Oracle and SQL Server Functions differences

Oracle—Function Syntax:
-------------------------------

CREATE OR REPLACE FUNCTION function_name (
param1 IN datatype,
param2 IN datatype
)
RETURN return_datatype
IS
result return_datatype;
BEGIN   
-- Your logic here
result := ...;
RETURN result;
END;

PROGRAM:
---------------
CREATE OR REPLACE FUNCTION GetFullName (
firstName IN VARCHAR2,
lastName IN VARCHAR2
)
RETURN VARCHAR2
IS
fullName VARCHAR2(100);
BEGIN
fullName := firstName || ' ' || lastName;
RETURN fullName;
END;

SQL Server – Function Syntax:
--------------------------------------
1. Scalar Function (returns a single value)

CREATE FUNCTION function_name (@param1 datatype, @param2 datatype)
RETURNS return_datatype
AS
BEGIN
DECLARE @result return_datatype;   
   -- Your logic here
    SET @result = ...;
    RETURN @result;
END;

PROGRAM:
---------------
CREATE FUNCTION GetFullName (@firstName NVARCHAR(50), @lastName NVARCHAR(50))
RETURNS NVARCHAR(100)
AS
BEGIN
    RETURN (@firstName + ' ' + @lastName);
END;

2. Table-Valued Function

Syntax:
---------
CREATE FUNCTION function_name (@param datatype)
RETURNS TABLE
AS
RETURN
(
    SELECT * FROM SomeTable WHERE Column = @param
);

PROGRAM:
---------------
CREATE FUNCTION GetEmployeesByDept(@deptId INT)
RETURNS TABLE
AS
RETURN
(
    SELECT * FROM Employees WHERE DeptID = @deptId
);

* Write a program to get employees based on deptno (Table-Valued Function)

ORACLE:
-------------
CREATE OR REPLACE FUNCTION GetEmployeesByDept
(
    p_deptno IN NUMBER
)
RETURN SYS_REFCURSOR
AS
    emp_cursor SYS_REFCURSOR;
BEGIN
    OPEN emp_cursor FOR
        SELECT * FROM emp WHERE deptno = p_deptno;
    RETURN emp_cursor;
END;
/

SQL:
------
CREATE OR ALTER FUNCTION GetEmployeesByDept
(
@deptno INT
)
RETURNS TABLE
AS
RETURN
(
    SELECT * FROM Emp WHERE Deptno = @deptno
);

SELECT * FROM dbo.GetEmployeesByDept(10);

* Write a program to get Concat employees name, job and sal (Scalar function)

SQL:
------
CREATE OR ALTER FUNCTION CONCAT_EMP_DETAILS
(
@ename NVARCHAR(50),
@job NVARCHAR(50),
@sal int
)
RETURNS NVARCHAR(100)
AS
BEGIN
    RETURN (@ename + ' ' + @job + ' ' + CAST(@sal AS nvarchar));
END;

SELECT dbo.CONCAT_EMP_DETAILS('SMITH', 'CLERK', 3000);

ORACLE:
-------------
CREATE OR REPLACE FUNCTION CONCAT_EMP_DETAILS (
    p_ename IN VARCHAR2,
    p_job   IN VARCHAR2,
    p_sal   IN NUMBER
) RETURN VARCHAR2
IS
    v_result VARCHAR2(200);
BEGIN
    v_result := p_ename || ' ' || p_job || ' ' || TO_CHAR(p_sal);
    RETURN v_result;
END;
/

* Functions do not use EXEC or EXECUTE like stored procedures.
   You can also join it with other tables.

SELECT e.ename, d.dname
FROM dbo.GetEmployeesByDept(20) e
JOIN Dept d ON e.deptno = d.deptno;

* What is the difference between scalar and table-valued functions?

1. Scalar Function

Returns: single value (like `int`, `varchar`, `date`, etc.)

Use case: When you need to compute or return one value from logic or input.

CREATE FUNCTION GetBonus (@salary INT)

RETURNS INT

AS

BEGIN

    RETURN (@salary * 0.10)

END;

* How to use?

SELECT ename, sal, dbo.GetBonus(sal) AS Bonus FROM Emp;

2. Table-Valued Function (TVF)

Returns: table (multiple rows and columns)

Use case: When you want to filter, transform, or return sets of data like a table.

CREATE FUNCTION GetEmployeesByDept(@deptno INT)

RETURNS TABLE

AS

RETURN (

    SELECT * FROM Emp WHERE Deptno = @deptno

);

* How to use?

SELECT * FROM dbo.GetEmployeesByDept(10);

Key Differences:

--------------------

Feature                | Scalar Function                            | Table-Valued Function (TVF)            

---------------------| ------------------------------             | -----------------------------------

Return Type        | Single value                                 | Table (set of rows/columns)            

Used In               | SELECT, WHERE, JOIN, etc.    | FROM clause like a table               

Performance Impact | Often slower in large queries | Usually faster and better for sets     

Example Usage  | `SELECT dbo.GetBonus(sal)`     | `SELECT * FROM dbo.GetEmployees(...)`  

Types                  | Always returns a scalar                | Inline or Multi-statement table-valued 

Oracle and SQL Server Triggers differences

Oracle and SQL Server Triggers differences

ORACLE:
--------------

CREATE OR REPLACE TRIGGER trigger_name
AFTER INSERT ON table_name
FOR EACH ROW
BEGIN
-- Trigger logic here
INSERT INTO audit_table(user_name, action_date)
VALUES (USER, SYSDATE);
END;
/

Program:
-----------

CREATE OR REPLACE TRIGGER trig_emp_table
AFTER DELETE ON EMP
FOR EACH ROW
BEGIN
INSERT INTO emp_trigger_table (empno, ename, job, mgr, hiredate, sal, comm, deptno)
VALUES (:OLD.empno, :OLD.ename, :OLD.job, :OLD.mgr, :OLD.hiredate, :OLD.sal, :OLD.comm, :OLD.deptno);
END;
/

(OR)

CREATE OR REPLACE TRIGGER trig_emp_table
AFTER DELETE ON EMP
FOR EACH ROW
BEGIN
INSERT INTO emp_trigger_table (empno, ename, job, mgr, hiredate, sal, comm, deptno)
VALUES (:New.empno, :New.ename, :New.job, :New.mgr, :New.hiredate, :New.sal, :New.comm, :New.deptno);
END;
/

SQL SERVER:
------------------
CREATE TRIGGER trigger_name
ON table_name
AFTER INSERT
AS
BEGIN
-- Trigger logic here
INSERT INTO audit_table(user_name, action_date)
SELECT SYSTEM_USER, GETDATE();
END;

Program:
-----------
CREATE TRIGGER trig_emp_table
ON EMP
AFTER DELETE
AS
BEGIN
INSERT INTO emp_trigger_table (empno, ename, job, mgr, hiredate, sal, comm, deptno)
SELECT empno, ename, job, mgr, hiredate, sal, comm, deptno
FROM deleted;
END;

(OR)

CREATE OR ALTER TRIGGER trig_emp_table
ON EMP
AFTER INSERT
AS
BEGIN
INSERT INTO emp_trigger_table (empno, ename, job, mgr, hiredate, sal, comm, deptno)
SELECT empno, ename, job, mgr, hiredate, sal, comm, deptno   
FROM inserted;
END;

In SQL Server, `deleted` is a special, system-generated table, not a real user-defined table. It's automatically available inside DML triggers to let you access the "before" values of the rows affected by a `DELETE` or `UPDATE`.

SQL Server uses relational concepts, and internally, during a trigger execution, it creates two virtual tables:

 Pseudo-table | Used in                            | Contains                         
 -------------- -----------          -----------
 `deleted`        | `DELETE`, `UPDATE`  | The old (pre-change) row values  
 `inserted`       | `INSERT`, `UPDATE`   | The new (post-change) row values 

These act like temporary tables and can be queried using normal SQL syntax like:

SELECT * FROM deleted;
Or joined with actual tables if needed:

SELECT d.empno, e.ename
FROM deleted d
JOIN other_table e ON d.empno = e.empno;

Suppose this statement runs:
DELETE FROM emp WHERE empno = 7369;
Then inside your trigger, the `deleted` table will contain just one row: the one with `empno = 7369`.

In Oracle, `:OLD` is a bind variable used in row-level triggers to refer to the previous (old) values of a row before it was modified or deleted.

* `:OLD` is a record that holds the column values before the triggering DML operation (`UPDATE` or `DELETE`).
* It’s only available in row-level triggers, not statement-level ones.
* You must specify `FOR EACH ROW` in the trigger for `:OLD` to work.

Behavior by DML Type:
 Trigger Type | `:OLD` Available? | `:NEW` Available? | Description  
 ----------------    ----------------------    ----------------------    --------------
 `INSERT`     | NO                          | Yes                         | Only new values exist        
 `UPDATE`   | Yes                          | Yes                         | Both old and new values exist
 `DELETE`   | Yes                          | No                          | Only old values exist        

Example: `AFTER UPDATE` Trigger

CREATE OR REPLACE TRIGGER trg_audit_emp
AFTER UPDATE ON emp
FOR EACH ROW
BEGIN
  INSERT INTO emp_audit (empno, old_sal, new_sal)
  VALUES (:OLD.empno, :OLD.sal, :NEW.sal);
END;
/

Note:
-----
* :OLD.sal is the employee's salary before the update.
* :NEW.sal is the updated salary
* You cannot modify :OLD—it's read-only.
* In contrast, :NEW can be written to in `BEFORE INSERT` or `BEFORE UPDATE` triggers.

Oracle and SQL Server stored procedures differences

There are syntactical and functional differences between Oracle and SQL Server when it comes to writing stored procedures. 

Both use different procedural languages:
Oracle uses PL/SQL (Procedural Language/SQL)
SQL Server uses T-SQL (Transact-SQL)

Here's a comparison highlighting key syntactical differences:

1. Procedure Declaration

Oracle:
-------

CREATE OR REPLACE PROCEDURE proc_name (
 p_id IN NUMBER,
p_name OUT VARCHAR2
)
AS
BEGIN
-- PL/SQL block
END;

SQL Server:
-----------
CREATE PROCEDURE proc_name
@id INT,
@name NVARCHAR(100) OUTPUT
AS
BEGIN
-- T-SQL block
END;

2. Variable Declaration

Oracle:
-------
DECLARE
v_total NUMBER;

SQL Server:
----------- DECLARE @total INT;

3. Calling a Stored Procedure with Output Parameters

Oracle:
-------
DECLARE
v_name VARCHAR2(100);
BEGIN
proc_name(101, v_name);
DBMS_OUTPUT.PUT_LINE(v_name);
END;

SQL Server:
----------- DECLARE @name NVARCHAR(100);
EXEC proc_name @id = 101, @name = @name OUTPUT;
PRINT @name;

4. Exception Handling

Oracle:
-------
BEGIN
-- statements
EXCEPTION
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE('Error');
END;

SQL Server:
-----------
BEGIN TRY
-- statements
END TRY
BEGIN CATCH
PRINT 'Error';
END CATCH

STORED PROCEDURES: ----------------------------------

* Write a program to get department-wise salaries.

SQL:

Create or Alter procedure proc_depwise_salaries
@in_deptno int
AS
Begin
Select sal from emp where deptno=@in_deptno;
end;

Execute proc_depwise_salaries @in_deptno=10

ORACLE:

Create or replace Procedure Get_deptwises_sal (
input_deptno IN NUMBER )
AS
BEGIN
select * from emp where deptno=in_deptno;
end;

BEGIN
Get_deptwises_sal(10);
END;
/

Declaring Parameters in Stored Procedures:
-----------------------------------------------------
When you define input and output parameters for a stored procedure in SQL Server, you do not use the DECLARE keyword.

Example:
------------
CREATE PROCEDURE GetDeptSalaryStats
    @inputDeptNo INT,                 -- Input parameter
    @totalSalary DECIMAL(18,2) OUTPUT, -- Output parameter
    @averageSalary DECIMAL(18,2) OUTPUT -- Output parameter
AS
BEGIN
    -- No need to DECLARE again, these are already declared as parameters
    SELECT 
        @totalSalary = SUM(sal),
        @averageSalary = AVG(sal)
    FROM emp
    WHERE deptno = @inputDeptNo;
END;

Note:
-------
* @inputDeptNo, @totalSalary, and @averageSalary are parameters, not local variables.
* When parameters are declared in the procedure header, DECLARE is not used.
* You can use them directly inside the body of the procedure.

You use DECLARE only inside the procedure body or script to declare local variables, like this:
DECLARE @x INT = 10;
This is not a parameter but a local variable, usable only in that block or batch.

| Usage Context               | Syntax Example                                 | Uses DECLARE?      | Scope             

| -------------------------     | -----------------------------------             | -------------                 | ----------------- 

| Procedure parameters   | @deptno INT, @totSal DECIMAL OUTPUT | No            | Across procedure  

| Local variable               | DECLARE @x INT = 5;                     | Yes                        | Inside procedure  

| Ad-hoc script variable  | DECLARE @deptno INT = 10;           | Yes                        | In script/session