E.52. Postgres95版本 0.03

E.52.1. 修改列表

不兼容的变化：
 * BETA-0.3 IS INCOMPATIBLE WITH DATABASES CREATED WITH PREVIOUS VERSIONS
   (due to system catalog changes and indexing structure changes).
 * double-quote (") is deprecated as a quoting character for string literals;
   you need to convert them to single quotes ('). 
 * name of aggregates (eg. int4sum) are renamed in accordance with the
   SQL standard (eg. sum).
 * CHANGE ACL syntax is replaced by GRANT/REVOKE syntax.
 * float literals (eg. 3.14) are now of type float4 (instead of float8 in
   previous releases); you might have to do typecasting if you depend on it
   being of type float8.  If you neglect to do the typecasting and you assign
   a float literal to a field of type float8, you may get incorrect values
   stored!
 * LIBPQ has been totally revamped so that frontend applications
   can connect to multiple backends
 * the usesysid field in pg_user has been changed from int2 to int4 to
   allow wider range of Unix user ids.
 * the netbsd/freebsd/bsd o/s ports have been consolidated into a
   single BSD44_derived port.  (thanks to Alistair Crooks)

SQL 标准兼容(下列详细的改变令 postgres95 与 SQL-92 标准更加兼容)∶
 * the following SQL types are now built-in: smallint, int(eger), float, real,
   char(N), varchar(N), date and time.

   The following are aliases to existing postgres types:
		smallint -> int2
		integer, int -> int4
		float, real  -> float4
   char(N) and varchar(N) are implemented as truncated text types. In
   addition, char(N) does blank-padding. 
 * single-quote (') is used for quoting string literals; '' (in addition to
   \') is supported as means of inserting a single quote in a string
 * SQL standard aggregate names (MAX, MIN, AVG, SUM, COUNT) are used
   (Also, aggregates can now be overloaded, i.e. you can define your
   own MAX aggregate to take in a user-defined type.)
 * CHANGE ACL removed. GRANT/REVOKE syntax added.  
   - Privileges can be given to a group using the "GROUP" keyword.
	For example:
		GRANT SELECT ON foobar TO GROUP my_group;
	The keyword 'PUBLIC' is also supported to mean all users.	

	Privileges can only be granted or revoked to one user or group
	at a time.  

	"WITH GRANT OPTION" is not supported.  Only class owners can change
	access control
   - The default access control is to to grant users readonly access.
     You must explicitly grant insert/update access to users.  To change
     this, modify the line in 
		src/backend/utils/acl.h 
     that defines ACL_WORLD_DEFAULT 

修补：
 * the bug where aggregates of empty tables were not run has been fixed. Now,
   aggregates run on empty tables will return the initial conditions of the
   aggregates. Thus, COUNT of an empty	table will now properly return 0.
   MAX/MIN of an empty table will return a tuple of value NULL. 
 * allow the use of \; inside the monitor
 * the LISTEN/NOTIFY asynchronous notification mechanism now work
 * NOTIFY in rule action bodies now work
 * hash indexes work, and access methods in general should perform better.
   creation of large btree indexes should be much faster.  (thanks to Paul
   Aoki)

其它修改和增强：
 * addition of an EXPLAIN statement used for explaining the query execution
   plan (eg. "EXPLAIN SELECT * FROM EMP" prints out the execution plan for
   the query).
 * WARN and NOTICE messages no longer have timestamps on them. To turn on
   timestamps of error messages, uncomment the line in
   src/backend/utils/elog.h:
	/* define ELOG_TIMESTAMPS */ 
 * On an access control violation, the message
	"Either no such class or insufficient privilege"
   will be given.  This is the same message that is returned when
   a class is not found.  This dissuades non-privileged users from
   guessing the existence of privileged classes.
 * some additional system catalog changes have been made that are not
   visible to the user.

libpgtcl 修改：
 * The -oid option has been added to the "pg_result" tcl command.
   pg_result -oid returns oid of the last tuple inserted.   If the
   last command was not an INSERT, then pg_result -oid returns "".
 * the large object interface is available as pg_lo* tcl commands:
   pg_lo_open, pg_lo_close, pg_lo_creat, etc.

可移植性增强和新的移植：
 * flex/lex problems have been cleared up.  Now, you should be able to use
   flex instead of lex on any platforms.  We no longer make assumptions of
   what lexer you use based on the platform you use. 
 * The Linux-ELF port is now supported.  Various configuration have been 
   tested:  The following configuration is known to work:
	kernel 1.2.10, gcc 2.6.3, libc 4.7.2, flex 2.5.2, bison 1.24
   with everything in ELF format,

新应用：
 * ipcclean added to the distribution
   ipcclean usually does not need to be run, but if your backend crashes
   and leaves shared memory segments hanging around, ipcclean will
   clean them up for you.

新文档：
 * the user manual has been revised and libpq documentation added.