# 正文

`PostgreSQL`的`psql`客户端提供`\x`元命令，可以按列（扩展）显示查询结果，例如：

```sql
postgres=# select * from aot;
 slot_time | slot_count |  event  | event_count | event_rate 
-----------+------------+---------+-------------+------------
 21:00:00  |          3 | Event 1 |           2 |      33.33
 21:01:00  |          4 | Event 1 |           4 |      33.34
(2 rows)

# 切换到扩展显示模式
seaboxsql=# \x
Expanded display is on.
seaboxsql=# select * from aot;
-[ RECORD 1 ]---------
slot_time   | 21:00:00
slot_count  | 3
event       | Event 1
event_count | 2
event_rate  | 33.33
-[ RECORD 2 ]---------
slot_time   | 21:01:00
slot_count  | 4
event       | Event 1
event_count | 4
event_rate  | 33.34
```

同样地，`MySQL`客户端也提供`\G`类似元命令。

然而，`Oracle`的`sqlplus`没有提供此种显示模式。我们可以通过间接方式实现。

定义一个过程：

```sql
create or replace procedure print_table( p_query in varchar2 )
AUTHID CURRENT_USER
is
	l_theCursor integer default dbms_sql.open_cursor;
	l_columnValue varchar2(4000);
	l_status integer;
	l_descTbl dbms_sql.desc_tab;
	l_colCnt number;
begin
	execute immediate
	'alter session set nls_date_format=''yyyy-mm-dd hh24:mi:ss'' ';

	dbms_sql.parse( l_theCursor, p_query, dbms_sql.native );
	dbms_sql.describe_columns( l_theCursor, l_colCnt, l_descTbl );

	for i in 1 .. l_colCnt loop
		dbms_sql.define_column(l_theCursor, i, l_columnValue, 4000);
	end loop;

	l_status := dbms_sql.execute(l_theCursor);

	while ( dbms_sql.fetch_rows(l_theCursor) > 0 ) 
	loop
		for i in 1 .. l_colCnt loop
			dbms_sql.column_value
			( l_theCursor, i, l_columnValue );
			dbms_output.put_line
			( rpad( l_descTbl(i).col_name, 30 )
			|| ': ' || 
			l_columnValue );
		end loop;
		dbms_output.put_line( '-----------------' );
	end loop;
	execute immediate 'alter session set nls_date_format=''dd-MON-rr'' ';
	
	exception
		when others then
		execute immediate 'alter session set nls_date_format=''dd-MON-rr'' ';
		raise;
end;
/
```

使用过程：

```sql
SQL> set serveroutput on;
SQL> exec print_table('select * from v$database');
DBID                          : 2867884909
NAME                          : ORCLCDB
CREATED                       : 2022-02-16 17:12:13
RESETLOGS_CHANGE#             : 1920977
RESETLOGS_TIME                : 2022-02-16 17:12:16
PRIOR_RESETLOGS_CHANGE#       : 1
……
-----------------

PL/SQL procedure successfully completed.
```

# 参考

1. [print_table 实现 sqlplus 类似 mysql \G 及 psql \x 的功能](https://blog.csdn.net/ctypyb2002/article/details/107490215)
2. [re: prior posting on index - Ask TOM](https://asktom.oracle.com/ords/f?p=100:11:0::::P11_QUESTION_ID:1035431863958)