Steps for Oracle to execute SQL query statements and oraclesql query statements

Steps for Oracle to execute SQL query statements and oraclesql query statements

Steps for Oracle to execute SQL query statements

If you enter the following query statement in SQL * Plus: SELECT * FROM dept;

Query statement processing mainly includes three processes: parse, execute, and fetch ).

　LCompile: During compilation, the server process will put the body of the SQL statement into the library cache of the shared pool and complete the following processing.

First, search for the same SQL statement (body) in the Shared Pool. If not, perform subsequent processing.

Check whether the syntax of the SQL statement is correct.

You can view the data dictionary to check the table and column definitions.

Add the parse locks to the objects to be operated so that the definition of these objects is not changed during the compilation statement.

Check the user permissions of the referenced object.

Generate the optimization and Execution Plan (execution steps) required to execute the SQL statement ).

Load SQL statements and execution plans into the shared SQL zone.

Each of the above operations is followed up only when the processing is correct. If not, an error is returned.

　LRun: The oracle server process starts to execute the SQL statement because it has obtained all the resources and information required to execute the SQL statement.

　LExtract data: The oracle server process selects the required data rows, sorts them as needed, and finally returns the structure to the user (process ).