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Diffstat (limited to 'doc/FAQ')
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@@ -1,8 +1,8 @@ Frequently Asked Questions (FAQ) for PostgreSQL - Last updated: Thu Sep 4 01:32:22 EDT 1997 - Version: 6.1.1 + Last updated: Sat Sep 13 22:00:02 EDT 1997 + Version: 6.2beta Current maintainer: Bruce Momjian (maillist@candle.pha.pa.us) @@ -90,6 +90,7 @@ Questions answered: 3.21) What is the meaning of some of the terms used in Postgres? 3.22) What is Genetic Query Optimization? 3.23) How do you remove a column from a table? + 3.24) How do SELECT only the first few rows of a query? 4) Questions about extending PostgreSQL @@ -514,24 +515,7 @@ Section 3: PostgreSQL Features 3.6) What is the exact difference between binary cursors and normal cursors? - Normal cursors return data back in ASCII format. Since data is stored - natively in binary format, the system must do a conversion to produce - the ASCII format. In addition, ASCII formats are often large in size - than binary format. Once the attributes come back in ASCII, often the - client application then has to convert it to a binary format to - manipulate it anyway. - - Binary cursors give you back the data in the native binary - representation. Thus, binary cursors will tend to be a little faster - since there's less overhead of conversion. - - However, ASCII is architectural neutral whereas binary representation - can differ between different machine architecture. Thus, if your - client machine uses a different representation than you server - machine, getting back attributes in binary format is probably not what - you want. Also, if your main purpose is displaying the data in ASCII, - then getting it back in ASCII will save you some effort on the client - side. + See the declare manual page for a description. 3.7) What is a R-tree index and what is it used for? @@ -590,24 +574,12 @@ Section 3: PostgreSQL Features 3.10) How do I do regular expression searches? case-insensitive regexp searching? - PostgreSQL supports the SQL LIKE syntax as well as more general - regular expression searching with the ~ operator. The !~ is the - negated regexp operator. ~* and !~* are the case-insensitive regular - expression operators. + See the pgbuiltin manual page. Search for regular expression. 3.11) I experienced a server crash during a vacuum. How do I remove the lock file? - If the server crashes during a vacuum command, chances are it will - leave a lock file hanging around. Attempts to re-run the vacuum - command result in - - - WARN:can't create lock file -- another vacuum cleaner running? - - If you are sure that no vacuum is actually running, you can remove the - file called "pg_vlock" in your database directory (which is - $PGDATA/base/<dbName>) + See the vacuum manual page. 3.12) What is the difference between the various character types? @@ -638,10 +610,8 @@ BYTEA bytea variable-length array of bytes 3.14) How do I see how the query optimizer is evaluating my query? - Place the word 'EXPLAIN' at the beginning of the query, for example: - - EXPLAIN SELECT * FROM table1 WHERE age = 23; - + See the explain manual page. + 3.15) How do I create a serial field? Postgres does not allow the user to specifiy a user column as type @@ -683,6 +653,7 @@ BYTEA bytea variable-length array of bytes The default configuration allows only connections from tcp/ip host localhost. You need to add a host entry to the file pgsql/data/pg_hba. + See the hba_conf manual page. 3.18) How do I find out what indexes or operations are defined in the database? @@ -769,11 +740,20 @@ BYTEA bytea variable-length array of bytes We do not support ALTER TABLE DROP COLUMN, but do this: - SELECT ... # select all columns but the one you want to remove + SELECT ... -- select all columns but the one you want to remove INTO TABLE new_table FROM old_table; DROP TABLE old_table; ALTER TABLE new_table RENAME TO old_table; + + 3.23) How do SELECT only the first few rows of a query? + + See the fetch manual page. + + This only prevents all row results from being transfered to the + client. The entire query must be evaluated, even if you only want just + first few rows. Consider a query that has and ORDER BY. There is no + way to return any rows until the entire query is evaluated and sorted. _________________________________________________________________ Section 4: Extending PostgreSQL @@ -819,4 +799,4 @@ Section 5: Bugs You can also fill out the "bug-template" file and send it to: * bugs@postgreSQL.org - This is the address of the developers mailing list. + This is the address of the developers mailing list. |