SQL Fundamentals · question
Q.06 of 41
What are constraints and what types are available?
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Re-explain
- NOT NULL: Prevents null values
- UNIQUE: Ensures uniqueness across rows
- PRIMARY KEY: Combines NOT NULL and UNIQUE
- FOREIGN KEY: Maintains referential integrity between tables
- CHECK: Validates data against specified conditions
- DEFAULT: Provides default values when none specified
CREATE TABLE orders (
order_id INT PRIMARY KEY,
customer_id INT NOT NULL,
order_date DATE DEFAULT GETDATE(),
total_amount DECIMAL(10,2) CHECK (total_amount > 0),
FOREIGN KEY (customer_id) REFERENCES customers(id)
);
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