Обсуждение: inquiry

hello,

I have read the source code of postgres.c. Two strang things I can't understand.
Souce code of Postgres.c:
..
Foreach(parsetree_list的元素parsetree){ //In what situation here will be many parsetrees？
…
(List *)querytree_list = pg_analyze_and_rewrite(parsetree);foreach(querytree_list中的每个querytree){ //In what situation
herewill be many querytrees？ 

Who can tell me the reason?
Thank you very much

Jinqiang Han

Jinqiang Han wrote:
> hello,
>
> I have read the source code of postgres.c. Two strang things I can't understand.
> Souce code of Postgres.c:
> ..
> Foreach(parsetree_list��Ԫ��parsetree){ //In what situation here will be many parsetrees��
> ��

You can send multiple queries in a single string, "SELECT;SELECT".

> (List *)querytree_list = pg_analyze_and_rewrite(parsetree);
>     foreach(querytree_list�е�ÿ��querytree){ //In what situation here will be many querytrees��

A RULE may have additional queries to fire.

>
> Who can tell me the reason?
> Thank you very much
>
> Jinqiang Han
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 5: Have you checked our extensive FAQ?
>
> http://www.postgresql.org/docs/faqs/FAQ.html
>

--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@candle.pha.pa.us               |  (610)
359-1001+  If your life is a hard drive,     |  13 Roberts Road +  Christ can be your backup.        |  Newtown Square,
Pennsylvania19073 

hi,Bruce Momjian
I think you are wrong. multiple query in a string, such as ""SELECT;SELECT" will invoke pg_execute_query_string twice,
Itwon't generate two parsetree. 

======= 2003-03-26 10:20:00 您在来信中写道：=======

>Jinqiang Han wrote:
>> hello,
>>
>> I have read the source code of postgres.c. Two strang things I can't understand.
>> Souce code of Postgres.c:
>> ..
>> Foreach(parsetree_list的元素parsetree){ //In what situation here will be many parsetrees？
>> …
>
>You can send multiple queries in a single string, "SELECT;SELECT".
>
>> (List *)querytree_list = pg_analyze_and_rewrite(parsetree);
>>     foreach(querytree_list中的每个querytree){ //In what situation here will be many querytrees？
>
>A RULE may have additional queries to fire.
>
>>
>> Who can tell me the reason?
>> Thank you very much
>>
>> Jinqiang Han
>>
>>
>> ---------------------------(end of broadcast)---------------------------
>> TIP 5: Have you checked our extensive FAQ?
>>
>> http://www.postgresql.org/docs/faqs/FAQ.html
>>
>
>--
>  Bruce Momjian                        |  http://candle.pha.pa.us
>  pgman@candle.pha.pa.us               |  (610) 359-1001
>  +  If your life is a hard drive,     |  13 Roberts Road
>  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073
>
>.

= = = = = = = = = = = = = = = = = = = =

"Jinqiang Han" <postgresql@db.pku.edu.cn> writes:
> hi,Bruce Momjian
>     I think you are wrong. multiple query in a string, such as ""SELECT;SELECT" will invoke pg_execute_query_string
twice,It won't generate two parsetree.
 

Try it in something other than psql.  psql splits such a string into
multiple submissions to the backend --- but other interfaces don't.
        regards, tom lane