在PL/SQL中，過程（procedure）與函數（function）的核心區(qū)別在于用途和返回值：1. 過程用于執(zhí)行操作，不強制返回值，但可通過OUT參數返回多個值；2. 函數用于計算并返回單個值，常用于表達式或SQL語句中；例如，update_salary過程可執(zhí)行更新操作，而get_bonus函數則返回計算出的獎金數額；過程適用于數據修改和多輸出場景，函數適用于需嵌入SQL中的計算邏輯；此外，函數可在過程中調用，但過程不可直接在SQL語句中調用。

In PL/SQL, the main difference between a procedure and a function comes down to their purpose and how they're used. Procedures are meant for performing actions, while functions are designed to compute and return a value.

What a Procedure Does

A procedure is like a small program that does something—like inserting data, updating records, or performing a series of SQL operations. It doesn’t have to return anything, although it can use OUT parameters to send values back.

For example:

CREATE OR REPLACE PROCEDURE update_salary (emp_id IN NUMBER) IS
BEGIN
   UPDATE employees
   SET salary = salary * 1.1
   WHERE employee_id = emp_id;
END;

You'd call this with:

EXEC update_salary(101);

• Procedures are good when you don't need a direct return value.
• They can modify data or perform logic without needing to give something back immediately.
• You can use them in anonymous blocks or call them from other procedures.

How a Function Is Different

A function, on the other hand, must return a value. That makes it useful in expressions or SQL statements where a value is expected.

Here's a basic function:

CREATE OR REPLACE FUNCTION get_bonus (emp_id IN NUMBER) RETURN NUMBER IS
   bonus_amt NUMBER;
BEGIN
   SELECT salary * 0.1 INTO bonus_amt
   FROM employees
   WHERE employee_id = emp_id;

   RETURN bonus_amt;
END;

And you’d use it like this:

SELECT get_bonus(101) FROM dual;

• Functions are ideal when you need to calculate and return a result.
• They’re often used inside SQL queries or assignments.
• Be careful: if your function has DML (like INSERT or UPDATE), you might run into issues using it directly in SQL unless you define it with PRAGMA AUTONOMOUS_TRANSACTION or allow side effects.

When to Use Which

Use a procedure when:

• You're doing an action rather than calculating a value.
• You want to change data (like inserts, updates, deletes).
• You need multiple outputs via OUT parameters.

Use a function when:

• You need to return a single value for use elsewhere.
• You plan to call it inside a SQL query or expression.
• The logic is more about transformation or calculation than modification.

Also keep in mind:

• Functions can be called from within procedures.
• Procedures can't be directly called from a SQL statement unless wrapped in a function or used via a ref cursor.

So, basically:

• Procedures do things, optionally returning values through OUT parameters.
• Functions return a value, and are usually used where a computed result is needed.

That’s the core distinction — not too complicated once you see how each fits into real usage.

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