错误1022：无法在MySQL中写入重复键错误

Question

我得到了：

Error code 1022: Can't write; duplicate key in table 'eventrequest'

但我不知道为什么。请帮忙。谢谢。下面是我的MySQL创建语句。

CREATE TABLE EventRequest
( EventNo VARCHAR(8) NOT NULL,
DateHeld DATE NOT NULL,
DateReq DATE NOT NULL,
FacNo VARCHAR(8) NOT NULL,
CustNo VARCHAR(8) NOT NULL,
DateAuth DATE,
Status ENUM('Approved', 'Denied', 'Pending'),
EstCost DECIMAL(15,2) NOT NULL,
EstAudience INT NOT NULL,
BudNo VARCHAR(8), 
CONSTRAINT PK_EVENTNO PRIMARY KEY (EventNo), 
CONSTRAINT FK_CUSTNO FOREIGN KEY (CustNo) REFERENCES Customer (CustNo),
CONSTRAINT FK_FACNO FOREIGN KEY (FacNo) REFERENCES Facility (FacNo),
CHECK(EstAudience > 0 ) );