LIMIT and OFFSET allow you to retrieve just
a portion of the rows that are generated by the rest of the query:
SELECT select_list
FROM table_expression
[LIMIT { number | ALL }] [OFFSET number]
If a limit count is given, no more than that many rows will be
returned (but possibly less, if the query itself yields less rows).
LIMIT ALL is the same as omitting the LIMIT
clause.
OFFSET says to skip that many rows before beginning to
return rows to the client. OFFSET 0 is the same as
omitting the OFFSET clause. If both OFFSET
and LIMIT appear, then OFFSET rows are
skipped before starting to count the LIMIT rows that
are returned.
When using LIMIT, it is a good idea to use an
ORDER BY clause that constrains the result rows into a
unique order. Otherwise you will get an unpredictable subset of
the query's rows---you may be asking for the tenth through
twentieth rows, but tenth through twentieth in what ordering? The
ordering is unknown, unless you specified ORDER BY.
The query optimizer takes LIMIT into account when
generating a query plan, so you are very likely to get different
plans (yielding different row orders) depending on what you give
for LIMIT and OFFSET. Thus, using
different LIMIT/OFFSET values to select
different subsets of a query result will give
inconsistent results unless you enforce a predictable
result ordering with ORDER BY. This is not a bug; it
is an inherent consequence of the fact that SQL does not promise to
deliver the results of a query in any particular order unless
ORDER BY is used to constrain the order.
