Basic Queries MySQL part 2 (Let's fill the table up!) π
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What are the keys in a relational database?
Keys help you uniquely identify a row in the table. It is also used to create relationship amongst various tables in a database.
The major types of keys:-
Primary Key
Candidate Key
Super Key
Foreign Key
Keys help you uniquely identify a row in the table. It is also used to create relationship amongst various tables in a database.
The major types of keys:-
Primary Key
Candidate Key
Super Key
Foreign Key
Super Key: A set of one or more attributes or columns that identify a row/record in the table. It may consist of some columns that are not needed for the unique identification of a row.
Primary Key: A column or a group of columns that can uniquely identify a row/record in the table can become the primary key. It cannot have null or duplicate values in it. It is used to create relationships b/w different tables in a database.
Candidate Key: A set of columns that uniquely identifies a record. It is a super key with no repeated attribute, i.e. the minimal super key is a candidate key, or the candidate key is the proper subset of the super key.
Note: Proper Subset -> If A={1,4,3,5} then B={1,3} is a proper subset of A.
Foreign Key: It is a column of the table used to indicate the primary key of another table. It acts as a cross-reference between two tables.
Foreign Key: It is a column of the table used to indicate the primary key of another table. It acts as a cross-reference between two tables.
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What are CONSTRAINTS?
They are the rules for the columns
Types of Constraints:-
NOT NULL - Guarantees that a column cannot have a NULL value or empty value
UNIQUE - Ensures that all values in a column are different
PRIMARY KEY - A combination of NOT NULL and UNIQUE values
They are the rules for the columns
Types of Constraints:-
NOT NULL - Guarantees that a column cannot have a NULL value or empty value
UNIQUE - Ensures that all values in a column are different
PRIMARY KEY - A combination of NOT NULL and UNIQUE values
DEFAULT - Sets a default value for a column if no value is specified
CHECK - Ensures the values in a column satisfy a specific condition
CHECK - Ensures the values in a column satisfy a specific condition
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Data Types in MySQL
To get you going:-
1. int -> integer (for non decimal values like 1, 2, 3)
2. varchar(size) -> a variable-length string up to a size defined by you
More:-
https ://bit.ly/2S4KHeI
To get you going:-
1. int -> integer (for non decimal values like 1, 2, 3)
2. varchar(size) -> a variable-length string up to a size defined by you
More:-
https ://bit.ly/2S4KHeI
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Inserting Values in a table
Single value at a time: insert into table_name values (data1, data2, data3....)
OR
Multiple values at once: insert into table_name values (data1, data2...), (data1, data2)
Single value at a time: insert into table_name values (data1, data2, data3....)
OR
Multiple values at once: insert into table_name values (data1, data2...), (data1, data2)
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To fetch data from the table, we use the SELECT statement.
Now, we want to fetch all the data we added into the classroom1 table.
For that we do:-
select * from table_name;
* -> means ALL
Now, we want to fetch all the data we added into the classroom1 table.
For that we do:-
select * from table_name;
* -> means ALL
Practice Yourself:-
1) Download MySQL
2) Create a database named "College"
3) Create 3 Tables named "Students", "Teachers", "Departments"
4) Fill those tables using columns and their constraints
1) Download MySQL
2) Create a database named "College"
3) Create 3 Tables named "Students", "Teachers", "Departments"
4) Fill those tables using columns and their constraints
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