这里分析一下函数中应用绑定变量的问题，但实际应用场景中，不推荐这么使用。
prepare divplan2(int,int) as select div($1,$2);
execute divplan2(4,2);
语法解析
分别分析prepare语句以及execute语句。
gram.y中定义
/********************************************************************* QUERY:* PREPARE <plan_name> [(args, ...)] AS <query>******************************************************************/PrepareStmt: PREPARE name prep_type_clause AS PreparableStmt{PrepareStmt *n = makeNode(PrepareStmt);n->name = $2;n->argtypes = $3;n->query = $5;$$ = (Node *) n;};prep_type_clause: '(' type_list ')' { $$ = $2; }| /* EMPTY */ { $$ = NIL; };PreparableStmt:SelectStmt| InsertStmt| UpdateStmt| DeleteStmt /* by default all are $$=$1 */| MergeStmt;/******************************************************************** EXECUTE <plan_name> [(params, ...)]******************************************************************/
ExecuteStmt: EXECUTE name execute_param_clause{ExecuteStmt *n = makeNode(ExecuteStmt);n->name = $2;n->params = $3;$$ = (Node *) n;}execute_param_clause: '(' expr_list ')' { $$ = $2; }| /* EMPTY */ { $$ = NIL; };
主流程
prepare，execute语句代码主流程如下，
main
--> PostmasterMain--> ServerLoop--> BackendStartup--> BackendRun--> PostgresMain--> exec_simple_query
exec_simple_query
--> pg_parse_query
--> pg_analyze_and_rewrite
--> pg_plan_queries
--> PortalStart
--> PortalRun--> PortalRunUtiliey--> standard_ProcessUtility--> PrepareQuery // prepare语句--> ExecuteQuery // execute语句--> DeallocateQuery
prepare语句
prepare divplan2(int,int) as select div($1,$2);
Prepare语句主流程如下：
PrepareQuery
--> CreateCachedPlan // 创建CachedPlanSource
--> parse_analyze_varparams // 语义分析--> parse_variable_parameters--> transformTopLevelStmt--> transformStmt--> transformSelectStmt--> transformTargetList--> transformTargetEntry--> transformExpr--> transformFuncCall // 解析函数调用--> transformParamRef // 解析绑定变量参数，构造Param节点,作为函数参数--> variable_paramref_hook --> ParseFuncOrColumn // 构造FuncExpr， 获取函数oid,返回值类型oid--> func_get_detail--> FuncnameGetCandidates // 通过函数名获取后续函数列表--> func_match_argtypes--> func_select_candidate--> make_fn_arguments--> coerce_type--> variable_coerce_param_hook--> check_variable_parameters
--> QueryRewrite // 查询重写
--> CompleteCachedPlan // 创建plan cache entry
--> StorePreparedStatement // 存到哈希表中--> InitQueryHashTable /* Initialize the hash table, if necessary */--> hash_create --> hash_search /* Add entry to hash table */--> SaveCachedPlan // save a cached plan permanently--> ReleaseGenericPlan--> dlist_push_tail
execute语句
execute divplan2(4,2);
Execute主流程如下：
ExecuteQuery
--> FetchPreparedStatement // 哈希表中查找是否有已缓存的执行计划--> hash_search
--> CreateExecutorState
--> EvaluateParams // 获取绑定变量参数，返回ParamListInfo--> ExecPrepareExprList--> ExecPrepareExpr--> expression_planner--> eval_const_expressions--> ExecInitExpr--> makeParamList 获取到参数值4,2
--> CreateNewPortal--> CreatePortal
--> GetCachedPlan--> RevalidateCachedQuery--> choose_custom_plan // choose whether to use custom or generic plan--> if (!customplan) // 走generic plan--> if (CheckCachedPlan)// 直接获取已有的有效generic planelse--> BuildCachedPlan--> pg_plan_queries--> pg_plan_query--> planner--> standard_planner--> subquery_planner--> preprocess_expression // 复合常量化简，直接调用函数--> eval_const_expressions--> simplify_function --> evaluate_function--> evaluate_expr--> cached_plan_cost--> if (customplan) // 走custom plan--> BuildCachedPlan--> pg_plan_queries--> pg_plan_query--> planner--> standard_planner--> subquery_planner--> preprocess_qual_conditions--> eval_const_expressions--> create_plan--> PortalDefineQuery
--> PortalStart--> ExecutorStart--> InitPlan
--> PortalRun--> ExecutorRun--> standard_ExecutorRun--> ExecutePlan--> PortalDrop--> ExecutorEnd--> standard_ExecutorEnd--> ExecEndPlan--> PortalReleaseCachedPlan /* drop cached plan reference, if any */
)
