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Add new FAQ information.

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Martijn van Oosterhout
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Bruce Momjian
2005-08-10 19:30:05 +00:00
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Frequently Asked Questions (FAQ) for PostgreSQL
Last updated: Fri Jul 29 10:05:09 EDT 2005
Last updated: Wed Aug 10 15:29:42 EDT 2005
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
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4.19) Why do I get "relation with OID ##### does not exist" errors
when accessing temporary tables in PL/PgSQL functions?
4.20) What replication solutions are available?
4.21) Why are my table and column names not recognized in my query?
_________________________________________________________________
General Questions
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The maximum table size and maximum number of columns can be quadrupled
by increasing the default block size to 32k.
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 using another column that is an
MD5 hash of the long column, and full text indexing allows for
searching of words within the column.
4.5) How much database disk space is required to store data from a typical
text file?
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expresssion 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
upper and lowercase characters, it can not have identical values that
differ only in case. To force a particular case to be stored in the
column, use a CHECK constraint or a trigger.
4.9) In a query, how do I detect if a field is NULL? How can I sort on
whether a field is NULL or not?
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There are also commercial and hardware-based replication solutions
available supporting a variety of replication models.
4.20) Why are my table and column names not recognized in my query?
The most common cause is the use of double-quotes around table or
column names during table creation. When double-quotes are used, table
and column names (called identifiers) are stored case-sensitive,
meaning you must use double-quotes when referencing the names in a
query. Some interfaces, like pgAdmin, automatically double-quote
identifiers during table creation. So, for identifiers to be
recognized, you must either:
* Avoid double-quoting identifiers when creating tables
* Use only lowercase characters in identifiers
* Double-quote identifiers when referencing them in queries