The scope of a local variable is the BEGIN ... END block within which it is declared. 局部变量的作用域是在其中声明的BEGIN ... END块。The variable can be referred to in blocks nested within the declaring block, except those blocks that declare a variable with the same name.可以在嵌套在声明块中的块中引用变量，但声明具有相同名称的变量的块除外。

Because local variables are in scope only during stored program execution, references to them are not permitted in prepared statements created within a stored program. 由于局部变量仅在存储程序执行期间在作用域中，因此在存储程序中创建的准备语句中不允许引用它们。Prepared statement scope is the current session, not the stored program, so the statement could be executed after the program ends, at which point the variables would no longer be in scope. Prepared语句作用域是当前会话，而不是存储程序，因此语句可以在程序结束后执行，此时变量将不再在作用域中。For example, SELECT ... INTO local_var cannot be used as a prepared statement. 例如，SELECT ... INTO local_var不能用作准备语句。This restriction also applies to stored procedure and function parameters. 此限制也适用于存储过程和函数参数。See Section 13.5.1, “PREPARE Statement”.请参阅第13.5.1节，“PREPARE语句”。

A local variable should not have the same name as a table column. 局部变量不应与表列同名。If an SQL statement, such as a SELECT ... INTO statement, contains a reference to a column and a declared local variable with the same name, MySQL currently interprets the reference as the name of a variable. 如果SQL语句，例如SELECT ... INTO语句，包含对列的引用和声明的同名局部变量，MySQL当前将引用解释为变量的名称。Consider the following procedure definition:考虑下面的过程定义：

CREATE PROCEDURE sp1 (x VARCHAR(5))
BEGIN
  DECLARE xname VARCHAR(5) DEFAULT 'bob';
  DECLARE newname VARCHAR(5);
  DECLARE xid INT;

  SELECT xname, id INTO newname, xid
    FROM table1 WHERE xname = xname;
  SELECT newname;
END;

MySQL interprets xname in the SELECT statement as a reference to the xname variable rather than the xname column. MySQL将SELECT语句中的xname解释为对xname变量的引用，而不是对xname列的引用。Consequently, when the procedure sp1()is called, the newname variable returns the value 'bob' regardless of the value of the table1.xname column.因此，当调用过程sp1()时，newname变量返回值'bob'，而不管table1.xname列的值是多少。

Similarly, the cursor definition in the following procedure contains a SELECT statement that refers to xname. 类似地，以下过程中的游标定义包含引用xname的SELECT语句。MySQL interprets this as a reference to the variable of that name rather than a column reference.MySQL将其解释为对该名称的变量的引用，而不是列引用。

CREATE PROCEDURE sp2 (x VARCHAR(5))
BEGIN
  DECLARE xname VARCHAR(5) DEFAULT 'bob';
  DECLARE newname VARCHAR(5);
  DECLARE xid INT;
  DECLARE done TINYINT DEFAULT 0;
  DECLARE cur1 CURSOR FOR SELECT xname, id FROM table1;
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;

  OPEN cur1;
  read_loop: LOOP
    FETCH FROM cur1 INTO newname, xid;
    IF done THEN LEAVE read_loop; END IF;
    SELECT newname;
  END LOOP;
  CLOSE cur1;
END;

See also Section 25.8, “Restrictions on Stored Programs”.另请参见第25.8节，“存储程序的限制”。