SQL vs. PL-SQL:

• SQL: A universal query language for relational databases. It allows you to interact with data using standardized commands for tasks like retrieval, insertion, updates, and deletion.
• PL-SQL: An extension for SQL specifically within the Oracle database environment. It adds procedural programming capabilities like loops, conditional statements (if/else), functions, variables, and exception handling on top of core SQL functionality.
• Think of SQL as a general toolset for working with relational databases, and PL-SQL as an extension kit that adds extra functionalities specific to the Oracle database.

The full form of PL-SQL is Procedural Language extensions to the Structured Query Language.

PL-SQL vs. T-SQL:

1. Focus: Both are extensions to SQL for specific database environments, but for different products.
1. PL-SQL
2. T-SQL (Transact-SQL)
2. Functionality: Both offer procedural programming capabilities on top of core SQL, but with slight variations.
1. PL-SQL
2. T-SQL
3. Availability: PL-SQL is specific to the Oracle database, while T-SQL is used within the Microsoft SQL Server environment.

PL-SQL straddles the line. It has its own syntax and can build complex programs, but it's designed specifically for the Oracle database. Think of it as a powerful extension to SQL that lets you write programs within the Oracle environment.

Here's a basic roadmap for writing PL-SQL code:

• Understand SQL
• Learn PL-SQL syntax 
• Develop logic 
• Use an IDE 
• Test and refine

Yes, PL-SQL skills can be a valuable career asset. The demand for Oracle developers is high, and expertise in PL-SQL positions you for well-paying jobs. With strong skills, you can work on interesting database-driven projects and enjoy stability within the Oracle ecosystem.

While there isn't a single inventor credited for PL-SQL, its development is closely associated with Peter Clare. He played a pivotal role in shaping the language during his time at Oracle Corporation.

Generally, SQL is faster than PL-SQL for simple tasks.

Here are a few ways to run PL-SQL code:

• SQL*Plus 
• SQL Developer
• Embedded in Applications
• Web-based interfaces