Why do we store data in separate tables and not in one big table? Explain to me how we take an ERD and translate boxes and lines in the ERD into a SQL statement. What is needed in order to design an ERD? What is needed to work with multiple tables in a SQL statement?
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Linlan Chen says
If we are storing different types of data for each product’s reviews (i.e., each table has a different set of columns), using a different table per product will be creating an unnecessary nightmare.
Andres Galarza says
I think the answer for why we split data is because a huge database would be very slow, and if it were to be damaged or handicapped, you would lose access to all of the data, not just some.
We use the diagrams to describe how we want the relationship between the entities to exist. Once we have these relationships described, we’re really only using SQL to input them into the tables in a way that supports those relationships and allows for logical queries.
Somayeh Keshtkar says
The reason we do not store all data in one large table is mainly for performance. The larger the table size is, the slower our queries for application, and reporting tools would be. Additionally, it defeats the purpose of relational database design, and make the task of maintaining a database nightmare for its users.
ERD is entity relationship diagram that shows the relation, and connection of various tables in a database. Using ERD, we can see the number of tables, and specific relationship between them in a specific domain of knowledge. The boxes in an ERD diagram represents tables, and whether they have foreign keys or not. The ERD also displays the attributes, or information about that concept, of each table. The connecting line between the boxes displays the relationship between connected tables, or in other words their cardinality. For example we can see the relationships are one to one, one to many, one or more, zero or many, etc.
In order to design an ERD, we need to have a good understanding of domain knowledge, and business model. We need to clarify business terminology, and connect business concepts to database structures. We can then break business entities to tables in ERD that represent a real world concepts. We finally display the business logic between the entities by using connecting lines and cardinality.
In order to work with multiple tables in a SQL statement we need to use join clauses. Join clause is used to combine rows from two or more tables based on foreign key between them. There are various types of join such as left join, right join, full join, and inner and outer join. With each type of join we can target a different subset of combined data between multiple tables.
Karabo Ntokwane says
Data in stored in separate tables to achieve the concept of normalization. Normalization reduces data redundancy and improve data integrity. Normalization helps you to store data with little duplication.
An entity relationship diagram (ERD) is a visual form of relational databases. ERDs model and design relational databases. An example School and Student are entities (tables). In the School table, there are two columns – id and name. id is the primary key (PK) . A primary key is capable in uniquely defining records in a table. Student, another table, has a foreign key column, namely Schoolid. It is a reference to the primary key Id in the School table. ERD can be used to create SQL statements for example to get information from the two tables a JOIN statement will be used. The tables will be joined by primary key-foreign key.
Yijiang Li says
Data should be stored in seperate tables rather than one big table for some reasons. Initially, if one big table is broken, all of the data would be lost. However, seperate tables could reduce the risk of lossing all the data in one accident. Second, seperate tables would be more helpful when you are building a Entity Relationship Diagram (ERD), because ERD needs some lines and arrows to indicate the relatinoship between two factors, seperate tables would be easier to draw those lines and arrows.
Whatever you desgin an ERD or translate it into SQL statement, figuring out the relationship between them should be the initial and essential step. For instance, factor A could have mutiple factor B, but factor B only has one factor A. When you deal with mutiple tables in a SQL statement, making sure the primary key of those tables should be most important thing.
Hanqing Zhou says
In my opinion, there are three main reasons that we need to separate tables: 1) too much information make the system speed becomes slow, 2) to make it easy to check out the specific data, 3) to achieve the concept of normalization.
ERD is entity relationship diagram, we can easily see the information with charts and diagram. If we want to transfer it to SQL we need to use “join” statement.
If we want to design an ERD diagram, we need to know about the relative knowledge and concept of the business. We should also know about the relationship between each entires.
Xinteng Chen says
It is important to separate data into different tables, because it improves the speed of queries In addition, if users put all information together, all information will be lost when the database has problems.
ERD descriptors the relationship between each diagram. There is only one primary key in each table, it connect to the foreign key to the other diagrams if they have the dame column. SQL use these connections to search the data we need. To design ERD, we need to know the relationship of each table to build connections between them. We need to determine the primary key for each table to identify each specific entity, such as ID number. In SQL statement, we need to know the primary key and foreign key, and make them equal to each other when we obtain information in multiple tables.
Zhixin Wei says
MySQL is capable of using only JOIN method, namely NESTED LOOPS. This means that for each record in the driving table, MySQL locates a matching record in the driven table in a loop. Locating a record is quite a costly operation which may take dozens times as long as the pure record scanning. Moving all your records into one table will help you to get rid of this operation, but the table itself grows larger, and the table scan takes longer. If you have lots of records in other tables, then increase in the table scan can overweight benefits of the records being scanned sequentially.
Marsha Billups says
We store data in different tables to reduce risk of losing all data and efficiency when working in relational databases. An ERD is a diagram that shows the fields of each table and how tables relate to other tables. Each table has a primary key and can be related to a another table by the foreign key. Tables can be joined together in various manners (inner join, outer join, etc.)
Heiang Cheung says
We store data in multiple table because it would take to long to scan for the item you’re looking for. An ERD is a diagram that show the relations to each table in a schema. It also show the primary key of each table.
Dongjie Wang says
Why do we store data in separate tables and not in one big table? Explain to me how we take an ERD and translate boxes and lines in the ERD into a SQL statement. What is needed in order to design an ERD? What is needed to work with multiple tables in a SQL statement?
Reasons we store data in separate tables and not in one big table are:
–separate tables can be more efficient when users need to select specific data set
–separate tables can better protect information compared to one big data table
–separate tables can improve queries processing time
the two critical factors in ERD are Entities and Attributes. Each attribute turns into a column (attribute) in the table. To design an ERD, in each table should include a primary key of the table which is unique and usually underlined. in order to work with multiple tables in a SQL statement, we need to understand the relationships between tables and primary key as well as foreign keys.
Raisa Ahmed says
We store data in separate tables and not in one big table for better and faster performance. Entity Relationship Diagram (ERD) is an entity relationship diagram that shows a connection of various tables in a database. The boxes in an Entity Relationship Diagram (ERD) represents tables and whether they have foreign keys/primary keys. The connecting line between the boxes displays the relationship between connected tables. In order to work with multiple tables in a SQL statement we need to use join clauses.
Chenhui Lai says
If store data in one big table, when the big table suffered the natural disaster, theft, physical damage, or human error, all data will be lost. Also, separate tables can improve the efficiency to find valuable data.
The translation is approximate because it is not always feasible to capture all the constraints in the ER design within the relational schema. (In SQL, certain types of constraint, for example, are inefficient to enforce, and so
usually not implemented.)
In order to design ERD, we must know each primary key in every table.
Join clauses is needed in work with multiple tables in SQL statement.
Fraser G says
We don’t store all the data in one big table for a number of reasons, the most important of which are accessibility, performance and redundancy/. Large tables take require more resources to query than two smaller tables. You also don’t want someone to be able to access sensitive information in a table if all they need is public information (in the example of using one big database).
We can use an ERD or entity relationship diagram to query between two sets of data (for example with the *JOIN* command). We use a key as the unique identifier in data to make relational connections. All of this is dependent on understand how the ERD works. The ERD should be set up so that business functions are mapped to the appropriate data. Knowing how the business functions is the most important part of designing an ERD.
Tamekia P. says
We use multiple tables because one table is not efficient. The updates would take massive amounts of time and there is chance of having error. By creating multiple tables and utilizing foreign and primary keys we can query tables against each other using the relation. The boxes in the ERD are the tables and the lines show the relationship – one to one, one to many, many to one and many to many. These are translated in the statements by utilizing the FROM and WHERE portions of the query. You can reference multiples tables by utilizing JOIN.
Folake Stella Alabede says
Data are stored in separate tables for a few reasons.
– Data stored in separated tables makes the data size of each table smaller rather than having all the data stored in a single table. This improves performance and prevents data stored in a central table from crashing which conforms to the principle of Integrity and availability.
– Data stored in separate tables also ensures redundancy as the failure of one table would not affect other tables and data from other tables could be used to reconstruct the failed table.
ERD is an entity relationship diagram which describes the relationship of various tables in a database. To design an ERD, the business terminology must be defined, then business concepts have to be connected to database structures.
For multiple tables in a SQL statement to work, we must use the join clauses.
Yingyan Wang says
Using separate table is more convenient and efficient than using one big table. It will spend too much time to process different data stored in one table. ERD is a good tool to show the relations among multiple tables. To design the ERD diagram. primary key of each table is needed. And by using correct query, it is easy to retrieve data you want from both single table or multiple tables. The correct query statement including JOIN, INNER JOIN, OUTER JOIN and so on.