diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml index 20443f2b28..aee74366b0 100644 --- a/doc/src/sgml/func.sgml +++ b/doc/src/sgml/func.sgml @@ -1,4 +1,4 @@ - + Functions and Operators @@ -8387,8 +8387,8 @@ SELECT xmlagg(x) FROM test; - The influence the order of the concatenation, something like the - following approach to sort the input values can be used: + To determine the order of the concatenation, something like the + following approach can be used: xmlagg, as well as similar user-defined aggregate functions, produce meaningfully different result values depending on the order of the input values. In the current - implementation, the order of the concatenation is in principle - undefined. Making the input values to be sorted in some other way + implementation, the order of the input is in principle unspecified. + Supplying the input values from a sorted subquery will usually work, however. For example: - But this approach is not guaranteed to work in all situations, and - it is not strictly SQL-conforming. A future version of PostgreSQL - might provide an additional feature to control the order in a - better-defined way (xmlagg(expr ORDER BY expr, expr, - ...). + But this syntax is not allowed in the SQL standard, and is + not portable to other database systems. A future version of + PostgreSQL might provide an additional feature to control + the order in a better-defined way (xmlagg(expr ORDER BY expr, expr, + ...)).