DROP TABLE
IF
EXISTS emp;
CREATE TABLE emp (
id INT PRIMARY KEY,
enam VARCHAR ( 50 ) UNIQUE,
joindate date NOT NULL,
salary DOUBLE ( 7, 2 ) NOT NULL,
bonus DOUBLE ( 7, 2 ) DEFAULT 0
);
ALTER TABLE emp DROP PRIMARY KEY;
运行后出现 > 1091 - Can't DROP 'PRIMARY'; check that column/key exists 怎么解决