"I asked this question So many times"


No, you didnt ask that... You've asked things like:

"If Oracle is a Big C program There Must be a compiler to compile the c program? and also i want to know what are this first native compilation and plsql engine sql engine. "

"Do we have any components like compiler,interpreter and assebler,jit(we have them in programing languages to check data and convert data into machine language for computer understanding)?"

"If not there any component like that how data can be handled by computer which we call as server? "


But anyway....

SQL engine - the part of the database kernel that processes a SQL statement submitted by you (or a program).

Optimizer - part of the SQL engine. Works out the way we will execute a SQL statement (eg by index, or full table scan) based on a costing algorithm that assigns a resource cost to each possible way of running a SQL statement.

PL/SQL engine - the part of the database kernel that allows a PLSQL, ie, 3GL like program to run on the database server. PLSQL, like any other program, can also issue SQL statements - these will be passed to the SQL engine for processing.