相关： 《Postgresql源码（56）可扩展类型分析ExpandedObject/ExpandedRecord》
本文探索raise notice 'sqlstate: %', sqlstate;时，%的值是怎么拿到的。
0 总结
- plpgsql中通过SPI调用server语法解析时不需要加select，例如
src="sqlstate"就可以直接跑，不需要`src=“select sqlstate”。gram.y中可以匹配按a_expr解析。 - 取值流程：
- 入口：paramvalue = exec_eval_expr
- `[1]` 生成执行计划exec_prepare_plan
- 在pg_analyze_and_rewrite_params开始时会调钩子配置ParseState：用plpgsql_parser_setup给ParseState的四个变量赋予三个钩子函数，一个变量expr。
- 在优化器里面会用前面配置的回调函数plpgsql_post_column_ref识别sqlstate列的类型。
- `[2]` 执行执行计划exec_eval_simple_expr
- 进入表达式执行分支：ExecEvalExpr
- 表达式为PARAM回调类型，走EEOP_PARAM_CALLBACK分支回调PL的plpgsql_param_eval_var_ro拿值，值拼接成扩展类型返回：[《Postgresql源码（56）可扩展类型分析ExpandedObject/ExpandedRecord》](https://blog.csdn.net/jackgo73/article/details/125372466)exec_eval_expr
[1] exec_prepare_plan
SPI_prepare_extended(expr->query, &options);
_SPI_begin_call
_SPI_prepare_plan
raw_parser
pg_analyze_and_rewrite_params
[2] exec_eval_simple_expr
ExecInitExprWithParams
ExecEvalExpr
ExecInterpExprStillValid
ExecInterpExpr
EEO_CASE(EEOP_PARAM_CALLBACK)
plpgsql_param_eval_var_ro
var = (PLpgSQL_var *) estate->datums[dno];
*op->resvalue = MakeExpandedObjectReadOnly(var->value, var->isnull, -1);1 案例
本文探索raise notice 'sqlstate: %', sqlstate;时，%的值是怎么拿到的。
do $g$
BEGIN
RAISE division_by_zero;
EXCEPTION
WHEN division_by_zero THEN
raise notice 'sqlstate: %', sqlstate;
raise notice 'sqlerrm: %', sqlerrm;
END;
$g$;
-- NOTICE: sqlstate: 22012
-- NOTICE: sqlerrm: division_by_zero2 执行raise notice时如何给%赋值
当前PLpgSQL_stmt_raise的值：
代码语言：javascript复制PLpgSQL_stmt_raise
{cmd_type = PLPGSQL_STMT_RAISE,
lineno = 6, stmtid = 2, elog_level = 18,
condname = 0x0,
message = 0x104d338 "sqlstate: %",
params = 0x104d860,
-> [List]
-> [PLpgSQL_expr]
--> {query = 0x104d838 "sqlstate", parseMode = RAW_PARSE_PLPGSQL_EXPR,
plan = 0x0, paramnos = 0x0, func = 0x0, ns = 0x104d1f8,
expr_simple_expr = 0x0, expr_simple_type = 0, expr_simple_typmod = 0,
expr_simple_mutable = false, target_param = -1, expr_rw_param = 0x0,
expr_simple_plansource = 0x0, expr_simple_plan = 0x0, expr_simple_plan_lxid = 0,
expr_simple_state = 0x0, expr_simple_in_use = false, expr_simple_lxid = 0}
options = 0x0}执行流程
代码语言：javascript复制exec_stmt_raise
...
...
if (stmt->message) // "sqlstate: %"
{
StringInfoData ds;
ListCell *current_param;
char *cp;
MemoryContext oldcontext;
oldcontext = MemoryContextSwitchTo(stmt_mcontext); // 进入"PLpgSQL per-statement data"
initStringInfo(&ds);
MemoryContextSwitchTo(oldcontext);
current_param = list_head(stmt->params);
for (cp = stmt->message; *cp; cp )
{
if (cp[0] == '%') // "sqlstate: %" 匹配到 "%”
{
Oid paramtypeid;
int32 paramtypmod;
Datum paramvalue;
bool paramisnull;
char *extval;
...
paramvalue = exec_eval_expr(estate, // 进入 exec_eval_expr 下面展开分析
(PLpgSQL_expr *) lfirst(current_param),
¶misnull, // 获取 参数为空？
¶mtypeid, // 获取 参数类型？
¶mtypmod); // 获取 返回类型？
// 拿到执行结果 Datum 指向 "22012"
if (paramisnull)
extval = "<NULL>";
else
extval = convert_value_to_string(estate, // 结果转换为字符串 "22012"
paramvalue,
paramtypeid);
appendStringInfoString(&ds, extval); // 在"sqlstate: " 后面拼上 "22012"
current_param = lnext(stmt->params, current_param);
exec_eval_cleanup(estate);
}
else
appendStringInfoChar(&ds, cp[0]);
}
/* should have been checked at compile time */
if (current_param != NULL)
elog(ERROR, "unexpected RAISE parameter list length");
err_message = ds.data;
}
...
...重要函数：exec_eval_expr
入参：
代码语言：javascript复制expr -> [PLpgSQL_expr]
--> {query = 0x104d838 "sqlstate", parseMode = RAW_PARSE_PLPGSQL_EXPR,
plan = 0x0, paramnos = 0x0, func = 0x0, ns = 0x104d1f8,
expr_simple_expr = 0x0, expr_simple_type = 0, expr_simple_typmod = 0,
expr_simple_mutable = false, target_param = -1, expr_rw_param = 0x0,
expr_simple_plansource = 0x0, expr_simple_plan = 0x0, expr_simple_plan_lxid = 0,
expr_simple_state = 0x0, expr_simple_in_use = false, expr_simple_lxid = 0}流程：
代码语言：javascript复制exec_eval_expr
exec_prepare_plan(estate, expr, CURSOR_OPT_PARALLEL_OK)
// 【第一步】拼SPIPrepareOptions options
expr->func = estate->func; // 存执行信息的总结构
options.parserSetup
= (ParserSetupHook) plpgsql_parser_setup; // 给动态参数的获取装钩子
// 给执行器提供函数：plpgsql_pre_column_ref
// 给执行器提供函数：plpgsql_post_column_ref
// 给执行器提供函数：plpgsql_param_ref
// 给执行器提供变量：PLpgSQL_expr *expr
options.parserSetupArg = (void *) expr; // 挂上上面expr结构
options.parseMode = expr->parseMode;
options.cursorOptions = cursorOptions;
// SPIPrepareOptions {
// parserSetup = 0x7fc1755fa264 <plpgsql_parser_setup>,
// parserSetupArg = 0x104d7a0, --> parserSetup和parserSetupArg 是一对，Arg是给上面函数的参数
// parseMode = RAW_PARSE_PLPGSQL_EXPR,
// cursorOptions = 2048}
// 【第二步】执行query = "sqlstate"
SPI_prepare_extended(expr->query, &options);重要函数：SPI_prepare_extended
1 SPI_prepare_extended第一步：_SPI_begin_call 准备上下文、 拼接Plan
代码语言：javascript复制SPI_prepare_extended
_SPI_begin_call // 切换上下文 "SPI Proc" --> "SPI Exec"
... // 拼接_SPI_plan
// _SPI_plan {
// magic = 569278163,
// saved = false,
// oneshot = false,
// plancache_list = 0x0,
// plancxt = 0x0,
// parse_mode = RAW_PARSE_PLPGSQL_EXPR,
// cursor_options = 2048,
// nargs = 0,
// argtypes = 0x0,
// parserSetup = 0x7fc1755fa264 <plpgsql_parser_setup>, --> 给执行器的钩子，钩子需要下面的expr
// parserSetupArg = 0x104d7a0} --> PLpgSQL_expr2 SPI_prepare_extended第二步：开始执行_SPI_prepare_plan
代码语言：javascript复制 _SPI_prepare_plan(src, &plan) // src = "sqlstate"- 语法解析
raw_parser(src, plan->parse_mode) // plan->parse_mode = RAW_PARSE_PLPGSQL_EXPR
(1) base_yylex->[736]->[MODE_PLPGSQL_EXPR]
(2) base_yylex->[258]->[IDENT]
(3) base_yylex->[0]
(4) ColId: | unreserved_keyword { $$ = pstrdup($1); }
(5) columnref: ColId { $$ = makeColumnRef($1, NIL, @1, yyscanner); }
{type = T_ColumnRef, fields = 0x1047238, location = 0}
fields -> [List] -> {type = T_String, val = {str = "sqlstate"}}
(6) c_expr: | AexprConst { $$ = $1; }
(7) a_expr: | a_expr TYPECAST Typename { $$ = makeTypeCast($1, $3, @2); }
(8) target_el: | a_expr { $$ = makeNode(ResTarget); $$->val = (Node *)$1; $$->location = @1; }
(9) target_list: | target_list ',' target_el { $$ = lappend($1, $3); }
(10)opt_target_list: | { $$ = NULL; }
...
raw_parsetree_list -> [List] ->
{type = T_RawStmt, stmt = 0x1047368, stmt_location = 0, stmt_len = 0}
stmt -> [SelectStmt] -> {type = T_SelectStmt, ..., targetList = 0x10472e8}
targetList -> [List]
-> [ResTarget]
-> {type = T_ResTarget, val = 0x10471d8}
val -> [ColumnRef] -> {type = T_ColumnRef, fields = 0x1047238}
fields -> [List] -> {type = T_String, val = {str = "sqlstate"}}- 优化器
通过钩子函数，成功构造Param {xpr = {type = T_Param}, paramkind = PARAM_EXTERN, paramid = 2, paramtype = 25, paramtypmod = -1, paramcollid = 100, location = 0}
pg_analyze_and_rewrite_params(parsetree, src, plan->parserSetup, plan->parserSetupArg,...)
// plpgsql_parser_setup给ParseState的四个变量赋予三个钩子函数，一个变量
(*parserSetup) (pstate, parserSetupArg)
transformTopLevelStmt
transformOptionalSelectInto
transformStmt
transformSelectStmt
transformTargetList
transformTargetEntry
transformExpr
transformExprRecurse
transformColumnRef(ParseState *pstate, ColumnRef *cref)
// ColumnRef {type = T_ColumnRef, fields = 0x1047238, location = 0}
// parserSetup的钩子在pg_analyze_and_rewrite_params第三、四个参数传入
// 如果配了钩子，直接返回钩子函数构造的node：pstate->p_pre_columnref_hook
// 进入PLPGSQL：
plpgsql_pre_column_ref // 钩子进入plpgsql_pre_column_ref返回NULL
plpgsql_post_column_ref // 钩子进入plpgsql_post_column_ref
resolve_column_ref
// 按A | A.B | A.B.C 解析出变量名字到name1、name2、name3
plpgsql_ns_lookup(...,name1,name2,name3,...) // 查询变量名字
// nse->itemno = 1 cref->location = 0
// 构造Param {xpr = {type = T_Param}, paramkind = PARAM_EXTERN,
// paramid = 2, paramtype = 25,
// paramtypmod = -1, paramcollid = 100, location = 0}
// paramid = 2 == dnp 1 记录参数位置
return make_datum_param(expr, nse->itemno, cref->location)- 继续执行拿到SPIPlanPtr
result = _SPI_make_plan_non_temp(&plan)
_SPI_end_call(true)
return result
[ SPIPlanPtr ]
{ magic = 569278163, saved = false, oneshot = false,
plancache_list = 0xf7b5e8,
plancxt = 0xf7b470,
parse_mode = RAW_PARSE_PLPGSQL_EXPR,
cursor_options = 2048,
nargs = 0, argtypes = 0x0,
parserSetup = 0x7fc1755fa264 <plpgsql_parser_setup>,
parserSetupArg = 0x10459b0}3 SPI_prepare_extended第三步：开始执行exec_eval_simple_expr
代码语言：javascript复制exec_eval_simple_expr
ExecInitExprWithParams
ExecEvalExpr
ExecInterpExprStillValid
ExecInterpExpr
EEO_CASE(EEOP_PARAM_CALLBACK)
plpgsql_param_eval_var_ro
var = (PLpgSQL_var *) estate->datums[dno];
*op->resvalue = MakeExpandedObjectReadOnly(var->value,
var->isnull,
-1);
