PostgreSQL程式碼分析，查詢最佳化部分，pull_ands()和pull_ors()

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PostgreSQL程式碼分析，查詢最佳化部分。

這裡把正式指令動詞運算式的部分就整理完了，閱讀的順序如下：

一、PostgreSQL程式碼分析，查詢最佳化部分，canonicalize_qual

二、PostgreSQL程式碼分析，查詢最佳化部分，pull_ands()和pull_ors()

三、PostgreSQL程式碼分析，查詢最佳化部分，process_duplicate_ors

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pull_ands()和pull_ors()的代碼比較便於理解，就是把樹狀結構的AND操作拉平，是pull_ands的例子，pull_ors邏輯相同：

/* * pull_ands *  Recursively flatten nested AND clauses into a single and-clause list. * * Input is the arglist of an AND clause. * Returns the rebuilt arglist (note original list structure is not touched). */static List *pull_ands(List *andlist){List   *out_list = NIL;ListCell   *arg;foreach(arg, andlist){Node   *subexpr = (Node *) lfirst(arg);/* * Note: we can destructively concat the subexpression's arglist * because we know the recursive invocation of pull_ands will have * built a new arglist not shared with any other expr. Otherwise we'd * need a list_copy here. */if (and_clause(subexpr))out_list = list_concat(out_list,   pull_ands(((BoolExpr *) subexpr)->args));elseout_list = lappend(out_list, subexpr);}return out_list;}/* * pull_ors *  Recursively flatten nested OR clauses into a single or-clause list. * * Input is the arglist of an OR clause. * Returns the rebuilt arglist (note original list structure is not touched). */static List *pull_ors(List *orlist){List   *out_list = NIL;ListCell   *arg;foreach(arg, orlist){Node   *subexpr = (Node *) lfirst(arg);/* * Note: we can destructively concat the subexpression's arglist * because we know the recursive invocation of pull_ors will have * built a new arglist not shared with any other expr. Otherwise we'd * need a list_copy here. */if (or_clause(subexpr))out_list = list_concat(out_list,   pull_ors(((BoolExpr *) subexpr)->args));elseout_list = lappend(out_list, subexpr);}return out_list;}

張大明白的blog：http://blog.csdn.net/shujiezhang

PostgreSQL程式碼分析，查詢最佳化部分，pull_ands()和pull_ors()