Error Handling in SQL Stored Procedures – TRY...CATCH, DECLARE CONTINUE HANDLER & Examples

Introduction

In SQL, text data types are used to store alphanumeric values like names, addresses, emails, and descriptions. Choosing the correct text type — CHAR, VARCHAR, or TEXT — is important for optimizing storage space, query speed, and database performance.

In this section, you'll learn the definitions, differences, and best use cases for each text data type.

1. CHAR (Fixed-Length String)

CHAR is used to store fixed-length strings. If the stored string is shorter than the defined length, SQL automatically pads it with spaces to match the specified size.

Features:

• Fixed length
• Fast and predictable performance
• Uses extra storage if the data is often shorter than the specified length

Syntax:

column_name CHAR(length);

length = number of characters (1 to 255 depending on the database system)

Example:

CREATE TABLE countries (
country_code CHAR(2),
country_name CHAR(50)
    );

country_code like 'US', 'IN', 'UK' will always take 2 characters.

When to Use CHAR:

• Data with a constant size, such as country codes, gender ('M', 'F'), state abbreviations
• Fixed-format fields like credit card types ('VISA', 'MC')
• When exact storage size is known and consistent

2. VARCHAR (Variable-Length String)

VARCHAR stands for Variable Character. It stores variable-length strings, meaning only the actual characters are stored without unnecessary padding.

Features:

• Variable length
• More space-efficient than CHAR for varying-length text
• Slightly slower than CHAR when processing large volumes (because of extra calculations for string lengths)

Syntax:

column_name VARCHAR(length);

length = maximum number of characters allowed

Example:

CREATE TABLE employees (
first_name VARCHAR(50),
email VARCHAR(100)
    );

Names and emails can vary in length, making VARCHAR ideal.

When to Use VARCHAR:

• Data with unpredictable or variable length
• Names, emails, addresses, and descriptions under 255-65535 characters
• Most general-purpose text fields

3. TEXT (Large Text Field)

TEXT is used to store large amounts of text like long descriptions, blog posts, comments, or articles.

Features:

• Meant for large text storage (up to 65,535 characters for standard TEXT in MySQL)
• Cannot have a default value (in some databases like MySQL)
• TEXT fields are stored outside the main table with a pointer reference
• Different variants exist (TINYTEXT, MEDIUMTEXT, LONGTEXT) for various sizes

Syntax:

column_name TEXT;

Example:

CREATE TABLE articles (
id INT,
title VARCHAR(255),
body TEXT
   );

body will store the full article content, which can be very large.

When to Use TEXT:

• Long-form text fields (comments, articles, reviews, reports)
• Data that exceeds normal VARCHAR limits
• When exact storage requirements are unknown or potentially very large

Quick Comparison: CHAR vs VARCHAR vs TEXT

Important Tips

• Use CHAR only when all values will be exactly the same length
• VARCHAR is the best choice for most standard text fields
• Reserve TEXT for content that exceeds VARCHAR limits
• Consider VARCHAR(MAX) in SQL Server for large text that might need indexing
• Be aware that TEXT fields may have limitations on default values and full-text indexing

Why Error Handling Matters in SQL Procedures

When running a stored procedure, unexpected errors such as constraint violations, invalid input, or runtime exceptions may occur. Without error handling, these can crash the process or leave the database in an inconsistent state.

Proper error handling helps:

• Catch and manage errors gracefully
• Log issues for debugging
• Maintain database stability
• Prevent incomplete or corrupted data

Error Handling in MySQL Stored Procedures

MySQL uses the DECLARE ... HANDLER statement

Syntax:

DECLARE handler_type HANDLER
FOR condition_value
    statement;

Example 1: Basic Error Handling with CONTINUE

DELIMITER //

CREATE PROCEDURE SafeInsert()
BEGIN
  DECLARE CONTINUE HANDLER FOR SQLEXCEPTION
    BEGIN
      SELECT 'An error occurred during INSERT operation' AS ErrorMessage;
    END;

  INSERT INTO customers(id, name) VALUES (1, 'John');  -- Assume ID 1 already exists
END //

DELIMITER ;

Explanation: If the insert fails (e.g., due to primary key conflict), the handler will catch the error and display a message without crashing the procedure.

Example 2: EXIT Handler with Variable Logging

DELIMITER //

CREATE PROCEDURE DivideNumbers(IN a INT, IN b INT, OUT result INT)
BEGIN
  DECLARE EXIT HANDLER FOR SQLEXCEPTION
    SET result = NULL;

  IF b = 0 THEN
    SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Division by zero';
  ELSE
    SET result = a / b;
  END IF;
END //

DELIMITER ;

Usage:

CALL DivideNumbers(10, 0, @output);
SELECT @output;  -- Returns NULL due to error

Example 3: Custom Error Using SIGNAL (MySQL 5.5+)

SIGNAL SQLSTATE '45000'
SET MESSAGE_TEXT = 'Custom error message';

Use SIGNAL to manually raise exceptions with custom messages.

MySQL Error Handlers: CONTINUE vs EXIT

Best Practices for Error Handling in SQL

• Always use handlers in procedures that perform DML operations (INSERT, UPDATE, DELETE)
• Use EXIT handlers for critical operations that must stop on error
• Use SIGNAL to raise custom errors when needed
• Consider writing errors into a log table for auditing and debugging