-
+
Data Definition
is fixed, and each column has a name. The number of rows is
variable — it reflects how much data is stored at a given moment.
SQL does not make any guarantees about the order of the rows in a
- table. When a table is read, the rows will appear in random order,
+ table. When a table is read, the rows will appear in an unspecified order,
unless sorting is explicitly requested. This is covered in
linkend="queries">. Furthermore, SQL does not assign unique
identifiers to rows, so it is possible to have several completely
-
+
Full Text Search
(
PostgreSQL does this automatically when needed.)
GiST indexes are lossy because each document is represented in the
index by a fixed-length signature. The signature is generated by hashing
- each word into a random bit in an n-bit string, with all these bits OR-ed
+ each word into a single bit in an n-bit string, with all these bits OR-ed
together to produce an n-bit document signature. When two words hash to
the same bit position there will be a false match. If all words in
the query have matches (real or false) then the table row must be