Oracle SQL Skill

Query Standards

• Use ANSI SQL join syntax (JOIN ... ON ...) — never comma-separated joins in FROM.
• Always alias tables with meaningful short names: SELECT u.name FROM users u.
• Qualify all column references with the table alias to avoid ambiguity.
• Use UPPER_CASE for SQL keywords (SELECT, FROM, WHERE); use snake_case for identifiers.
• Format complex queries with consistent indentation (2 or 4 spaces); each clause on its own line.
• Use :bind_variable syntax for all user-supplied values — never interpolate strings into SQL.

Indexing

• Add indexes on all columns used in WHERE, JOIN, ORDER BY, and GROUP BY.
• Use composite indexes when queries filter on multiple columns together; put the most selective column first.
• Use function-based indexes for queries that apply functions to indexed columns (e.g., UPPER(email)).
• Use EXPLAIN PLAN FOR ... to inspect execution plans before deploying complex queries.
• Avoid full table scans on large tables — always verify index usage in the plan.