diff --git a/doc/FAQ b/doc/FAQ index 163178fa38..c188796c0e 100644 --- a/doc/FAQ +++ b/doc/FAQ @@ -1,7 +1,7 @@ Frequently Asked Questions (FAQ) for PostgreSQL - Last updated: Tue Apr 22 14:02:41 EDT 2003 + Last updated: Mon May 26 15:25:04 EDT 2003 Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us) @@ -60,7 +60,8 @@ 4.1) What is the difference between binary cursors and normal cursors? 4.2) How do I SELECT only the first few rows of a query? 4.3) How do I get a list of tables or other things I can see in psql? - 4.4) How do you remove a column from a table? + 4.4) How do you remove a column from a table, or change it's data + type? 4.5) What is the maximum size for a row, a table, and a database? 4.6) How much database disk space is required to store data from a typical text file? @@ -644,10 +645,10 @@ the -E option so it will print out the queries it uses to execute the commands you give. - 4.4) How do you remove a column from a table? + 4.4) How do you remove a column from a table, or change its data type? - This functionality was added in release 7.3 with ALTER TABLE DROP - COLUMN. In earlier versions, you can do this: + DROP COLUMN functionality was added in release 7.3 with ALTER TABLE + DROP COLUMN. In earlier versions, you can do this: BEGIN; LOCK TABLE old_table; SELECT ... -- select all columns but the one you want to remove @@ -657,6 +658,16 @@ ALTER TABLE new_table RENAME TO old_table; COMMIT; + To change the data type of a column, do this: + BEGIN; + ALTER TABLE tab ADD COLUMN new_col new_data_type; + UPDATE tab SET new_col = CAST(old_col AS new_data_type); + ALTER TABLE DROP COLUMN old_col; + COMMIT; + + You might then want to do VACUUM FULL tab to reclaim the disk space + used by the expired rows. + 4.5) What is the maximum size for a row, a table, and a database? These are the limits: diff --git a/doc/src/FAQ/FAQ.html b/doc/src/FAQ/FAQ.html index 33ba50b259..c63696aa58 100644 --- a/doc/src/FAQ/FAQ.html +++ b/doc/src/FAQ/FAQ.html @@ -10,7 +10,7 @@ alink="#0000ff">
Last updated: Tue Apr 22 14:02:41 EDT 2003
+Last updated: Mon May 26 15:25:04 EDT 2003
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
@@ -87,7 +87,7 @@
4.3) How do I get a list of tables or other
things I can see in psql?
4.4) How do you remove a column from a
- table?
+ table, or change it's data type?
4.5) What is the maximum size for a row, a
table, and a database?
4.6) How much database disk space is required
@@ -822,9 +822,9 @@
execute the commands you give.
This functionality was added in release 7.3 with +
DROP COLUMN functionality was added in release 7.3 with ALTER TABLE DROP COLUMN. In earlier versions, you can do this:
@@ -838,6 +838,17 @@ COMMIT;+
To change the data type of a column, do this:
++ BEGIN; + ALTER TABLE tab ADD COLUMN new_col new_data_type; + UPDATE tab SET new_col = CAST(old_col AS new_data_type); + ALTER TABLE DROP COLUMN old_col; + COMMIT; ++
You might then want to do VACUUM FULL tab to reclaim the + disk space used by the expired rows.
+