**1. 語法** ```sql IF condition THEN statement_list [ELSEIF condition THEN statement_list] [ELSE statement_list] END IF; - condition：條件成立則執行 statement_list 語句 ``` **2. 案例演示** ```sql # 1. 數據準備 drop table if exists account; create table account ( `id` int(11) primary key auto_increment not null, `username` varchar(255) not null, `password` varchar(255) not null ); insert into account values(1, '張三', 'zhangsan'); insert into account values(2, '李四', 'lisi'); # 2. 在存儲過程中使用 IF 語句 delimiter $ create procedure proce_account01(in id_ int, in uname varchar(255), in pass varchar(255)) begin if id_ = 1 then update account set username=uname, password=pass where id=id_; elseif id_ = 2 then delete from account where id=id_; else insert into account(id_, uname, pass); end if; end $ # 3. 調用存儲過程 call proce_account01(3, '王五', 'wangwu') $ # 4. 查看結果 mysql> select * from account $ +----+----------+----------+ | id | username | password | +----+----------+----------+ | 1 | 張三 | zhangsan | | 2 | 李四 | lisi | | 3 | 王五 | wangwu | +----+----------+----------+ ```