《MySQL必知必会》[05] 存储过程和游标

--创建存储过程
CREATE PROCEDURE <存储过程的名称>(<变量的类型定义>)
BEGIN
  <执行操作>
END;
--执行存储过程
CALL <存储过程的名称>(<@变量名>);
--删除存储过程
DROP PROCEDURE <存储过程的名称>;

-- Name: ordertotal
-- Parameters: onumber = order number
--             taxable = 0 if not taxable, 1 if taxable
--             ototal  = order total variable
CREATE PROCEDURE ordertotal(
  IN  onumber INT,
  IN  taxable BOOLEAN,
  OUT ototal DECIMAL(8, 2)
) COMMENT ‘Obtain order total, optionally adding tax‘
BEGIN
  --Declare variable for total
  DECLARE total DECIMAL(8, 2);
  --Declare tax percentage
  DECLARE taxrate INT DEFAULT 6;
  
  --GET the order total
  SELECT Sum(item_price*quantity)
  FROM orderitems
  WHERE order_num = onumber
  INTO total;
  --Is this taxable
  IF taxable THEN
    SELECT total+(total/100*taxrate) INTO total;
  END IF;
  SELECT total INTO ototal;
END;

CREATE PROCEDURE ordertotal(
  IN  onumber INT,
  IN  taxable BOOLEAN,
  OUT ototal DECIMAL(8, 2)
) COMMENT ‘Obtain order total, optionally adding tax‘

BEGIN
  ...
END;

• BEGIN和END用来界定存储过程操作执行的语句

  --Declare variable for total
  DECLARE total DECIMAL(8, 2);
  --Declare tax percentage
  DECLARE taxrate INT DEFAULT 6;
  
  --GET the order total
  SELECT Sum(item_price*quantity)
  FROM orderitems
  WHERE order_num = onumber
  INTO total;

• DECLARE用来定义存储过程中的局部变量
• INTO表示赋值到变量

  --Is this taxable
  IF taxable THEN
    SELECT total+(total/100*taxrate) INTO total;
  END IF;

• IF <boolean> THEN <do something> END IF 为条件执行语句，记得END IF结尾

public void ordertotal(int onumber, boolean taxable, double ototal) {
    double total;
    int taxrate = 6;
    
    total = getOrderTotal(onumber);
    if (taxable) {
        total += total / (100 * taxrate);
    }
    ototal = total;
}

--不含营业税
CALL ordertotal(20005, 0, @total);
SELECT @total
+----------+
|  @total  |
+----------+
|  149.87  |
+----------+
--包含营业税
CALL ordertotal(20005, 1, @total);
SELECT @total
+-----------------+
|      @total     |
+-----------------+
|  158.862200000  |
+-----------------+

SHOW CREATE PROCEDURE ordertotal;

DROP PROCEDURE ordertotal;

CREATE PROCEDURE processorders()
BEGIN
  DECLARE ordernumbers CURSOR
  FOR
  SELECT order_num FROM orders;
END;

CREATE PROCEDURE processorders()
BEGIN
  --Declare
  DECLARE ordernumbers CURSOR
  FOR
  SELECT order_num FROM orders;
  --Open
  OPEN ordernumbers;
  
  --Close
  CLOSE ordernumbers;
END;

CREATE PROCEDURE processorders()
BEGIN
  --Declare
  DECLARE o INT;
  DECLARE ordernumbers CURSOR
  FOR
  SELECT order_num FROM orders;
 
  --Open
  OPEN ordernumbers;
 
  --Get
  FETCH ordernumbers INTO o;  
 
  --Close
  CLOSE ordernumbers;
END;

CREATE PROCEDURE processorders()
BEGIN
  --Declare local variables
  DELCARE done BOOLEAN DEFAULT 0;
  DECLARE o    INT;
  DECLARE t    DECIMAL(8,2);
  --Declare cursor
  DECLARE ordernumbers CURSOR
  FOR
  SELECT order_num FROM orders;
 
  --Declare continue handler
  DECLARE CONTINUE HANDLER FOR SQLSTATE ‘02000‘ SET done=1;
  --Create a table to store the results
  CREATE TABLE IF NOT EXISTS ordertotals(order_num INT, total DECIMAL(8,2));  
  --Open the cursor
  OPEN ordernumbers;
 
  --Loop through all rows
  REPEAT
    FETCH ordernumbers INTO o;
    CALL ordertotal(o, 1, t);
    INSERT INTO ordertotals(order_num, total) VALUES(o, t);
  UNTIL done END REPEAT;
  --Close the cursor
  CLOSE ordernumbers;
END;

• 以上存储过程，游标不断读取订单号，并以此为参调用另一个存储过程，将最终的值填入到表ordertotals中
• CONTINUE HANDLER 是在条件出现时执行的代码，SQLSTATE ‘02000‘ 表没有找到更多的行（MySQL错误代码）
  

SELECT * FROM ordertotals;
+---------+---------+
|  20005  |  158.86 |
|  20006  |   58.30 |
|  20007  | 1060.00 |
|  20008  |  132.50 |
|  20009  |   40.78 |
+---------+---------+