From 0b79ed27457bda0f2545257225923488ca72a453 Mon Sep 17 00:00:00 2001 From: Bruce Momjian Date: Fri, 4 Jan 2002 05:44:45 +0000 Subject: Update FAQ. --- doc/src/FAQ/FAQ.html | 121 +++++++++++++++++++++++---------------------------- 1 file changed, 55 insertions(+), 66 deletions(-) (limited to 'doc/src') diff --git a/doc/src/FAQ/FAQ.html b/doc/src/FAQ/FAQ.html index dd5eb71073a..1133ab77d2f 100644 --- a/doc/src/FAQ/FAQ.html +++ b/doc/src/FAQ/FAQ.html @@ -11,7 +11,7 @@ alink="#0000FF">

Frequently Asked Questions (FAQ) for PostgreSQL

-

Last updated: Wed Dec 5 00:41:12 EST 2001

+

Last updated: Fri Jan 4 00:44:42 EST 2002

Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
@@ -89,57 +89,55 @@

Operational Questions

- 4.1) Why is the system confused about commas, - decimal points, and date formats.
- 4.2) What is the exact difference between + 4.1) What is the difference between binary cursors and normal cursors?
- 4.3) How do I SELECT only the + 4.2) How do I SELECT only the first few rows of a query?
- 4.4) How do I get a list of tables or other + 4.3) How do I get a list of tables or other things I can see in psql?
- 4.5) How do you remove a column from a + 4.4) How do you remove a column from a table?
- 4.6) What is the maximum size for a row, table, + 4.5) What is the maximum size for a row, table, database?
- 4.7) How much database disk space is required + 4.6) How much database disk space is required to store data from a typical text file?
- 4.8) How do I find out what tables or indexes + 4.7) How do I find out what tables or indexes are defined in the database?
- 4.9) My queries are slow or don't make use of + 4.8) My queries are slow or don't make use of the indexes. Why?
- 4.10) How do I see how the query optimizer is + 4.9) How do I see how the query optimizer is evaluating my query?
- 4.11) What is an R-tree index?
- 4.12) What is the Genetic Query Optimizer?
- 4.13) How do I perform regular expression + 4.10) What is an R-tree index?
+ 4.11) What is the Genetic Query Optimizer?
+ 4.12) How do I perform regular expression searches and case-insensitive regular expression searches? How do I use an index for case-insensitive searches?
- 4.14) In a query, how do I detect if a field + 4.13) In a query, how do I detect if a field is NULL?
- 4.15) What is the difference between the + 4.14) What is the difference between the various character types?
- 4.16.1) How do I create a + 4.15.1) How do I create a serial/auto-incrementing field?
- 4.16.2) How do I get the value of a + 4.15.2) How do I get the value of a SERIAL insert?
- 4.16.3) Don't currval() and + 4.15.3) Don't currval() and nextval() lead to a race condition with other users?
- 4.17) What is an OID? What is a + 4.16) What is an OID? What is a TID?
- 4.18) What is the meaning of some of the terms + 4.17) What is the meaning of some of the terms used in PostgreSQL?
- 4.19) Why do I get the error "ERROR: + 4.18) Why do I get the error "ERROR: Memory exhausted in AllocSetAlloc()?"
- 4.20) How do I tell what PostgreSQL version I + 4.19) How do I tell what PostgreSQL version I am running?
- 4.21) My large-object operations get + 4.20) My large-object operations get invalid large obj descriptor. Why?
- 4.22) How do I create a column that will + 4.21) How do I create a column that will default to the current time?
- 4.23) Why are my subqueries using + 4.22) Why are my subqueries using IN so slow?
- 4.24) How do I perform an outer join?
- 4.25) How do I perform queries using multiple databases?
+ 4.23) How do I perform an outer join?
+ 4.24) How do I perform queries using multiple databases?
@@ -788,22 +786,13 @@

Operational Questions

-

4.1) Why is system confused about commas, - decimal points, and date formats.

- -

Check your locale configuration. PostgreSQL uses the locale - setting of the user that ran the postmaster process. There - are postgres and psql SET commands to control the - date format. Set those accordingly for your operating - environment.

- -

4.2) What is the exact difference between +

4.1) What is the difference between binary cursors and normal cursors?

See the DECLARE manual page for a description.

-

4.3) How do I SELECT only the +

4.2) How do I SELECT only the first few rows of a query?

See the FETCH manual page, or use @@ -816,7 +805,7 @@ records requested, or the entire query may have to be evaluated until the desired rows have been generated.

-

4.4) How do I get a list of tables or other +

4.3) How do I get a list of tables or other things I can see in psql?

@@ -827,7 +816,7 @@ -E option so it will print out the queries it uses to execute the commands you give.

-

4.5) How do you remove a column from a +

4.4) How do you remove a column from a table?

We do not support ALTER TABLE DROP COLUMN, but do @@ -840,7 +829,7 @@ ALTER TABLE new_table RENAME TO old_table; -

4.6) What is the maximum size for a row, +

4.5) What is the maximum size for a row, table, database?

These are the limits:

@@ -864,7 +853,7 @@

The maximum table size and maximum number of columns can be increased if the default block size is increased to 32k.

-

4.7) How much database disk space is required +

4.6) How much database disk space is required to store data from a typical text file?

@@ -897,7 +886,7 @@

Indexes do not require as much overhead, but do contain the data that is being indexed, so they can be large also.

-

4.8) How do I find out what tables or indexes +

4.7) How do I find out what tables or indexes are defined in the database?

psql has a variety of backslash commands to show such @@ -907,7 +896,7 @@ illustrates many of the SELECTs needed to get information from the database system tables.

-

4.9) My queries are slow or don't make use of +

4.8) My queries are slow or don't make use of the indexes. Why?

PostgreSQL does not automatically maintain statistics. @@ -937,12 +926,12 @@ ~(regular expression searches) should start with ^.

-

4.10) How do I see how the query optimizer +

4.9) How do I see how the query optimizer is evaluating my query?

See the EXPLAIN manual page.

-

4.11) What is an R-tree index?

+

4.10) What is an R-tree index?

An R-tree index is used for indexing spatial data. A hash index can't handle range searches. A B-tree index only handles range @@ -967,7 +956,7 @@ practice, extending R-trees requires a bit of work and we don't currently have any documentation on how to do it.

-

4.12) What is the Genetic Query +

4.11) What is the Genetic Query Optimizer?

The GEQO module speeds query optimization when @@ -975,7 +964,7 @@ the handling of large join queries through nonexhaustive search.

-

4.13) How do I perform regular expression +

4.12) How do I perform regular expression searches and case-insensitive regular expression searches? How do I use an index for case-insensitive searches?

@@ -999,12 +988,12 @@ CREATE INDEX tabindex on tab (lower(col)); -

4.14) In a query, how do I detect if a field +

4.13) In a query, how do I detect if a field is NULL?

You test the column with IS NULLIS NOT NULL.

-

4.15) What is the difference between the +

4.14) What is the difference between the various character types?

 Type            Internal Name   Notes
@@ -1034,7 +1023,7 @@ BYTEA           bytea           variable-length byte array (null-safe)
     binary data, particularly values that include NULL
     bytes.

     
-    
4.16.1) How do I create a
+    
4.15.1) How do I create a
     serial/auto-incrementing field?

 
     
PostgreSQL supports a SERIAL data type. It
@@ -1064,13 +1053,13 @@ BYTEA           bytea           variable-length byte array (null-safe)
     
Numbering
     Rows.

 
-    
4.16.2) How do I get the value of a
+    
4.15.2) How do I get the value of a
     SERIAL insert?

 
     
One approach is to to retrieve the next SERIAL
     value from the sequence object with the nextval() function
     before inserting and then insert it explicitly. Using the
-    example table in 4.16.1, that might look like
+    example table in 4.15.1, that might look like
     this in Perl:

 
     new_id = output of "SELECT nextval('person_id_seq')"
@@ -1091,20 +1080,20 @@ BYTEA           bytea           variable-length byte array (null-safe)
     INSERT INTO person (name) VALUES ('Blaise Pascal');
     new_id = output of "SELECT currval('person_id_seq')";
 

-    Finally, you could use the OID
+    Finally, you could use the OID
     returned from the INSERT statement to look up the
     default value, though this is probably the least portable approach.
     In Perl, using DBI with Edmund Mergl's DBD::Pg module, the oid
     value is made available via $sth->{pg_oid_status} after
     $sth->execute(). 
 
-    
4.16.3) Don't currval() and
+    
4.15.3) Don't currval() and
     nextval() lead to a race condition with other users?

 
     
No. Currval() returns the current value assigned by your
     backend, not by all users.

 
-    
4.17) What is an OID? What is
+    
4.16) What is an OID? What is
     a TID?

 
     
OIDs are PostgreSQL's answer to unique row ids.
@@ -1149,7 +1138,7 @@ BYTEA           bytea           variable-length byte array (null-safe)
     or reloaded. They are used by index entries to point to physical
     rows.

 
-    
4.18) What is the meaning of some of the
+    
4.17) What is the meaning of some of the
     terms used in PostgreSQL?

 
     
Some of the source code and older documentation use terms that
@@ -1178,7 +1167,7 @@ BYTEA           bytea           variable-length byte array (null-safe)
     
A list of general database terms can be found at: http://www.comptechnews.com/~reaster/dbdesign.html

 
-    
4.19) Why do I get the error "ERROR: 
+    
4.18) Why do I get the error "ERROR: 
      Memory exhausted in AllocSetAlloc()?"

     

 
@@ -1198,13 +1187,13 @@ BYTEA           bytea           variable-length byte array (null-safe)
     backend is returning too much data, try it before starting the
     client. 
 
-    
4.20) How do I tell what PostgreSQL version
+    
4.19) How do I tell what PostgreSQL version
     I am running?

     

 
     
From psql, type select version();

 
-    
4.21) My large-object operations get
+    
4.20) My large-object operations get
     invalid large obj descriptor. Why?

     

 
@@ -1221,7 +1210,7 @@ BYTEA           bytea           variable-length byte array (null-safe)
     
If you are using a client interface like ODBC you
     may need to set auto-commit off.

 
-    
4.22) How do I create a column that will
+    
4.21) How do I create a column that will
     default to the current time?

     

 
@@ -1231,7 +1220,7 @@ BYTEA           bytea           variable-length byte array (null-safe)
-

4.23) Why are my subqueries using +

4.22) Why are my subqueries using IN so slow?

@@ -1254,7 +1243,7 @@ BYTEA bytea variable-length byte array (null-safe) We hope to fix this limitation in a future release. -

4.24) How do I perform an outer join?
+

4.23) How do I perform an outer join?

PostgreSQL 7.1 and later supports outer joins using the SQL @@ -1295,7 +1284,7 @@ BYTEA bytea variable-length byte array (null-safe) ORDER BY col1 -

4.25) How do I perform queries +

4.24) How do I perform queries using multiple databases?

There is no way to query any database except the current one. -- cgit v1.2.3