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Oracle PLSQL Interview Questions. Additional Concepts Every Developer Should Know.
The best way of learning something is by asking questions. That's why I've organized this hub in a question-answer format.
The questions range from Basic to Advanced. I gave a concise answer too, only for quick reference and revision. For detailed answer to each question, refer to any Oracle PL/SQL online documentation.
Some of these questions were actually asked in my Job Interviews in the US.
I have added some others which I found interesting. Very useful to know.
What is a cursor ? ( Basic)
- Name or handle to a private SQL area where Oracle parses and fetches query results.
How to control how many cursors are open ?(Intermediate)
- Set OPEN_CURSORS parameter in initialization parameters.
What is shared SQL ? (Intermediate)
-Oracle recognizes similar statements. The SQL area is used many times for similar statements.
What is Parsing ? (Intermediate)
- Syntax checking, privileges checking, allocating Private SQL Area.
What is the difference between anonymous blocks and stored procedures ? ( Basic)
- Anonymous block is compiled only when called.
- Stored procedure is compiled and stored in database with the dependency information as well.
- Former is PL/SQL code directly called from an application. Latter is stored in database.
- Former has declare statement.Latter doesn't.
What are the advantages of procedures ? ( Basic)
- Loaded once and used many times
- Performance better coz all SQL stmts are sent in one go from the application to the database
- Security ( no object privileges are given directly )
- Invoker's rights possible
- Data integrity, productivity
What are standalone procedures ? (Basic)
- Those that are not part of package
How is a PL/SQL program stored in database ? (Advanced)
- Parsed code is stored. It's called P-code
How is a PL/SQL program executed ?(Advanced)
- Prior to Oracle 9i, we have only bytecode and a virtual machine in the database runs it. Later versions have faster native code execution.
- PL/SQL engine is the main component that executes procedural stmt and passes the SQL to the SQL statement executor.
What are the advantages and disadvantages of DBMS_SQL ? (Intermediate)
- It has all the advantages of dynamic sql .. like runtime construction of sql, DDL statements can be executed.
- Its advantage over EXECUTE IMMEDIATE is it can Describe objects
- It's kind of bulky and difficult compared to EXECUTE IMMEDIATE.
What is a package spec and package body ? Why the separation ? ( Basic)
- Spec declares public constructs. Body defines public constructs, additionally declares and defines Private constructs
- Separation helps make development easier
- Dependency is simplified. You can modify body without invalidating dependent objects.
What are the advantages of Packages ? ( Basic)
- Encapsulation of code logic
- Privileges to objects can be controlled
- Loaded once into memory , used subsequently.
- Dependency simplified
- Public/private procs, functions, variables
How do you handle exceptions for bulk operations ? (Intermediate)
- Use the SAVE EXCEPTIONS clause ( FORALL index IN bound_clause SAVE EXCEPTIONS LOOP ... END LOOP )
- Use 'Exceptions When Others' to handle the exceptions
Tell some tips to avoid performance problems in PL/SQL. (Intermediate to Advanced)
- Use FORALL instead of FOR, and use BULK COLLECT to avoid looping many times
- Tune SQL statements to avoid CPU overhead
- Use NOCOPY for OUT and IN OUT if the original value need not be retained. Overhead of keeping a copy of OUT is avoided.
- Reorder conditional tests to put least expensive ones first
- Minimize datatype conversions => Assign data to exact same type variables
- Use PLS_INTEGER for computation intensive code. NUMBER, INTEGER maintain precision and scale but not optimized for performance as additional checks are made to maintain precision and scale.
- Do not use subtypes like POSITIVE, NATURAL, INTEGER as they have additional checks
- Use BINARY_FLOAT, BINARY_DOUBLE
- EXECUTE IMMEDIATE is faster than DBMS_SQL
How to know PL/SQL compile parameters ?(Advanced)
- SHOW PARAMETERS PLSQL
What is MERGE ?( Basic)
- Combination of INSERT and UPDATE
Tell some new features in PL/SQL in 10g (Intermediate to Advanced)
- Regular expression functions REGEXP_LIKE , REGEXP_INSTR, REGEXP_REPLACE, and REGEXP_SUBSTR
- Compile time warnings
- Conditional compilation
- Improvement to native compilation
- BINARY_INTEGER made similar to PLS_INTEGER
- INDICES OF , VALUES OF in FORALL lets you work on non-consecutive indices
- Quoting mechanism . Instead of quoting single quotes twice every time, give your own delimiter to go on using single quotes.
Ex: q'!I'm a string, you're a string.!'
- Flashback Query functions. SCN_TO_TIMESTAMP, TIMESTAMP_TO_SCN
- Implicit conversion between CLOB and NCLOB
- Improved Overloading
- New datatypes BINARY_FLOAT, BINARY_DOUBLE
- Global optimization enabled
- PLS_INTEGER range increased to 32bit
- DYNAMIC WRAP using DBMS_DDL
What is a sequence ? (Basic)
- A database object that offers high-speed access to an integer value
- Guaranteed to be unique (within that sequence).
-Used commonly to generate Primary key values
Folks, check out http://hubpages.com/hub/oracle_sql_plsql for more questions.
COMMENTS AND SUGGESTIONS ARE WELCOME !!!!