mysql儲存過程中，IN用來輸入引數，OUT用來輸出引數，INOUT輸入和輸出。

1. IN引數
   建立儲存過程

mysql> delimiter //
mysql> create procedure proce1(IN count int)
    -> begin
    -> select count;
    -> set count = 2;
    -> select count;
    -> end
    -> //

執行儲存過程

mysql> set @count = 1//
Query OK,
 
 0 rows affected (0.00 sec)

mysql> call proce1(@count)//
+-------+
| count |
+-------+
|     1 |
+-------+
1 row in set (0.00 sec)

+-------+
| count |
+-------+
|     2 |
+-------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

mysql> select @count
    -> //
+--------+
| @count |
+--------+
 

|      1 |
+--------+
1 row in set (0.00 sec)

mysql> 

在上面儲存過程中，我們定義了一個引數@count，賦值為1，傳入到儲存過程中，在儲存過程中賦值為2，當儲存過程結束後，列印@count的值依舊是1.

2. OUT引數
   建立儲存過程

mysql> create procedure proce_out(OUT count int)
    -> begin
    -> select count;
    -> set count = 2;
    -> select count;
    -
 
> end//
Query OK, 0 rows affected (0.05 sec)

執行儲存過程

mysql> set @count=1;
    -> call proce_out(@count);
    -> select @count;
    -> //
Query OK, 0 rows affected (0.00 sec)

+-------+
| count |
+-------+
|  NULL |
+-------+
1 row in set (0.00 sec)

+-------+
| count |
+-------+
|     2 |
+-------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

+--------+
| @count |
+--------+
|      2 |
+--------+
1 row in set (0.00 sec)

mysql> 

@count在外面賦值為1，因為引數是OUT型別，所以儲存過程中打印出來為null，儲存過程中賦值為2，儲存過程結束，檢視@count的值，依舊為2。

3. INOUT 輸入輸出引數
   建立儲存過程

mysql> create procedure proce_inout(INOUT count int)
    -> begin
    -> select count;
    -> set count = 2;
    -> select count;
    -> end;
    -> //

執行儲存過程

mysql> set @count = 1;
    -> call proce_inout(@count);
    -> select @count;
    -> //
Query OK, 0 rows affected (0.00 sec)

+-------+
| count |
+-------+
|     1 |
+-------+
1 row in set (0.00 sec)

+-------+
| count |
+-------+
|     2 |
+-------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

+--------+
| @count |
+--------+
|      2 |
+--------+
1 row in set (0.00 sec)

我們在外面把@count賦值為1，儲存過程裡面獲取到了值，然後賦值為2，儲存過程結束後，打印出來的值依舊是2