anchor.diff:  --------------------------------------------------
   *Input*:
   
  -<1> string expression
  +<1> string expression. If `null`, the function returns `null`.
   
   *Output*: string
   
  
positive.code: 
  *Output*: string
  
  *Description*: Returns a character string that is the result of concatenating `string_exp1` to `string_exp2`. `NULL` input strings are treated as empty strings.
  
  [source, sql]
  --------------------------------------------------
  
negative.code: --------------------------------------------------
  *Input*:
  
  <1> integer expression. If `null` or negative, the function returns `null`.
  
  *Output*: string
  
  