在SQL中串联主键

Question

I want to concate Primary Keys of multiple tables in SQL directly. I used below query to concate three primary keys with a hyphen between them but the SQL skipped the hyphen and sum up the primary keys and result in a single value.

  SELECT CID + '-' + RID + '-'+  CGID As [IdCombination] ...    

where CID , RID and CGID are the Primary Keys of three SQL Tables.

How it skipped the string part in query ?

Any help would be highly appreciated.

Updated

For Example : The Values of CID , RID and CGID are 3 , 4, 3 respectively. It should be 3-4-3 but the result is 10.

Answer 1

What is happening? Remember that + means both addition and string concatenation. It so happens that - can be interpreted as a number (like -0 ), so SQL Server prefers to interpret the + as addition.

Normally, when you do this type of operation, the separation character cannot be interpreted as a number, and you just get an error. I am amused that you don't get an error in this case.

One method is to explicitly cast the values as strings:

SELECT CAST(CID as VARCHAR(255)) + '-' + CAST(RID +  as VARCHAR(255)) '-'+  CAST(CGID  as VARCHAR(255)) As [IdCombination] 

In SQL Server 2012+, you can do this more simply using CONCAT() :

SELECT CONCAT(CID, '-', RID, '-', 'CGID) As [IdCombination] 

CONCAT() knows that everything should be a string.

Answer 2

Try this

SELECT 5 + '-' +  8

The output is 13. I must admit, that I did not expect this...

And now try this

SELECT CAST('-' AS INT)

The result is 0. As your select starts with an INT, SQL Server tries to do a summa of int values. As the single hyphen is casteable to int implicitly, this returns the summa of your values...

The solution, as pointed out by others is either a cast of your column values to a string type or the usage of CONCAT

Answer 3

我将需要查看输出，但是我假设一些ID以int形式存储并且正在计算中，因此您应该使用

SELECT Cast(CID as Varchar(50)) + '-' + Cast(RID as Varchar(50)) + '-'+  Cast(CGID as Varchar(50)) As [IdCombination]