這篇文章主要講解了“PostgreSQL隱式類型轉(zhuǎn)換中使用哪些操作符實(shí)現(xiàn)函數(shù)”，文中的講解內(nèi)容簡(jiǎn)單清晰，易于學(xué)習(xí)與理解，下面請(qǐng)大家跟著小編的思路慢慢深入，一起來研究和學(xué)習(xí)“PostgreSQL隱式類型轉(zhuǎn)換中使用哪些操作符實(shí)現(xiàn)函數(shù)”吧！
創(chuàng)新互聯(lián)堅(jiān)持“要么做到，要么別承諾”的工作理念，服務(wù)領(lǐng)域包括：成都網(wǎng)站設(shè)計(jì)、網(wǎng)站制作、企業(yè)官網(wǎng)、英文網(wǎng)站、手機(jī)端網(wǎng)站、網(wǎng)站推廣等服務(wù)，滿足客戶于互聯(lián)網(wǎng)時(shí)代的昌邑網(wǎng)站設(shè)計(jì)、移動(dòng)媒體設(shè)計(jì)的需求，幫助企業(yè)找到有效的互聯(lián)網(wǎng)解決方案。努力成為您成熟可靠的網(wǎng)絡(luò)建設(shè)合作伙伴！
FuncCandidateList
該結(jié)構(gòu)體存儲(chǔ)檢索得到的所有可能選中的函數(shù)或操作符鏈表.
重慶分公司
重慶分公司
/*
* 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(jié)構(gòu)體存儲(chǔ)檢索得到的所有可能選中的函數(shù)或操作符鏈表.
* 每一個(gè)函數(shù)/操作符通過OID和參數(shù)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(但不是在這里實(shí)現(xiàn))
* 詳細(xì)可參考FuncnameGetCandidates函數(shù).
*/
typedef struct _FuncCandidateList
{
struct _FuncCandidateList *next;
//用于namespace檢索內(nèi)部使用
int pathpos; /* for internal use of namespace lookup */
//OID
Oid oid; /* the function or operator's OID */
//參數(shù)個(gè)數(shù)
int nargs; /* number of arg types returned */
//variadic array的參數(shù)個(gè)數(shù)
int nvargs; /* number of args to become variadic array */
//默認(rèn)參數(shù)個(gè)數(shù)
int ndargs; /* number of defaulted args */
//參數(shù)位置索引
int *argnumbers; /* args' positional indexes, if named call */
//參數(shù)類型
Oid args[FLEXIBLE_ARRAY_MEMBER]; /* arg types */
} *FuncCandidateList;func_match_argtypes
給定候選函數(shù)列表(正確的函數(shù)名稱/參數(shù)個(gè)數(shù)匹配)和輸入數(shù)據(jù)類型OIDs數(shù)組,生成實(shí)際可匹配輸入數(shù)據(jù)類型(完全匹配或可轉(zhuǎn)換)的候選函數(shù)鏈表,然后符合條件的候選函數(shù)個(gè)數(shù).
/* 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(shù)列表(正確的函數(shù)名稱/參數(shù)個(gè)數(shù)匹配)和輸入數(shù)據(jù)類型OIDs數(shù)組,
* 生成實(shí)際可匹配輸入數(shù)據(jù)類型(完全匹配或可轉(zhuǎn)換)的候選函數(shù)鏈表,然后符合條件的候選函數(shù)個(gè)數(shù)
*
* 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(shù)假定UNKNOWN輸入可轉(zhuǎn)換為任意類型.
*
* 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(gè)匹配的候選函數(shù),修改輸入鏈表結(jié)構(gòu)是OK的.如無匹配,則鏈表保持不變.
*/
int
func_match_argtypes(int nargs,
Oid *input_typeids,
FuncCandidateList raw_candidates,
FuncCandidateList *candidates) /* return value */
{
FuncCandidateList current_candidate;//當(dāng)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(shù)
{
next_candidate = current_candidate->next;
if (can_coerce_type(nargs, input_typeids, current_candidate->args,
COERCION_IMPLICIT))//可匹配輸入數(shù)據(jù)類型(完全匹配或可轉(zhuǎn)換)
{
current_candidate->next = *candidates;
*candidates = current_candidate;
ncandidates++;
}
}
return ncandidates;
} /* func_match_argtypes() */在pg_operator中,輸入?yún)?shù)類型與operator的參數(shù)類型匹配或可轉(zhuǎn)換,可進(jìn)入候選函數(shù)鏈表.
測(cè)試腳本
create cast(integer as text) with inout as implicit; select id||'X' from t_cast;
跟蹤分析
(gdb) c
Continuing.
Breakpoint 2, oper_select_candidate (nargs=2, input_typeids=0x7ffeb9cca190, candidates=0x13db8a0, operOid=0x7ffeb9cca22c)
at parse_oper.c:330
330 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->next
Cannot access memory at address 0x0
(gdb) n
334 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->next
Cannot access memory at address 0x0
(gdb)感謝各位的閱讀，以上就是“PostgreSQL隱式類型轉(zhuǎn)換中使用哪些操作符實(shí)現(xiàn)函數(shù)”的內(nèi)容了，經(jīng)過本文的學(xué)習(xí)后，相信大家對(duì)PostgreSQL隱式類型轉(zhuǎn)換中使用哪些操作符實(shí)現(xiàn)函數(shù)這一問題有了更深刻的體會(huì)，具體使用情況還需要大家實(shí)踐驗(yàn)證。這里是創(chuàng)新互聯(lián)，小編將為大家推送更多相關(guān)知識(shí)點(diǎn)的文章，歡迎關(guān)注！
