Description:
This PR updates the SQL document to be fully compatible with PostgreSQL, while maintaining the original structure and comments.

Changes made:

• Table creation & inserts
  • Fixed numeric default for budget ('undecided' → 0.00).
  • Removed duplicate inserts for primary key dept_name.
• ALTER TABLE
  • Removed AFTER column (PostgreSQL does not support it).
  • Replaced MODIFY COLUMN with ALTER COLUMN ... TYPE.
• LIMIT / OFFSET queries
  • Replaced MySQL-style LIMIT m,n with PostgreSQL-compatible LIMIT n OFFSET m.
• JOINs
  • Replaced placeholder [LEFT|RIGHT] JOIN with LEFT JOIN.
• Triggers
  • Converted MySQL DELIMITER style triggers to PostgreSQL CREATE FUNCTION ... RETURNS TRIGGER.
  • Fixed ELSEIF → ELSIF.
• Other queries
  • Preserved original query structure and comments.
  • Ensured syntax compatibility with PostgreSQL.

Notes:

• Placeholders like TABLE_NAME, TABLE1, TABLE2, n, m, and CONDITION should be replaced with actual values before running the queries.
• This PR does not modify business logic, only fixes syntax and compatibility issues.