sql - Conversion failed when converting date and/or time from character string month(),year() -

i have these data:

col1             col2  col3 2014-12-31        q      2014-12-10        q   create table persons (     col1 varchar(50),     col2 varchar(50),     col3 varchar(20) );   insert persons(col1, col2,col3)  values ('2014-12-20', 'q','');  insert persons(col1, col2,col3)  values ('2014-12-10', 'q',''); 

i run query:

select    convert(date, col1,104) col1,   col2,   case when col2 = 'q' convert(nvarchar(10),year(col1)+'q0')   end col3 persons 

i error:

conversion failed when converting date and/or time character string

declare  @p table (      col1 varchar(50),     col2 varchar(50),     col3 varchar(20) )     insert @p(col1, col2,col3)       values ('2014-12-20', 'q','');    insert @p(col1, col2,col3)       values ('2014-12-10', 'q','');  select    convert(varchar(10), col1,104) col1,   col2,   case when col2 = 'q'     right(convert(nvarchar(10),year(col1),106),5) + 'q0'   end col3     @p 

output: