sql server语言 - 查找一个值是否已经存在于表中

Question

我有一个列作为Company_Location表名中的LOCATION CODE我想知道，如果用户输入Location_Code它不应该已经存在于表

Answer 1

可以这样写:

IF NOT EXISTS(
              SELECT NULL FROM Company_Location 
              WHERE Company_Location.[LOCATION CODE]=<Some value>)
BEGIN
    INSERT INTO Company_Location([LOCATION CODE])VALUES(<Some value>)
END

Answer 2

    if exists (select Location_code from Company_Location where Location_code=<something>
begin
    ...Do something here!!
end
else 
PRINT 'records already exist'

Answer 3

可能

SELECT case when [LOCATION CODE] IS NOT NULL then 'Yes'  else 'No' end
FROM Company_Location
WHERE companyID = <value>