CREATE TABLE Products (
    ProductID SERIAL PRIMARY KEY,
    ProductName VARCHAR(100),
    Price DECIMAL(10,2),
    Quantity INT
);

INSERT INTO Products (ProductName, Price, Quantity) VALUES
('Laptop', 1200.00, 10),
('Smartphone', 800.00, 15),
('Tablet', 600.00, 20),
('Monitor', 300.00, 12),
('Keyboard', 50.00, 30);

CREATE OR REPLACE FUNCTION UpdateProductPrice(p_ProductID INT, p_NewPrice DECIMAL(10,2))
RETURNS VOID AS $$
BEGIN
    -- Attempt to update the product's price
    UPDATE Products SET Price = p_NewPrice WHERE ProductID = p_ProductID;
    
    -- Check if the update took place
    IF NOT FOUND THEN
        RAISE EXCEPTION 'Product with ID % does not exist.', p_ProductID;
    END IF;
    
EXCEPTION -- exception handler
    WHEN OTHERS THEN -- OTHERS: all the other exceptions (customized)
        -- Handle any exceptions that occur
        RAISE NOTICE 'An error occurred: %', SQLERRM;
END;
$$ LANGUAGE plpgsql;

-- try to observe for the outputs
-- SELECT UpdateProductPrice(1, 1250.00);
-- SELECT * 
-- FROM Products
-- WHERE ProductID = 1;

-- SELECT UpdateProductPrice(999, 1250.00);

CREATE OR REPLACE FUNCTION UpdateProductPriceAndDivide(p_ProductID INT, p_NewPrice DECIMAL(10,2), p_Divisor DECIMAL)
RETURNS VOID AS $$
BEGIN
    
    
    -- Simulate a calculation that might fail
    p_NewPrice := p_NewPrice / p_Divisor;
    
    -- Attempt to update the product's price
    UPDATE Products SET Price = p_NewPrice;
    
    IF NOT FOUND THEN
        RAISE EXCEPTION 'Product with ID % does not exist.', p_ProductID;
    END IF;
    
EXCEPTION
    WHEN DIVISION_BY_ZERO THEN
        RAISE NOTICE 'Division by zero attempted in price update for product ID %.', p_ProductID;
    WHEN OTHERS THEN
        RAISE NOTICE 'An unexpected error occurred: %', SQLERRM;
END;
$$ LANGUAGE plpgsql;

-- try to observe for the outputs
SELECT UpdateProductPriceAndDivide(9999, 1250.00, 2);
SELECT * 
FROM Products;
-- WHERE ProductID = 1;

-- SELECT UpdateProductPriceAndDivide(999, 1250.00, 2);

PostgreSQL online editor

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About PostgreSQL

PostgreSQL is a open source relational database system and is also knows as Postgres.

Key Features:

  • Postgres is not only free and open-source but also it is highly extensible.
  • Custom Data types and funtions from various programming languaues can be introduced and the good part is compiling entire database is not required.
  • ACID(Atomicity, Consistency, Isolation, Durability) compliant.
  • First DBMS which implemented Multi-version concurrency control (MVCC) feature.
  • It's the default database server for MacOS.
  • It supports all major operating systems like Linux, Windows, OpenBSD,FreeBSD etc.

Syntax help

1. CREATE

CREATE command is used to create a table, schema or an index.

Syntax:

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

2. ALTER

ALTER command is used to add, modify or delete columns or constraints from the database table.

Syntax

ALTER TABLE Table_name ADD column_name datatype;

3. TRUNCATE:

TRUNCATE command is used to delete the data present in the table but this will not delete the table.

Syntax

TRUNCATE table table_name;

4. DROP

DROP command is used to delete the table along with its data.

Syntax

DROP TABLE table_name;

5. RENAME

RENAME command is used to rename the table name.

Syntax

ALTER TABLE table_name1 RENAME to new_table_name1;

6. INSERT

INSERT Statement is used to insert new records into the database table.

Syntax

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

7. SELECT

Select statement is used to select data from database tables.

Syntax:

SELECT column1, column2, ...
FROM table_name;

8. UPDATE

UPDATE statement is used to modify the existing values of records present in the database table.

Syntax

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

9. DELETE

DELETE statement is used to delete the existing records present in the database table.

Syntax

DELETE FROM table_name where condition;