问题
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.
回答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.
回答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
回答3:
I would need to see output, but I am assuming, some ID is stored as int and it is being counted, so you should use
SELECT Cast(CID as Varchar(50)) + '-' + Cast(RID as Varchar(50)) + '-'+ Cast(CGID as Varchar(50)) As [IdCombination]
来源：https://stackoverflow.com/questions/38328695/concate-primary-keys-in-sql