Firebird 2.1 Language Reference Update

DML statements
• Only non-negative whole number literals are interpreted as column positions. A whole number resulting from
an expression evaluation or parameter substitution is seen as an integer invariable and will lead to a dummy
sort, since its value is the same for each row.
NULLs placement
Changed in: 1.5, 2.0
Description: Firebird 1.5 has introduced the per-column NULLS FIRST and NULLS LAST directives to specify
where NULLs appear in the sorted column. Firebird 2.0 has changed the default placement of NULLs.
Unless overridden by NULLS FIRST or NULLS LAST, NULLs in ordered columns are placed as follows:
• In Firebird 1.0 and 1.5: at the end of the sort, regardless whether the order is ascending or descending.
• In Firebird 2.0 and up: at the start of ascending orderings and at the end of descending orderings.
See also the table below for an overview of the different versions.
Table 6.1. NULLs placement in ordered columns
Ordering
79
NULLs placement
Firebird 1 Firebird 1.5 Firebird 2
order by Field [asc] bottom bottom top
order by Field desc bottom bottom bottom
order by Field [asc | desc] nulls first — top top
order by Field [asc | desc] nulls last — bottom bottom
Examples:
Notes
• Pre-existing databases may need a backup-restore cycle before they show the correct NULL ordering behaviour
under Firebird 2.0 and up.
• No index will be used on columns for which a non-default NULLS placement is chosen. In Firebird 1.5, that
is the case with NULLS FIRST. In 2.0 and higher, with NULLS LAST on ascending and NULLS FIRST on
descending sorts.
select * from msg
order by process_time desc nulls first
select * from document
order by strlen(description) desc
rows 10
select doc_number, doc_date from payorder
union all
select doc_number, doc_date from budgorder
order by 2 desc nulls last, 1 asc nulls first