接前面，繼續分析 chooseportalstrategy：
/*先展開第一段的判斷：if (list_length(stmts) == 1)* chooseportalstrategy
* select portal execution strategy given the intended statement list.
* * the list elements can be querys, plannedstmts, or utility statements.
* that's more general than portals need, but plancache.c uses this too.
* * see the comments in portal.h. */
portalstrategy
chooseportalstrategy(list *stmts)
if (query->commandtype == cmd_utility &&query->utilitystmt !=null)}}
else
if(isa(stmt, plannedstmt))}}
else
}/** portal_one_returning has to allow auxiliary queries added by rewrite.
* choose portal_one_returning if there is exactly one cansettag query and
* it has a returning list.
*/nsettag = 0
;
foreach
(lc, stmts)
}else
if(isa(stmt, plannedstmt))
}/*otherwise, utility command, assumed not cansettag */}
if (nsettag == 1
)
return
portal_one_returning;
/*else, it's the general case...
*/return
portal_multi_query;
}
其實是：
static inline int這裡我作乙個查詢驗證一下，list_length(
const list *l)
select * from tst01 where id in (select sid from tst02) or id in (select sid from tst03);
list_length(stmts) == 1 的條件滿足。
再看：
#define lfirst(lc) ((lc)->data.ptr_value)#define linitial(l) lfirst(list_head(l))
static inline listcell *list_head(所以呢，這句 ：node *stmt = (node *) lfirst(lc); 就是拿到了 計畫樹的頭，並且轉換為 node 指標。const list *l)
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