CREATE TABLE Reviews (
    review_id INT PRIMARY KEY AUTO_INCREMENT,
    customer_id INT NOT NULL,
    restaurant_id INT NOT NULL,
    order_date DATE NOT NULL,
    rating INT CHECK (rating BETWEEN 1 AND 5),
    comment TEXT,
    CONSTRAINT unique_review UNIQUE (customer_id, restaurant_id, order_date, review_id)
);
INSERT INTO Reviews (customer_id, restaurant_id, order_date, rating, comment) VALUES
-- January Reviews
(1, 1, DATE_SUB(CURDATE(), INTERVAL 1 MONTH), 5, 'Amazing food!'),
(2, 1, DATE_SUB(CURDATE(), INTERVAL 1 MONTH), 4, 'Great service.'),
(3, 2, DATE_SUB(CURDATE(), INTERVAL 1 MONTH), 3, 'Good but overpriced.'),
(4, 2, DATE_SUB(CURDATE(), INTERVAL 1 MONTH), 5, 'Excellent ambiance.'),
(5, 3, DATE_SUB(CURDATE(), INTERVAL 1 MONTH), 4, 'Loved the seafood.'),
(6, 3, DATE_SUB(CURDATE(), INTERVAL 1 MONTH), 3, 'Average taste.'),
(7, 1, DATE_SUB(CURDATE(), INTERVAL 1 MONTH), 5, 'Perfect meal!'),
(8, 2, DATE_SUB(CURDATE(), INTERVAL 1 MONTH), 4, 'Nice atmosphere.'),

-- February Reviews
(1, 1, DATE_SUB(CURDATE(), INTERVAL 2 MONTH), 5, 'Delicious!'),
(2, 1, DATE_SUB(CURDATE(), INTERVAL 2 MONTH), 4, 'Good service.'),
(3, 2, DATE_SUB(CURDATE(), INTERVAL 2 MONTH), 3, 'A bit salty.'),
(4, 2, DATE_SUB(CURDATE(), INTERVAL 2 MONTH), 5, 'Great experience.'),
(5, 3, DATE_SUB(CURDATE(), INTERVAL 2 MONTH), 4, 'Tasty food.'),
(6, 3, DATE_SUB(CURDATE(), INTERVAL 2 MONTH), 3, 'Could be better.'),
(7, 1, DATE_SUB(CURDATE(), INTERVAL 2 MONTH), 4, 'Friendly staff.'),
(8, 2, DATE_SUB(CURDATE(), INTERVAL 2 MONTH), 5, 'Highly recommend!'),

-- March Reviews
(1, 1, DATE_SUB(CURDATE(), INTERVAL 3 MONTH), 5, 'Fantastic!'),
(2, 1, DATE_SUB(CURDATE(), INTERVAL 3 MONTH), 4, 'Quick service.'),
(3, 2, DATE_SUB(CURDATE(), INTERVAL 3 MONTH), 3, 'Mediocre taste.'),
(4, 2, DATE_SUB(CURDATE(), INTERVAL 3 MONTH), 5, 'Best meal ever!'),
(5, 3, DATE_SUB(CURDATE(), INTERVAL 3 MONTH), 4, 'Authentic flavors.'),
(6, 3, DATE_SUB(CURDATE(), INTERVAL 3 MONTH), 3, 'Not bad.'),
(7, 1, DATE_SUB(CURDATE(), INTERVAL 3 MONTH), 5, 'Loved everything!'),
(8, 2, DATE_SUB(CURDATE(), INTERVAL 3 MONTH), 4, 'Good but pricey.'),
-- Duplicate Records (Same customer, restaurant, and order_date)
(1, 1, DATE_SUB(CURDATE(), INTERVAL 1 MONTH), 5, 'Amazing food!'),  -- Duplicate of (1,1)
(2, 1, DATE_SUB(CURDATE(), INTERVAL 1 MONTH), 4, 'Great service.'), -- Duplicate of (2,1)
(3, 2, DATE_SUB(CURDATE(), INTERVAL 2 MONTH), 3, 'A bit salty.'),   -- Duplicate of (3,2)
(4, 2, DATE_SUB(CURDATE(), INTERVAL 3 MONTH), 5, 'Best meal ever!'), -- Duplicate of (4,2)
(5, 3, DATE_SUB(CURDATE(), INTERVAL 3 MONTH), 4, 'Authentic flavors.'); -- Duplicate of (5,3)

 
by

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About MySQL

MySQL is a open-source, free and very popular relational database management system which is developed, distributed and supported by Oracle corporation.

Key Features:

  • Open-source relational database management systems.
  • Reliable, very fast and easy to use database server.
  • Works on client-server model.
  • Highly Secure and Scalable
  • High Performance
  • High productivity as it uses stored procedures, triggers, views to write a highly productive code.
  • Supports large databases efficiently.
  • Supports many operating systems like Linux*,CentOS*, Solaris*,Ubuntu*,Windows*, MacOS*,FreeBSD* and others.

Syntax help

Commands

1. CREATE

CREATE TABLE table_name (
                column1 datatype,
                column2 datatype,
                ....);

Example

CREATE TABLE EMPLOYEE (
  empId INTEGER PRIMARY KEY,
  name TEXT NOT NULL,
  dept TEXT NOT NULL
);

2. ALTER

ALTER TABLE Table_name ADD column_name datatype;

Example

INSERT INTO EMPLOYEE VALUES (0001, 'Dave', 'Sales');

3. TRUNCATE

TRUNCATE table table_name;

4. DROP

DROP TABLE table_name;

5. RENAME

RENAME TABLE table_name1 to new_table_name1; 

6. COMMENT

Single-Line Comments:

 --Line1;

Multi-Line comments:

   /* Line1,
   Line2 */

DML Commands

1. INSERT

INSERT INTO table_name (column1, column2, column3, ...) VALUES (value1, value2, value3, ...);

Note: Column names are optional.

Example

INSERT INTO EMPLOYEE VALUES (0001, 'Ava', 'Sales');

2. SELECT

SELECT column1, column2, ...
FROM table_name
[where condition]; 

Example

SELECT * FROM EMPLOYEE where dept ='sales';

3. UPDATE

UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition; 

Example

UPDATE EMPLOYEE SET dept = 'Sales' WHERE empId='0001'; 

4. DELETE

DELETE FROM table_name where condition;

Example

DELETE from EMPLOYEE where empId='0001'; 

Indexes

1. CREATE INDEX

  CREATE INDEX index_name on table_name(column_name);
  • To Create Unique index:
  CREATE UNIQUE INDEX index_name on table_name(column_name);

2. DROP INDEX

DROP INDEX index_name ON table_name;

Views

1. Create a View

Creating a View:
CREATE VIEW View_name AS 
Query;

2. How to call view

SELECT * FROM View_name;

3. Altering a View

ALTER View View_name AS 
Query;

4. Deleting a View

DROP VIEW View_name;

Triggers

1. Create a Trigger

CREATE TRIGGER trigger_name trigger_time trigger_event
    ON tbl_name FOR EACH ROW [trigger_order] trigger_body
/* where
trigger_time: { BEFORE | AFTER }
trigger_event: { INSERT | UPDATE | DELETE }
trigger_order: { FOLLOWS | PRECEDES } */

2. Drop a Trigger

DROP TRIGGER [IF EXISTS] trigger_name;

Stored Procedures

1. Create a Stored Procedure

CREATE PROCEDURE sp_name(p1 datatype)
BEGIN
/*Stored procedure code*/
END;

2. How to call Stored procedure

CALL sp_name;

3. How to delete stored procedure

DROP PROCEDURE sp_name;

Joins

1. INNER JOIN

SELECT * FROM TABLE1 INNER JOIN TABLE2 where condition;

2. LEFT JOIN

SELECT * FROM TABLE1 LEFT JOIN TABLE2 ON condition;

3. RIGHT JOIN

SELECT * FROM TABLE1 RIGHT JOIN TABLE2 ON condition;

4. CROSS JOIN

SELECT select_list from TABLE1 CROSS JOIN TABLE2;