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Study Notes DBMS & SQL

SQL Queries, Joins & Aggregate Functions

SQL Clauses Execution Order, Joins & Aggregate Functions Revision Sheet

Exact order of SQL execution, NULL handling in COUNT(*) vs COUNT(col), and Correlated Subquery shortcuts.

### 1. Logical Order of SQL Query Execution
Even though we write `SELECT` first, the database engine executes clauses in this exact order:
1. `FROM` & `JOIN` (Cartesian product and join pred...

Exams: HPSC PGT CS, KVS PGT / TGT, NVS PGT CS, RPSC / State Programmer

Study Notes Operating System (OS)

Deadlocks & Banker's Algorithm

Deadlock Necessary Conditions, Avoidance & Banker's Algorithm Complete Notes

High-yield revision notes on Coffman's 4 conditions, Resource Allocation Graph (RAG), and Safe Sequence formula.

### 1. Four Necessary Conditions for Deadlock (Coffman Conditions)
A deadlock situation can arise if and only if the following four conditions hold simultaneously in a system:
1. **Mutual Ex...

Exams: HPSC PGT CS, KVS PGT / TGT, RPSC / State Programmer, Computer Instructor