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

0 vote225 views1 answer
Loop trhough list of lists in python and find single elements
TypeScript
0 vote182 views1 answer
Primeng dropdown formControlName setValue
TypeScript
0 vote180 views1 answer
"Property 'mocha' does not exist on type 'Cypress & EventEmitter'."
TypeScript
-1 vote201 views1 answer
How to clear all the dropdown elements in jquery
TypeScript
0 vote180 views1 answer
Ngclass stackoverflow
TypeScript
0 vote178 views1 answer
W/TextToSpeech: speak failed: not bound to TTS engine site:stackoverflow.com
TypeScript
0 vote299 views1 answer
Curl -s "http://google.com?[1-1000]"
TypeScript
4 votes185 views1 answer
React typescript scss
TypeScript
1 vote184 views1 answer
Edit card-deck breakingpoints bootstrap
TypeScript
1 vote190 views1 answer
"mat-chip-list" is not a known element:
TypeScript