Constraints in sql

RULES ABOUT THE COLUMNS IN TABLE
NOT NULL 	 # Ensures a column cannot have a NULL value
UNIQUE 		 # Ensures all values in a column are unique
PRIMARY KEY  # Identifies a record in a table, is NOT NULL & UNIQUE
FOREIGN KEY  # References a unique record from another table
CHECK		 # Ensures all column values satisfy a condition
DEFAULT		 # Set a default value for a column if none is entered
INDEX		 # Quick way of retrieving records from database

Sql constarint

It creates a new constraint on an existing table, which is used to specify
rules for any data in the table.
Example: Adds a new PRIMARY KEY constraint named ‘user’ on columns
ID and SURNAME.
ALTER TABLE users
ADD CONSTRAINT user PRIMARY KEY (ID, SURNAME);

Similar codes

2 votes155 views5 answers
Ng class in angular
TypeScript
0 vote171 views2 answers
Ixl ansers
TypeScript
0 vote172 views1 answer
Test if parameter supports null reflection
TypeScript
0 vote156 views3 answers
Get weights of a layer keras
TypeScript
6 votes157 views4 answers
Property 'style' does not exist on type 'Element'.ts(2339)
TypeScript
2 votes189 views1 answer
Drop table if it exists mysql
TypeScript
0 vote146 views1 answer
Reach router path typescript error
TypeScript
2 votes149 views2 answers
Typescript on window resize
TypeScript
0 vote156 views1 answer
Websockets socketio flask
TypeScript
0 vote150 views1 answer
Typescript get the time moment
TypeScript