are usually more cheerful than the conflicted and irritable children of authoritarian parents. Disengaged parents Finally, disengaged detached parents are neither responsive nor demanding. They may be careless or unaware of the child's needs for affection and discipline.