本節簡單介紹了PostgreSQL隱式類型轉換中使用哪些操作符(pg_operator)的實現函數func_match_argtypes.
一、數據結構
FuncCandidateList
該結構體存儲檢索得到的所有可能選中的函數或操作符鏈表.
/* * This structure holds a list of possible functions or operators * found by namespace lookup. Each function/operator is identified * by OID and by argument types; the list must be pruned by type * resolution rules that are embodied in the parser, not here. * See FuncnameGetCandidates's comments for more info. * 該結構體存儲檢索得到的所有可能選中的函數或操作符鏈表. * 每一個函數/操作符通過OID和參數類型唯一確定, * 通過集成到分析器中的type resolution rules來確定裁剪該鏈表(但不是在這裏實現) * 詳細可參考FuncnameGetCandidates函數. */typedef struct _FuncCandidateList{ struct _FuncCandidateList *next; //用於namespace檢索內部使用 int pathpos; /* for internal use of namespace lookup */ //OID Oid oid; /* the function or operator's OID */ //參數個數 int nargs; /* number of arg types returned */ //variadic array的參數個數 int nvargs; /* number of args to become variadic array */ //默認參數個數 int ndargs; /* number of defaulted args */ //參數位置索引 int *argnumbers; /* args' positional indexes, if named call */ //參數類型 Oid args[FLEXIBLE_ARRAY_MEMBER]; /* arg types */} *FuncCandidateList;二、源碼解讀
func_match_argtypes
給定候選函數列表(正確的函數名稱/參數個數匹配)和輸入數據類型OIDs數組,生成實際可匹配輸入數據類型(完全匹配或可轉換)的候選函數鏈表,然後符合條件的候選函數個數.
/* func_match_argtypes() * * Given a list of candidate functions (having the right name and number * of arguments) and an array of input datatype OIDs, produce a shortlist of * those candidates that actually accept the input datatypes (either exactly * or by coercion), and return the number of such candidates. * 給定候選函數列表(正確的函數名稱/參數個數匹配)和輸入數據類型OIDs數組, * 生成實際可匹配輸入數據類型(完全匹配或可轉換)的候選函數鏈表,然後符合條件的候選函數個數 * * Note that can_coerce_type will assume that UNKNOWN inputs are coercible to * anything, so candidates will not be eliminated on that basis. * can_coerce_type函數假定UNKNOWN輸入可轉換爲任意類型. * * NB: okay to modify input list structure, as long as we find at least * one match. If no match at all, the list must remain unmodified. * 注意:如果只是找到一個匹配的候選函數,修改輸入鏈表結構是OK的.如無匹配,則鏈表保持不變. */intfunc_match_argtypes(int nargs, Oid *input_typeids, FuncCandidateList raw_candidates, FuncCandidateList *candidates) /* return value */{ FuncCandidateList current_candidate;//當前候選 FuncCandidateList next_candidate;//下一候選 int ncandidates = 0; *candidates = NULL; for (current_candidate = raw_candidates; current_candidate != NULL; current_candidate = next_candidate)//遍歷候選函數 { next_candidate = current_candidate->next; if (can_coerce_type(nargs, input_typeids, current_candidate->args, COERCION_IMPLICIT))//可匹配輸入數據類型(完全匹配或可轉換) { current_candidate->next = *candidates; *candidates = current_candidate; ncandidates++; } } return ncandidates;} /* func_match_argtypes() */在pg_operator中,輸入參數類型與operator的參數類型匹配或可轉換,可進入候選函數鏈表.
三、跟蹤分析
測試腳本
create cast(integer as text) with inout as implicit;select id||'X' from t_cast;
跟蹤分析
(gdb) cContinuing.Breakpoint 2, oper_select_candidate (nargs=2, input_typeids=0x7ffeb9cca190, candidates=0x13db8a0, operOid=0x7ffeb9cca22c) at parse_oper.c:330330 ncandidates = func_match_argtypes(nargs, input_typeids,(gdb) p *candidates$1 = {next = 0x13db870, pathpos = 0, oid = 3284, nargs = 2, nvargs = 0, ndargs = 0, argnumbers = 0x0, args = 0x13db8c8}(gdb) p *candidates->next$2 = {next = 0x13db840, pathpos = 0, oid = 3681, nargs = 2, nvargs = 0, ndargs = 0, argnumbers = 0x0, args = 0x13db898}(gdb) p *candidates->next->next$3 = {next = 0x13db810, pathpos = 0, oid = 3633, nargs = 2, nvargs = 0, ndargs = 0, argnumbers = 0x0, args = 0x13db868}(gdb) p *candidates->next->next->next$4 = {next = 0x13db7e0, pathpos = 0, oid = 2780, nargs = 2, nvargs = 0, ndargs = 0, argnumbers = 0x0, args = 0x13db838}(gdb) p *candidates->next->next->next->next$5 = {next = 0x13db7b0, pathpos = 0, oid = 374, nargs = 2, nvargs = 0, ndargs = 0, argnumbers = 0x0, args = 0x13db808}(gdb) p *candidates->next->next->next->next->next$6 = {next = 0x13db780, pathpos = 0, oid = 349, nargs = 2, nvargs = 0, ndargs = 0, argnumbers = 0x0, args = 0x13db7d8}(gdb) p *candidates->next->next->next->next->next->next$7 = {next = 0x13db750, pathpos = 0, oid = 375, nargs = 2, nvargs = 0, ndargs = 0, argnumbers = 0x0, args = 0x13db7a8}(gdb) p *candidates->next->next->next->next->next->next->next$8 = {next = 0x13db720, pathpos = 0, oid = 1797, nargs = 2, nvargs = 0, ndargs = 0, argnumbers = 0x0, args = 0x13db778}(gdb) p *candidates->next->next->next->next->next->next->next->next$9 = {next = 0x13db6f0, pathpos = 0, oid = 2779, nargs = 2, nvargs = 0, ndargs = 0, argnumbers = 0x0, args = 0x13db748}(gdb) p *candidates->next->next->next->next->next->next->next->next->next$10 = {next = 0x13db6c0, pathpos = 0, oid = 654, nargs = 2, nvargs = 0, ndargs = 0, argnumbers = 0x0, args = 0x13db718}(gdb) p *candidates->next->next->next->next->next->next->next->next->next->next$11 = {next = 0x0, pathpos = 0, oid = 2018, nargs = 2, nvargs = 0, ndargs = 0, argnumbers = 0x0, args = 0x13db6e8}(gdb) p *candidates->next->next->next->next->next->next->next->next->next->next->nextCannot access memory at address 0x0(gdb) n334 if (ncandidates == 0)(gdb) 339 if (ncandidates == 1)(gdb) 349 candidates = func_select_candidate(nargs, input_typeids, candidates);(gdb) p ncandidates$12 = 2(gdb) p *candidates$13 = {next = 0x13db810, pathpos = 0, oid = 374, nargs = 2, nvargs = 0, ndargs = 0, argnumbers = 0x0, args = 0x13db808}(gdb) p *candidates->next$14 = {next = 0x0, pathpos = 0, oid = 2780, nargs = 2, nvargs = 0, ndargs = 0, argnumbers = 0x0, args = 0x13db838}(gdb) p *candidates->next->nextCannot access memory at address 0x0(gdb)DONE! 鄭州×××醫院×××：http://myyk.familydoctor.com.cn/yiyuanzaixian/zztjyy//