Sql server using a built int function in a stored procedure - sql

Question

I am trying to write a SP that uses the substring function inside a stored procedure where I use the column name as input. However when I run
exec sp_addCountySchoolDistrict N'table', N'districtCountySchoolCode'
It uses the 'districtCountySchoolCode' for the substring and not the value from the row...
For example
create table [dbo].[test] (districtCountySchoolCode nvarchar(100))
insert into dbo.test values ('1234567891234')
go
CREATE PROCEDURE sp_addCountySchoolDistrict
#tableName nvarchar(100),
#colName nvarchar(100)
AS
BEGIN
SET NOCOUNT ON;
DECLARE #Sql NVARCHAR(MAX);
SET #Sql= N'alter table ' + replace(replace(quotename(#tableName),']',''),'[','') +
N' add countyCode as ''' + substring(#colName, 1,2) + N',
districtCode as ''' + substring(#colName, 3,5) + N',
schoolCode as ''' + substring(#colName, 8,7) + N';'
select #sql;
EXECUTE sp_executesql #Sql
END
GO
exec sp_addCountySchoolDistrict N'[dbo].[test]', N'districtCountySchoolCode'
select * from test_copy
Coder Wall

Answer 1

Put the substring in the literal part of the dynamic sql, like this:
N' add countyCode as substring(''' + #colName+ N', 1,2) ,

Answer 2

try this
exec sp_addCountySchoolDistrict N'[dbo].[test]', N'1234567891234'

Answer 3

Your mistake is that you pass the "column name" as a string but your code nowhere selects the value from test table for the specified column. You have to perform a select statement first, to get the value and then use the value in the rest code.
This should work
create table [dbo].[test] (districtCountySchoolCode nvarchar(100))
insert into dbo.test values ('1234567891234')
go
CREATE PROCEDURE sp_addCountySchoolDistrict
#tableName nvarchar(100),
#colName nvarchar(100)
AS
BEGIN
declare #val nvarchar(100);
declare #initialQuery nvarchar(100);
SET NOCOUNT ON;
DECLARE #Sql NVARCHAR(MAX);
SET #initialQuery = 'SELECT #value=' + quotename(#colName) + ' FROM ' + replace(replace(quotename(#tableName),']',''),'[','')
EXECUTE sp_executesql #initialQuery, N'#value nvarchar(100) OUTPUT', #value=#val OUTPUT
SET #Sql= N'alter table ' + replace(replace(quotename(#tableName),']',''),'[','') +
N' add countyCode as ''' + substring(#val, 1,2) + N''',
districtCode as ''' + substring(#val, 3,5) + N''',
schoolCode as ''' + substring(#val, 8,7) + N''';'
select #sql;
EXECUTE sp_executesql #Sql
END
GO
exec sp_addCountySchoolDistrict N'[dbo].[test]', N'districtCountySchoolCode'
select * from test
But you have to add a where condition i suppose if you have more than one values in test table.