How is a SQL statement executed?

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How is a SQL statement executed?

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All SQL statements have to go through the following stages:

  • Parse: Every SQL statement must be parsed. Parsing the statement includes checking the statement's syntax and validating the statement, ensuring that all references to objects are correct, and ensuring that relevant privileges to those objects exist.


  • Bind: After parsing, the Oracle server knows the meaning of the Oracle statement but still may not have enough information to execute the statement. Therefore, the Oracle server may need values for any bind variable in the statement. The process of obtaining these values is called binding variables.


  • Execute: After binding variables, the Oracle server has all the necessary information and resources. At this point, the Oracle server executes the statement.


  • Fetch: In the fetch stage, rows are selected and ordered (if requested by the query), and each successive row retrieves another row of the result until the last row has been fetched. Queries (SELECT statements) can be fetched, but other DML statements cannot be fetched.


    • Note: Some stages can be skipped.


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