Constraints and Indexes
Unique Constraint
Preventing Duplicates
A unique constraint says a column value may appear only once.
Program
Play the script to store accounts with unique emails.
unique_constraint.sql
CREATE TABLE accounts (id INTEGER PRIMARY KEY, email TEXT UNIQUE);
INSERT INTO accounts VALUES (1, 'ada@example.com'), (2, 'lin@example.com');
SELECT email FROM accounts ORDER BY email;
UNIQUE
`UNIQUE` prevents duplicate values in a column.
constraint
A constraint is a rule the database enforces.
data quality
Unique emails avoid duplicate account identity.