PostgreSQL代码分析,查询优化部分,pull_ands()和pull_ors()
PostgreSQL代码分析,查询优化部分。
这里把规范谓词表达式的部分就整理完了,阅读的顺序例如以下:
一、PostgreSQL代码分析,查询优化部分,canonicalize_qual
二、PostgreSQL代码分析,查询优化部分,pull_ands()和pull_ors()
三、PostgreSQL代码分析,查询优化部分,process_duplicate_ors
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pull_ands()和pull_ors()的代码比較便于理解,就是把树状结构的AND操作拉平,下图是pull_ands的样例,pull_ors逻辑同样:
/* * 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)); else out_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)); else out_list = lappend(out_list, subexpr); } return out_list; }
张大明确的blog:http://blog.csdn.net/shujiezhang