Frequently Asked Questions (FAQ) for PostgreSQL
- Last updated: Sat Jun 3 20:17:01 EDT 2006
+ Last updated: Wed Jun 7 17:22:48 EDT 2006
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
One limitation is that indexes can not be created on columns longer
than about 2,000 characters. Fortunately, such indexes are rarely
- needed. Uniqueness is best guaranteed by a funtion index of an MD5
+ needed. Uniqueness is best guaranteed by a function index of an MD5
hash of the long column, and full text indexing allows for searching
of words within the column.
FROM tab
WHERE lower(col) = 'abc';
- This will not use an standard index. However, if you create a
- expresssion index, it will be used:
+ This will not use an standard index. However, if you create an
+ expression index, it will be used:
CREATE INDEX tabindex ON tab (lower(col));
If the above index is created as UNIQUE, though the column can store
4.12) What is an OID? What is a CTID?
Every row that is created in PostgreSQL gets a unique OID unless
- created WITHOUT OIDS. OIDs are autotomatically assigned unique 4-byte
+ created WITHOUT OIDS. OIDs are automatically assigned unique 4-byte
integers that are unique across the entire installation. However, they
overflow at 4 billion, and then the OIDs start being duplicated.
PostgreSQL uses OIDs to link its internal system tables together.
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<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
- <P>Last updated: Sat Jun 3 20:17:01 EDT 2006</P>
+ <P>Last updated: Wed Jun 7 17:22:48 EDT 2006</P>
<P>Current maintainer: Bruce Momjian (<A href=
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)
<P>One limitation is that indexes can not be created on columns
longer than about 2,000 characters. Fortunately, such indexes are
- rarely needed. Uniqueness is best guaranteed by a funtion index
+ rarely needed. Uniqueness is best guaranteed by a function index
of an MD5 hash of the long column, and full text indexing
allows for searching of words within the column.</P>
FROM tab
WHERE lower(col) = 'abc';
</PRE>
- This will not use an standard index. However, if you create a
- expresssion index, it will be used:
+ This will not use an standard index. However, if you create an
+ expression index, it will be used:
<PRE>
CREATE INDEX tabindex ON tab (lower(col));
</PRE>
<P>Every row that is created in PostgreSQL gets a unique
<SMALL>OID</SMALL> unless created <SMALL>WITHOUT OIDS</SMALL>.
- O<SMALL>ID</SMALL>s are autotomatically assigned unique 4-byte
+ O<SMALL>ID</SMALL>s are automatically assigned unique 4-byte
integers that are unique across the entire installation. However,
they overflow at 4 billion, and then the O<SMALL>ID</SMALL>s start
being duplicated. PostgreSQL uses <SMALL>OID</SMALL>s to link its