PostgreSQL Tutorial

Data Types

Querying & Filtering Data

Managing Tables

Modifying Data

Conditionals

Control Flow

Transactions & Constraints

Working with JOINS & Schemas

Roles & Permissions

Working with Sets

Subquery & CTEs

User-defined Functions

Important In-Built Functions

PostgreSQL PL/pgSQL

Variables & Constants

Stored Procedures

Working with Triggers

Working with Views & Indexes

Errors & Exception Handling

PostgreSQL - Assert

PostgreSQL does not have a built-in ASSERT keyword or statement like some other programming or scripting languages, which is used for debugging or ensuring that certain conditions hold true.

However, you can use various techniques and functions to achieve similar functionality in PostgreSQL:

1. Using PL/pgSQL with RAISE EXCEPTION:

Within a PL/pgSQL function or stored procedure, you can use the RAISE EXCEPTION statement to throw an error when a certain condition isn't met:

CREATE OR REPLACE FUNCTION example_assert(val integer) RETURNS void AS $$
BEGIN
    IF val <= 0 THEN
        RAISE EXCEPTION 'Value must be greater than 0';
    END IF;
    -- Rest of the function logic
END;
$$ LANGUAGE plpgsql;

Here, if the provided val is less than or equal to 0, the function will raise an exception and stop executing.

2. Using CHECK Constraints:

For tables, you can use the CHECK constraint to ensure that certain conditions are met for the values in specific columns:

CREATE TABLE example (
    id serial PRIMARY KEY,
    positive_value integer CHECK (positive_value > 0)
);

Here, any attempts to insert a non-positive value into the positive_value column will result in an error.

3. Using Triggers:

Triggers can be used to intercept INSERT, UPDATE, DELETE, etc., operations on tables and assert certain conditions. If these conditions are not met, an error can be raised to prevent the operation:

CREATE OR REPLACE FUNCTION trg_check_value() RETURNS TRIGGER AS $$
BEGIN
    IF NEW.value_column <= 0 THEN
        RAISE EXCEPTION 'Value in value_column must be greater than 0';
    END IF;
    RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER trigger_name BEFORE INSERT OR UPDATE ON table_name
FOR EACH ROW EXECUTE FUNCTION trg_check_value();

Remember that while these methods can mimic assert-like behavior, they have different purposes and side-effects, so use them judiciously based on your application requirements.

Using ASSERT in PostgreSQL for data validation:

Description: Employing ASSERT to validate data integrity within PL/pgSQL functions.

Code Example:

CREATE OR REPLACE FUNCTION validate_data(value INT)
RETURNS VOID AS $$
BEGIN
  ASSERT value > 0, 'Value must be greater than 0';
  -- Further logic if assertion is true
END;
$$ LANGUAGE plpgsql;

Asserting conditions in PL/pgSQL functions:

Description: Asserting conditions within PL/pgSQL functions for robust programming.

Code Example:

CREATE OR REPLACE FUNCTION your_function()
RETURNS VOID AS $$
BEGIN
  ASSERT condition, 'Assertion failed';
  -- Rest of the function logic
END;
$$ LANGUAGE plpgsql;

Error handling with ASSERT in PostgreSQL:

Description: Utilizing ASSERT for early error detection and handling.

Code Example:

CREATE OR REPLACE FUNCTION handle_error(value INT)
RETURNS VOID AS $$
BEGIN
  ASSERT value IS NOT NULL, 'Value cannot be NULL';
  -- Further logic if assertion is true
EXCEPTION
  WHEN OTHERS THEN
    -- Handle exception
END;
$$ LANGUAGE plpgsql;

When to use ASSERT in PostgreSQL programming:

Description: Knowing scenarios where ASSERT is beneficial for data validation.

Code Example:

CREATE OR REPLACE FUNCTION your_function()
RETURNS VOID AS $$
BEGIN
  -- Business logic
  ASSERT condition, 'Unexpected condition encountered';
  -- More logic
END;
$$ LANGUAGE plpgsql;

Writing custom assertions in PostgreSQL:

Description: Creating custom assertions for specific conditions.

Code Example:

CREATE OR REPLACE FUNCTION custom_assertion(value INT)
RETURNS VOID AS $$
BEGIN
  ASSERT value BETWEEN 1 AND 100, 'Value must be between 1 and 100';
  -- Further logic if assertion is true
END;
$$ LANGUAGE plpgsql;

Debugging with ASSERT in PostgreSQL functions:

Description: Using ASSERT for debugging and identifying issues during development.

Code Example:

CREATE OR REPLACE FUNCTION debug_function()
RETURNS VOID AS $$
BEGIN
  ASSERT debug_condition, 'Debugging assertion failed';
  -- Debugging logic
END;
$$ LANGUAGE plpgsql;

ASSERT vs RAISE EXCEPTION in PostgreSQL:

Description: Contrasting ASSERT with RAISE EXCEPTION for error handling.

Code Example:

CREATE OR REPLACE FUNCTION assert_vs_exception(value INT)
RETURNS VOID AS $$
BEGIN
  ASSERT value > 0, 'Value must be greater than 0';
  -- Equivalent using RAISE EXCEPTION
  IF value <= 0 THEN
    RAISE EXCEPTION 'Value must be greater than 0';
  END IF;
  -- Further logic
END;
$$ LANGUAGE plpgsql;

Conditional assertions in PostgreSQL:

Description: Introducing conditional assertions for flexible validation.

Code Example:

CREATE OR REPLACE FUNCTION conditional_assertion(value INT, condition BOOLEAN)
RETURNS VOID AS $$
BEGIN
  ASSERT condition, 'Custom condition failed';
  -- Further logic if assertion is true
END;
$$ LANGUAGE plpgsql;