Question

//我的代码应该是这样的

CREATE PROCEDURE REGISTRATION
@USERNAME VARCHAR(20)
AS
BEGIN
BEGIN IF
SELECT USERNAME FROM USERS WHERE USERNAME =  @USERNAME 
PRINT 'USER ALREADY EXITS'
ELSE
IF @USERNAME = 'NULL'
PRINT 'Fill username'
end
end

Answer 1

试试这个：

CREATE PROCEDURE REGISTRATION
@USERNAME VARCHAR(20)
AS
BEGIN
declare @count as int
select @count = COUNT(*) from USER where USERNAME =@USERNAME
if(@count > 0)
print 'USER ALREADY EXITS'  -- Record Exists
else
print 'Fill username'  -- NULL
end

Answer 2

使用存在。此外，格式被忽略并且很重要

CREATE PROCEDURE REGISTRATION
@USERNAME VARCHAR(20)=''
AS
BEGIN
    IF exists(SELECT 1 FROM USERS WHERE USERNAME =  @USERNAME)
        begin
            PRINT 'USER ALREADY EXITS'
        end
    ELSE
        begin
            PRINT 'Fill username'
        end
end

如果表中已有名称，则打印错误

2 个答案: