Postgresql源码（41）plpgsql函数编译执行流程分析

相关
《Postgresql源码（41）plpgsql函数编译执行流程分析》
《Postgresql源码（46）plpgsql中的变量类型及对应关系》
《Postgresql源码（49）plpgsql函数编译执行流程分析总结》
《Postgresql源码（53）plpgsql语法解析关键流程、函数分析》
《Postgresql源码（112）plpgsql执行sql时变量何时替换为值》

这篇写的细节比较多有点乱，大体流程和总结可以看第三、四篇 《Postgresql源码（49）plpgsql函数编译执行流程分析总结》和《Postgresql源码（53）plpgsql语法解析关键流程、函数分析》

全文总结

编译

1、编译过程主要是pl_gram.y做语法匹配的过程plpgsql_yyparse，整体匹配后的结果会作为PLpgSQL_stmt_block结构记录在plpgsql_parse_result中。

2、PLpgSQL_stmt_block结构分别记录两个核心List：body和exception，两个链表会记录所有执行节点（普通语句串到body后，when…then后的串到exception后）

3、编译过程会记录符号表：单链表ns_top记录所有使用的符号。

4、编译过程会记录变量值：数组plpgsql_Datums（数组个数plpgsql_nDatums），记录所有变量。

执行

1、执行过程整体框架在exec_stmt_block函数中

2、如果有异常处理：PG_TRY --> exec_stmts(estate, block->body) --> PG_CATCH --> exec_stmts(estate, exception->action)

3、如果没有异常处理：exec_stmts(estate, block->body)

分析实例

drop table tf1;
create table tf1(c1 int, c2 int,  c3 varchar(32), c4 varchar(32), c5 int);
insert into tf1 values(1,1000, 'China','Dalian', 23000);
insert into tf1 values(2,4000, 'Janpan', 'Tokio', 45000);
insert into tf1 values(3,1500, 'China', 'Xian', 25000);
insert into tf1 values(4,300, 'China', 'Changsha', 24000);
insert into tf1 values(5,400,'USA','New York', 35000);
insert into tf1 values(6,5000, 'USA', 'Bostom', 15000);


======================================
PG
======================================
CREATE  OR REPLACE FUNCTION tfun1(p3 text, x3 int[]) RETURNS text AS $$
DECLARE
  row1 tf1%ROWTYPE;
  row2 tf1%ROWTYPE;
	txt1 text;
	x1 int[];
	n1 int := 1;
BEGIN

	RAISE NOTICE 'start division_by_zero n1';
	n1 = n1 / 0;
  EXCEPTION
    WHEN division_by_zero THEN
        RAISE NOTICE 'caught division_by_zero do nothing';
  
	RAISE NOTICE 'start print x1';
  FOREACH x1 SLICE 1 IN ARRAY $2
  LOOP
    RAISE NOTICE 'row = %', x1;
  END LOOP;	

  RAISE NOTICE 'start connecting c4';
	txt1 = p3 || ':';
    FOR row1 IN SELECT * FROM tf1 WHERE c3 = p3
	LOOP
		row2.c4 = row1.c4;
		txt1 = txt1 || row2.c4 ||'+';
	END LOOP;
	return txt1;
END;
$$ LANGUAGE plpgsql;

select tfun1('China', ARRAY[[1,2,3],[4,5,6],[7,8,9],[10,11,12]]);

执行结果

postgres=# select tfun1('China', ARRAY[[1,2,3],[4,5,6],[7,8,9],[10,11,12]]);
NOTICE:  start division_by_zero n1
NOTICE:  caught division_by_zero do nothing
NOTICE:  start print x1
NOTICE:  row = {1,2,3}
NOTICE:  row = {4,5,6}
NOTICE:  row = {7,8,9}
NOTICE:  row = {10,11,12}
NOTICE:  start connecting c4
            tfun1            
-----------------------------
 China:Dalian+Xian+Changsha+

1 编译

CreateFunction

ProcessUtilitySlow
  CreateFunction
    QualifiedNameGetCreationNamespace					：【1】解析namespace名称
    pg_namespace_aclcheck								：【2】权限检查
    compute_attributes_sql_style						：【3】解析函数体外部as、LANGUAGE等参数构造成的DefElem结构
    （参数是哪来的？gram.y中匹配出来的）
    =====================================
        gram.y：
    =====================================
				createfunc_opt_item:
							AS func_as
								{
									$$ = makeDefElem("as", (Node *)$2, @1);
								}
							| LANGUAGE NonReservedWord_or_Sconst
								{
									$$ = makeDefElem("language", (Node *)makeString($2), @1);
								}
							| TRANSFORM transform_type_list
								{
									$$ = makeDefElem("transform", (Node *)$2, @1);
								}
							| WINDOW
								{
									$$ = makeDefElem("window", (Node *)makeInteger(true), @1);
								}
							| common_func_opt_item
								{
									$$ = $1;
								}
						;

		  DefElem *
			makeDefElem(char *name, Node *arg, int location)
			{
				DefElem    *res = makeNode(DefElem);
			
				res->defnamespace = NULL;
				res->defname = name;
				res->arg = arg;
				res->defaction = DEFELEM_UNSPEC;
				res->location = location;
			
				return res;
			}
      =====================================
      SearchSysCache1(LANGNAME, PointerGetDatum(language))				：【3】在系统表pg_language中匹配语言、权限检查
      interpret_function_parameter_list									：【4】构造入参列表，入参参数检查
      compute_return_type												：【5】构造返回参数列表，检查返回值参数
        ProcedureCreate

ProcedureCreate

ProcedureCreate
  ...
  heap_modify_tuple														：构造一行插入pg_proc
  ...
  /* Verify function body */
  OidFunctionCall1(languageValidator, ObjectIdGetDatum(retval))			：走语言提供的验证器开始验证函数内容
    FunctionCall1Coll
      FunctionCallInvoke
        plpgsql_validator												：只传一个PROC的OID进来，在去系统表里拿这一行
          // SPI start													：打开SPI可以在函数内执行SQL，编译可能不需要
          plpgsql_compile(fake_fcinfo, true)							：开始编译函数体
          // SPI end

plpgsql_compile

第一阶段参数解析

【1】初始化PLpgSQL_nsitem *ns_top

【2】ns_top装入函数名

【3】初始化128个PLpgSQL_datum

【4】初始化 出参数、入参数

【5】用plpgsql_build_datatype的结果构造variable，计入全局datum list数组

plpgsql_compile
  function = plpgsql_HashTableLookup(&hashkey)					：已经编译过的函数信息记录进入hash表，构造key可以快速查询
  do_compile																												：开始编译
    prosrcdatum = SysCacheGetAttr(PROCOID...)					：从系统表拿proc
    proc_source = TextDatumGetCString(prosrcdatum)				：拿到源码
    
    memset(function, 0, sizeof(PLpgSQL_function));				：清空PLpgSQL_function重新构造
    
    plpgsql_ns_init();											：【1】初始化PLpgSQL_nsitem *ns_top
    /*===============================================
    // Item in the compilers namespace tree
    typedef struct PLpgSQL_nsitem
    {
    	PLpgSQL_nsitem_type itemtype;
    
    	
    	// For labels, itemno is a value of enum PLpgSQL_label_type. For other
    	// itemtypes, itemno is the associated PLpgSQL_datum's dno.
    	
    	int			itemno;
    	struct PLpgSQL_nsitem *prev;
    	char		name[FLEXIBLE_ARRAY_MEMBER];	// nul-terminated string
    } PLpgSQL_nsitem;
    ===============================================*/
    
    plpgsql_ns_push(NameStr(procStruct->proname)...)	：【2】ns_top装入函数名{itemtype = PLPGSQL_NSTYPE_LABEL, itemno = 0, prev = 0x0, name = 0x2ef8118 "tfun1"}
    plpgsql_start_datums()								：【3】初始化128个PLpgSQL_datum
      													：plpgsql_nDatums：当前位置
      													：plpgsql_Datums：数组
    /*=============================================
    // 
    // Generic datum array item										： 注意！ PLpgSQL_datum是下面这四个类型的小头
    // 																： PLpgSQL_var  PLpgSQL_rec
    // PLpgSQL_datum is the common supertype for PLpgSQL_var, 		： PLpgSQL_row  PLpgSQL_recfield
    // PLpgSQL_row,													： 
    // PLpgSQL_rec, and PLpgSQL_recfield.							： PLpgSQL_variable是上面四个类型的大头
    // 
    typedef struct PLpgSQL_datum
    {
    	PLpgSQL_datum_type dtype;
    	int			dno;
    } PLpgSQL_datum;
    ===============================================*/
    switch (function->fn_is_trigger)
      PLPGSQL_NOT_TRIGGER												：触发器fn走单独的分支，这里是普通函数
    	  in_arg_varnos = (int *) palloc(numargs * sizeof(int))			：【4】初始化 出参数、入参数
        out_arg_variables = (PLpgSQL_variable **) palloc(numargs * sizeof(PLpgSQL_variable *))
        for (i = 0; i < numargs; i++)
          argdtype = plpgsql_build_datatype
          argvariable = plpgsql_build_variable							：【5】用plpgsql_build_datatype的结果构造variable，计入全局datum list数组
         																：循环结束，参数里面的变量添加完毕
          																：ns_top和val状态是什么？
    /*===============================================
    --------> ns_top <--------											：现在两个结构的状态
    $129 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 1, prev = 0x2ef8378, name = 0x2ef83c0 "x3"}
    $130 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 1, prev = 0x2ef8210, name = 0x2ef8388 "$2"}
    $131 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 0, prev = 0x2ef81d8, name = 0x2ef8220 "p3"}
    $132 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 0, prev = 0x2ef8108, name = 0x2ef81e8 "$1"}
    $133 = {itemtype = PLPGSQL_NSTYPE_LABEL, itemno = 0, prev = 0x0, name = 0x2ef8118 "tfun1"}
   
    --------> plpgsql_nDatums <--------
    --------> plpgsql_Datums  <--------
    $136 = {dtype = PLPGSQL_DTYPE_VAR, dno = 0}
    
    (gdb) p *((PLpgSQL_var*)plpgsql_Datums[0])
    $139 = {
      dtype = PLPGSQL_DTYPE_VAR, dno = 0, refname = 0x2ef81b8 "p3", 
      lineno = 0, isconst = false, notnull = false, default_val = 0x0, 
      datatype = 0x2ef8140, cursor_explicit_expr = 0x0, cursor_explicit_argrow = 0, 
      cursor_options = 0, value = 0, isnull = true, freeval = false, promise = PLPGSQL_PROMISE_NONE}
    $137 = {dtype = PLPGSQL_DTYPE_VAR, dno = 1}

    (gdb) p *((PLpgSQL_var*)plpgsql_Datums[1])
    $140 = {
      dtype = PLPGSQL_DTYPE_VAR, dno = 1, refname = 0x2ef8358 "x3", 
      lineno = 0, isconst = false, notnull = false, default_val = 0x0, 
      datatype = 0x2ef8248, cursor_explicit_expr = 0x0, cursor_explicit_argrow = 0, 
      cursor_options = 0, value = 0, isnull = true, freeval = false, promise = PLPGSQL_PROMISE_NONE}
    ===============================================*/
    var = plpgsql_build_variable("found"...)	：构造found变量
    											：全局ns_top和var各新增一条
    /*===============================================
    $143 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 2, prev = 0x2ef83b0, name = 0x2ef8528 "found"}
    
    (gdb) p *((PLpgSQL_var*)plpgsql_Datums[2])
    $149 = {
      dtype = PLPGSQL_DTYPE_VAR, dno = 2, refname = 0x2ef84f8 "found", 
      lineno = 0, isconst = false, notnull = false, default_val = 0x0, 
      datatype = 0x2ef83e8, cursor_explicit_expr = 0x0, cursor_explicit_argrow = 0, 
      cursor_options = 0, value = 0, isnull = true, freeval = false, promise = PLPGSQL_PROMISE_NONE}
    ===============================================*/
    
    parse_rc = plpgsql_yyparse()				：开始解析 // b plpgsql_ns_push

第二阶段函数体解析——声明部分

（这里可以用gdb断这个pl_gram.y的函数了）

【1】开始pl_gram.y解析，这里可以用gdb断这个文件的函数了

【2】解析参数声明部分

【】解析其他部分

【3】所有的结果在gram.y中一级一级的汇总到$$中，最后在父节点传给全局变量plpgsql_parse_result，所有节点都用List挂在body上。

do_compile
  ...
  parse_rc = plpgsql_yyparse();						：【1】开始pl_gram.y解析，这里可以用gdb断这个文件的函数了
  
  function->action = plpgsql_parse_result;			：【3】所有的结果在gram.y中一级一级的汇总到$$中，最后在父节点传给全局变量plpgsql_parse_result
  
  
      (pl_gram.y语法树截取) 
    decl_datatype	:								：【2】解析参数声明部分
					{
						$$ = read_datatype(yychar);	：read_datatype构造数据记录到plpgsql_Datums、ns_top
						yyclearin;
					}
				;
    /*===============================================
    DECLARE
      row1 tf1%ROWTYPE;
      row2 tf1%ROWTYPE;
	    txt1 text;
	    x1 int[];
	    n1 int := 1;
	    
	  看下新增的plpgsql_Datums、ns_top
	  p *ns_top
    $25 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 7, prev = 0x2f2dac0, name = 0x2f2e490 "n1"}	  
    $27 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 6, prev = 0x2f366e8, name = 0x2f2dad0 "x1"}
    $28 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 5, prev = 0x2f36340, name = 0x2f366f8 "txt1"}
    $29 = {itemtype = PLPGSQL_NSTYPE_REC, itemno = 4, prev = 0x2f36108, name = 0x2f36350 "row2"}
    $30 = {itemtype = PLPGSQL_NSTYPE_REC, itemno = 3, prev = 0x2f35ed0, name = 0x2f36118 "row1"}
    $31 = {itemtype = PLPGSQL_NSTYPE_LABEL, itemno = 0, prev = 0x2f35e98, name = 0x2f35ee0 ""}
    $32 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 2, prev = 0x2f35d30, name = 0x2f35ea8 "found"}
    $33 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 1, prev = 0x2f35cf8, name = 0x2f35d40 "x3"}
    $34 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 1, prev = 0x2f35b90, name = 0x2f35d08 "$2"}
    $35 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 0, prev = 0x2f35b58, name = 0x2f35ba0 "p3"}
    $36 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 0, prev = 0x2f35a88, name = 0x2f35b68 "$1"}
    $37 = {itemtype = PLPGSQL_NSTYPE_LABEL, itemno = 0, prev = 0x0, name = 0x2f35a98 "tfun1"}
	  
	  p *((PLpgSQL_var*)plpgsql_Datums[3])
    $19 = {
      dtype = PLPGSQL_DTYPE_REC, dno = 3, refname = 0x2f360e8 "row1", 
      lineno = 3, isconst = false, notnull = false, default_val = 0x0,
      datatype = 0x2f36018, cursor_explicit_expr = 0xffffffff00004004, 
      cursor_explicit_argrow = 0, cursor_options = 0, value = 9187201950435737470, 
      isnull = 8, freeval = false, promise = PLPGSQL_PROMISE_NONE}
      
    p *((PLpgSQL_var*)plpgsql_Datums[4])
    $20 = {
      dtype = PLPGSQL_DTYPE_REC, dno = 4, refname = 0x2f36320 "row2", 
      lineno = 4, isconst = false, notnull = false, default_val = 0x0,
      datatype = 0x2f36250, cursor_explicit_expr = 0xffffffff00004004, 
      cursor_explicit_argrow = 0, cursor_options = 0, value = 9187201950435737470, 
      isnull = 8, freeval = false, promise = PLPGSQL_PROMISE_NONE}
    
    p *((PLpgSQL_var*)plpgsql_Datums[5])
    $21 = {
      dtype = PLPGSQL_DTYPE_VAR, dno = 5, refname = 0x2f2d268 "txt1", 
      lineno = 5, isconst = false, notnull = false, default_val = 0x0,
      datatype = 0x2f2d158, cursor_explicit_expr = 0x0, 
      cursor_explicit_argrow = 0, cursor_options = 0, value = 0, isnull = true, 
      freeval = false, promise = PLPGSQL_PROMISE_NONE}
    
    p *((PLpgSQL_var*)plpgsql_Datums[6])
    $22 = {
      dtype = PLPGSQL_DTYPE_VAR, dno = 6, refname = 0x2f2daa0 "x1", 
      lineno = 6, isconst = false, notnull = false, default_val = 0x0, 
      datatype = 0x2f2d990, cursor_explicit_expr = 0x0, 
      cursor_explicit_argrow = 0, cursor_options = 0, value = 0, isnull = true, 
      freeval = false, promise = PLPGSQL_PROMISE_NONE}
      
    p *((PLpgSQL_var*)plpgsql_Datums[7])
    $23 = {
      dtype = PLPGSQL_DTYPE_VAR, dno = 7, refname = 0x2f2e460 "n1", 
      lineno = 7, isconst = false, notnull = false, default_val = 0x2f2e310, 
      datatype = 0x2f2e298, cursor_explicit_expr = 0x0, 
      cursor_explicit_argrow = 0, cursor_options = 0, value = 0,
      isnull = true, freeval = false, promise = PLPGSQL_PROMISE_NONE}
    ===============================================*/
    
  

第三阶段函数体解析——第一句：RAISE NOTICE 'start division_by_zero n1';

总结：解析树拼PLpgSQL_stmt_raise然后返回！

stmt_raise		: K_RAISE
					{
						PLpgSQL_stmt_raise		*new;
						int	tok;

						new = palloc(sizeof(PLpgSQL_stmt_raise));

						new->cmd_type	= PLPGSQL_STMT_RAISE;
						new->lineno		= plpgsql_location_to_lineno(@1);
						new->stmtid		= ++plpgsql_curr_compile->nstatements;
						new->elog_level = ERROR;	/* default */
						new->condname	= NULL;
						new->message	= NULL;
						new->params		= NIL;
						new->options	= NIL;

						tok = yylex();
            ...
						if (tok != ';')
						{
							...
              ...
              // RAISE NOTICE 'start division_by_zero n1'
              //       |
              //   解析NOTICE
							else if (tok_is_keyword(tok, &yylval,
													K_NOTICE, "notice"))
							{
								new->elog_level = NOTICE;
                // 解析下一个符号
								tok = yylex();
							}
							...
              ...
              ...
              // RAISE NOTICE 'start division_by_zero n1';
              //              |
		      //		 解析名字
							if (tok == SCONST)start division_by_zero n1
							{
								// start division_by_zero n1
								new->message = yylval.str;
								tok = yylex();
                // RAISE NOTICE 'start division_by_zero n1';
                //   									   |
                // 										解析分号
								if (tok != ',' && tok != ';' && tok != K_USING)
									yyerror("syntax error");

								...

						check_raise_parameters(new);

						$$ = (PLpgSQL_stmt *)new;
					}
				;

第三阶段函数体解析——第二句：n1 = n1 / 0;

总结：解析树拼PLpgSQL_stmt_assign然后返回！

stmt_assign		: T_DATUM
					{
						PLpgSQL_stmt_assign *new;
						RawParseMode pmode;

						/* see how many names identify the datum */
						switch ($1.ident ? 1 : list_length($1.idents))
						{
							case 1:
								pmode = RAW_PARSE_PLPGSQL_ASSIGN1;
								break;
							case 2:
								pmode = RAW_PARSE_PLPGSQL_ASSIGN2;
								break;
							case 3:
								pmode = RAW_PARSE_PLPGSQL_ASSIGN3;
								break;
							default:
								elog(ERROR, "unexpected number of names");
								pmode = 0; /* keep compiler quiet */
						}

						check_assignable($1.datum, @1);
						new = palloc0(sizeof(PLpgSQL_stmt_assign));
						new->cmd_type = PLPGSQL_STMT_ASSIGN;
						new->lineno   = plpgsql_location_to_lineno(@1);
						new->stmtid = ++plpgsql_curr_compile->nstatements;
						new->varno = $1.datum->dno;
						/* Push back the head name to include it in the stmt */
						plpgsql_push_back_token(T_DATUM);
						new->expr = read_sql_construct(';', 0, 0, ";",
													   pmode,
													   false, true, true,
													   NULL, NULL);

						$$ = (PLpgSQL_stmt *)new;
					}
				;

返回值：
(gdb) p *new
$58 = {cmd_type = PLPGSQL_STMT_ASSIGN, lineno = 11, stmtid = 2, varno = 7, expr = 0x2f2e710}
(gdb) p *new->expr
$59 = {
  query = 0x2f2e7a8 "n1 = n1 / 0", 
  parseMode = RAW_PARSE_PLPGSQL_ASSIGN1, 
  plan = 0x0, paramnos = 0x0, func = 0x0, ns = 0x2f2e480, 
  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}

第三阶段函数体解析——第三句： EXCEPTION WHEN division_by_zero THEN ...

第一步：遇到EXCEPTION不管后面是什么，先新建连个变量：

b plpgsql_yyparse
b tok_is_keyword
b plpgsql_build_variable
b read_datatype
/*=========================================================
SQL语句：

目前只关心——————>>>  EXCEPTION
    			WHEN division_by_zero THEN
        		RAISE NOTICE 'caught division_by_zero do nothing';
=========================================================*/

语法解析：
exception_sect	:
					{ $$ = NULL; }
				| K_EXCEPTION
					{
						int			lineno = plpgsql_location_to_lineno(@1);
						PLpgSQL_exception_block *new = palloc(sizeof(PLpgSQL_exception_block));
						PLpgSQL_variable *var;

						var = plpgsql_build_variable("sqlstate", lineno,
													 plpgsql_build_datatype(TEXTOID,
																			-1,
																			plpgsql_curr_compile->fn_input_collation,
																			NULL),
													 true);
						var->isconst = true;
						new->sqlstate_varno = var->dno;

						var = plpgsql_build_variable("sqlerrm", lineno,
													 plpgsql_build_datatype(TEXTOID,
																			-1,
																			plpgsql_curr_compile->fn_input_collation,
																			NULL),
													 true);
						var->isconst = true;
						new->sqlerrm_varno = var->dno;

						$<exception_block>$ = new;
/*=========================================================
  (gdb)  p *((PLpgSQL_var*)plpgsql_Datums[8])
  $69 = {
    dtype = PLPGSQL_DTYPE_VAR, dno = 8, refname = 0x2f2c920 "sqlstate", 
    lineno = 12, isconst = true, notnull = false, 
    default_val = 0x0, datatype = 0x2f2c810, cursor_explicit_expr = 0x0, c
    ursor_explicit_argrow = 0, cursor_options = 0, value = 0, 
    isnull = true, freeval = false, promise = PLPGSQL_PROMISE_NONE}
  
  (gdb)  p *((PLpgSQL_var*)plpgsql_Datums[9])
  $70 = {
    dtype = PLPGSQL_DTYPE_VAR, dno = 9, refname = 0x2f2ca58 "sqlerrm", 
    lineno = 12, isconst = true, notnull = false,
    default_val = 0x0, datatype = 0x2f2c948, cursor_explicit_expr = 0x0, 
    cursor_explicit_argrow = 0, cursor_options = 0, value = 0, 
    isnull = true, freeval = false, promise = PLPGSQL_PROMISE_NONE}
    
  (gdb) p *ns_top
  $71 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 9, prev = 0x2edaa90, name = 0x2f2ca88 "sqlerrm"}
  (gdb) p *ns_top->prev
  $72 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 8, prev = 0x2eda880, name = 0x2edaaa0 "sqlstate"}
  (gdb) p *ns_top->prev->prev
  $73 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 7, prev = 0x2ed9ec0, name = 0x2eda890 "n1"}
  =========================================================*/
					}
					proc_exceptions
					{
						PLpgSQL_exception_block *new = $<exception_block>2;
						new->exc_list = $3;

						$$ = new;
					}
				;

第二步：解析EXCEPTION后面部分

/*=========================================================
SQL语句：

					EXCEPTION
目前只关心——————>>>		WHEN division_by_zero THEN
目前只关心——————>>>		RAISE NOTICE 'caught division_by_zero do nothing';
=========================================================*/

proc_exceptions	: proc_exceptions proc_exception
						{
							$$ = lappend($1, $2);
						}
				| proc_exception
						{
							$$ = list_make1($1);
						}
				;

proc_exception	: K_WHEN proc_conditions K_THEN proc_sect
					{
						PLpgSQL_exception *new;

						new = palloc0(sizeof(PLpgSQL_exception));
						new->lineno = plpgsql_location_to_lineno(@1);
						new->conditions = $2;
						new->action = $4;

						$$ = new;
					}
				;

proc_conditions	: proc_conditions K_OR proc_condition
						{
							PLpgSQL_condition	*old;

							for (old = $1; old->next != NULL; old = old->next)
								/* skip */ ;
							old->next = $3;
							$$ = $1;
						}
				| proc_condition
						{
							$$ = $1;
						}
				;

proc_condition	: any_identifier
						{
							if (strcmp($1, "sqlstate") != 0)
							{
								$$ = plpgsql_parse_err_condition($1);						：走这里解析非sqlstate xxx格式的异常例如 division_by_zero	
							}																									：exception_label_map[i]里面找division_by_zero，匹配了就构造一个PLpgSQL_condition返回
							else			
							{
								PLpgSQL_condition *new;
								char   *sqlstatestr;

								/* next token should be a string literal */
								if (yylex() != SCONST)
									yyerror("syntax error");
								sqlstatestr = yylval.str;

								if (strlen(sqlstatestr) != 5)
									yyerror("invalid SQLSTATE code");
								if (strspn(sqlstatestr, "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ") != 5)
									yyerror("invalid SQLSTATE code");

								new = palloc(sizeof(PLpgSQL_condition));
								new->sqlerrstate =
									MAKE_SQLSTATE(sqlstatestr[0],
												  sqlstatestr[1],
												  sqlstatestr[2],
												  sqlstatestr[3],
												  sqlstatestr[4]);
								new->condname = sqlstatestr;
								new->next = NULL;

								$$ = new;
							}
						}
				;

第三阶段函数体解析——第四句： FOREACH x1 SLICE 1 IN ARRAY $2 ...

// SQL语句
FOREACH x1 SLICE 1 IN ARRAY $2
LOOP
  RAISE NOTICE 'row = %', x1;
END LOOP;	


stmt_foreach_a	: opt_loop_label K_FOREACH for_variable foreach_slice K_IN K_ARRAY expr_until_loop loop_body
					{
						PLpgSQL_stmt_foreach_a *new;

						new = palloc0(sizeof(PLpgSQL_stmt_foreach_a));
						new->cmd_type = PLPGSQL_STMT_FOREACH_A;
						new->lineno = plpgsql_location_to_lineno(@2);
						new->stmtid = ++plpgsql_curr_compile->nstatements;
						new->label = $1;
						new->slice = $4;
						new->expr = $7;
						new->body = $8.stmts;

						if ($3.row)
						{
							new->varno = $3.row->dno;
							check_assignable($3.row, @3);
						}
						else if ($3.scalar)
						{
							new->varno = $3.scalar->dno;
							check_assignable($3.scalar, @3);
						}
						else
						{
							ereport(ERROR,
									(errcode(ERRCODE_SYNTAX_ERROR),
									 errmsg("loop variable of FOREACH must be a known variable or list of variables"),
											 parser_errposition(@3)));
						}

						check_labels($1, $8.end_label, $8.end_label_location);
						plpgsql_ns_pop();

						$$ = (PLpgSQL_stmt *) new;
					}
				;
				
datums没变，目前ns_top状态：
	p *ns_top
	pop出去了-->$8 = {itemtype = PLPGSQL_NSTYPE_LABEL, itemno = 1, prev = 0x2f15458, name = 0x2f15718 ""}
	$9 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 9, prev = 0x2edb2b0, name = 0x2f15468 "sqlerrm"}
	$10 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 8, prev = 0x2edb0a0, name = 0x2edb2c0 "sqlstate"}
    $25 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 7, prev = 0x2f2dac0, name = 0x2f2e490 "n1"}	  
    $27 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 6, prev = 0x2f366e8, name = 0x2f2dad0 "x1"}
    $28 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 5, prev = 0x2f36340, name = 0x2f366f8 "txt1"}
    $29 = {itemtype = PLPGSQL_NSTYPE_REC, itemno = 4, prev = 0x2f36108, name = 0x2f36350 "row2"}
    $30 = {itemtype = PLPGSQL_NSTYPE_REC, itemno = 3, prev = 0x2f35ed0, name = 0x2f36118 "row1"}
    $31 = {itemtype = PLPGSQL_NSTYPE_LABEL, itemno = 0, prev = 0x2f35e98, name = 0x2f35ee0 ""}
    $32 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 2, prev = 0x2f35d30, name = 0x2f35ea8 "found"}
    $33 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 1, prev = 0x2f35cf8, name = 0x2f35d40 "x3"}
    $34 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 1, prev = 0x2f35b90, name = 0x2f35d08 "$2"}
    $35 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 0, prev = 0x2f35b58, name = 0x2f35ba0 "p3"}
    $36 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 0, prev = 0x2f35a88, name = 0x2f35b68 "$1"}
    $37 = {itemtype = PLPGSQL_NSTYPE_LABEL, itemno = 0, prev = 0x0, name = 0x2f35a98 "tfun1"}
	  

第三阶段函数体解析——第五句： txt1 = p3 || ':';

拼接一个PLpgSQL_stmt_assign结构

stmt_assign		: T_DATUM
					{
						PLpgSQL_stmt_assign *new;
						RawParseMode pmode;

						/* see how many names identify the datum */
						switch ($1.ident ? 1 : list_length($1.idents))
						{
							case 1:
								pmode = RAW_PARSE_PLPGSQL_ASSIGN1;
								break;
							case 2:
								pmode = RAW_PARSE_PLPGSQL_ASSIGN2;
								break;
							case 3:
								pmode = RAW_PARSE_PLPGSQL_ASSIGN3;
								break;
							default:
								elog(ERROR, "unexpected number of names");
								pmode = 0; /* keep compiler quiet */
						}

						check_assignable($1.datum, @1);
						new = palloc0(sizeof(PLpgSQL_stmt_assign));
						new->cmd_type = PLPGSQL_STMT_ASSIGN;
						new->lineno   = plpgsql_location_to_lineno(@1);
						new->stmtid = ++plpgsql_curr_compile->nstatements;
						new->varno = $1.datum->dno;
						/* Push back the head name to include it in the stmt */
						plpgsql_push_back_token(T_DATUM);
						new->expr = read_sql_construct(';', 0, 0, ";",
													   pmode,
													   false, true, true,
													   NULL, NULL);

						$$ = (PLpgSQL_stmt *)new;
					}
				;

返回PLpgSQL_stmt_assign

(gdb) p new
$15 = (PLpgSQL_stmt_assign *) 0x2f15c00
  
(gdb) p *new
$16 = {cmd_type = PLPGSQL_STMT_ASSIGN, lineno = 23, stmtid = 8, varno = 5, expr = 0x2f15c98}

(gdb) p *new->expr
$17 = {
  query = 0x2f15d30 "txt1 = p3 || ':'", 
  parseMode = RAW_PARSE_PLPGSQL_ASSIGN1, 
  plan = 0x0, paramnos = 0x0, func = 0x0, 
  ns = 0x2f15458, 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}

(gdb) p *new->expr->ns
$18 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 9, prev = 0x2edb2b0, name = 0x2f15468 "sqlerrm"}

第三阶段函数体解析——第六句： FOR...LOOP...END LOOP

for语法解析

/*
 * Processing the for_variable is tricky because we don't yet know if the
 * FOR is an integer FOR loop or a loop over query results.  In the former
 * case, the variable is just a name that we must instantiate as a loop
 * local variable, regardless of any other definition it might have.
 * Therefore, we always save the actual identifier into $$.name where it
 * can be used for that case.  We also save the outer-variable definition,
 * if any, because that's what we need for the loop-over-query case.  Note
 * that we must NOT apply check_assignable() or any other semantic check
 * until we know what's what.
 *
 * However, if we see a comma-separated list of names, we know that it
 * can't be an integer FOR loop and so it's OK to check the variables
 * immediately.  In particular, for T_WORD followed by comma, we should
 * complain that the name is not known rather than say it's a syntax error.
 * Note that the non-error result of this case sets *both* $$.scalar and
 * $$.row; see the for_control production.
 */
for_variable	: T_DATUM
					{
						$$.name = NameOfDatum(&($1));
						$$.lineno = plpgsql_location_to_lineno(@1);
						if ($1.datum->dtype == PLPGSQL_DTYPE_ROW ||
							$1.datum->dtype == PLPGSQL_DTYPE_REC)
						{
							$$.scalar = NULL;
							$$.row = $1.datum;
						}
						else
						{
							int			tok;

							$$.scalar = $1.datum;
							$$.row = NULL;
							/* check for comma-separated list */
							tok = yylex();
							plpgsql_push_back_token(tok);
							if (tok == ',')
								$$.row = (PLpgSQL_datum *)
									read_into_scalar_list($$.name,
														  $$.scalar,
														  @1);
						}
					}
				| T_WORD
					{
						int			tok;

						$$.name = $1.ident;
						$$.lineno = plpgsql_location_to_lineno(@1);
						$$.scalar = NULL;
						$$.row = NULL;
						/* check for comma-separated list */
						tok = yylex();
						plpgsql_push_back_token(tok);
						if (tok == ',')
							word_is_not_variable(&($1), @1);
					}
				| T_CWORD
					{
						/* just to give a better message than "syntax error" */
						cword_is_not_variable(&($1), @1);
					}
				;

编译结果分析（通过plpgsql_parse_result返回）

代码位置

do_compile
  ...
  ...
  /*
	 * Now parse the function's text
	 */
	parse_rc = plpgsql_yyparse();
	if (parse_rc != 0)
		elog(ERROR, "plpgsql parser returned %d", parse_rc);
	function->action = plpgsql_parse_result;

	plpgsql_scanner_finish();
	pfree(proc_source);

检查plpgsql_parse_result结构

猜猜为什么body只有两个stmt？？

(gdb) p *plpgsql_parse_result
$31 = {
  cmd_type = PLPGSQL_STMT_BLOCK, lineno = 8, stmtid = 13, label = 0x0, 
  body = 0x2edb1e0, n_initvars = 5, initvarnos = 0x2edb0d8, exceptions = 0x2f151c8}

(gdb) p *plpgsql_parse_result->initvarnos
$38 = 3

===========================
body
===========================
(gdb) p *plpgsql_parse_result->body
$34 = {type = T_List, length = 2, max_length = 5, elements = 0x2edb1f8, initial_elements = 0x2edb1f8}

(gdb) tr PLpgSQL_stmt plpgsql_parse_result->body->elements[0]
$59 = {cmd_type = PLPGSQL_STMT_RAISE, lineno = 10, stmtid = 1}

(gdb) tr PLpgSQL_stmt_raise plpgsql_parse_result->body->elements[0]
$61 = {cmd_type = PLPGSQL_STMT_RAISE, lineno = 10, stmtid = 1, elog_level = 18, condname = 0x0,
  message = 0x2edb1a8 "start division_by_zero n1", params = 0x0, options = 0x0}

(gdb) tr PLpgSQL_stmt plpgsql_parse_result->body->elements[1]
$60 = {cmd_type = PLPGSQL_STMT_ASSIGN, lineno = 11, stmtid = 2}

(gdb) p *((PLpgSQL_stmt_assign*)plpgsql_parse_result->body->elements[1])->expr
$67 = {query = 0x2f15178 "n1 = n1 / 0", parseMode = RAW_PARSE_PLPGSQL_ASSIGN1, plan = 0x0, paramnos = 0x0, func = 0x0, ns = 0x2edb0a0, 
  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}

(gdb) tr PLpgSQL_stmt_assign plpgsql_parse_result->body->elements[1]
$65 = {cmd_type = PLPGSQL_STMT_ASSIGN, lineno = 11, stmtid = 2, varno = 7, expr = 0x2f150e0}

===========================
exceptions
===========================
(gdb) p *plpgsql_parse_result->exceptions
$33 = {sqlstate_varno = 8, sqlerrm_varno = 9, exc_list = 0x2f16780}

因为按照上面的写法，后面执行的foreach等stmt都挂在exctption里面了！

检查ns_top

编译时用到的都删了，就剩下函数明确定义的符号 和 隐含符号$1 $2 found

    $32 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 2, prev = 0x2f35d30, name = 0x2f35ea8 "found"}
    $33 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 1, prev = 0x2f35cf8, name = 0x2f35d40 "x3"}
    $34 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 1, prev = 0x2f35b90, name = 0x2f35d08 "$2"}
    $35 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 0, prev = 0x2f35b58, name = 0x2f35ba0 "p3"}
    $36 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 0, prev = 0x2f35a88, name = 0x2f35b68 "$1"}
    $37 = {itemtype = PLPGSQL_NSTYPE_LABEL, itemno = 0, prev = 0x0, name = 0x2f35a98 "tfun1"}

检查datum

 
	p *((PLpgSQL_var*)plpgsql_Datums[0])
  $139 = {
    dtype = PLPGSQL_DTYPE_VAR, dno = 0, refname = 0x2ef81b8 "p3", 
    lineno = 0, isconst = false, notnull = false, default_val = 0x0, 
    datatype = 0x2ef8140, cursor_explicit_expr = 0x0, cursor_explicit_argrow = 0, 
    cursor_options = 0, value = 0, isnull = true, freeval = false, promise = PLPGSQL_PROMISE_NONE}
  $137 = {dtype = PLPGSQL_DTYPE_VAR, dno = 1}

  p *((PLpgSQL_var*)plpgsql_Datums[1])
  $140 = {
    dtype = PLPGSQL_DTYPE_VAR, dno = 1, refname = 0x2ef8358 "x3", 
    lineno = 0, isconst = false, notnull = false, default_val = 0x0, 
    datatype = 0x2ef8248, cursor_explicit_expr = 0x0, cursor_explicit_argrow = 0, 
    cursor_options = 0, value = 0, isnull = true, freeval = false, promise = PLPGSQL_PROMISE_NONE}
     $143 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 2, prev = 0x2ef83b0, name = 0x2ef8528 "found"}
  
  p *((PLpgSQL_var*)plpgsql_Datums[2])
  $149 = {
    dtype = PLPGSQL_DTYPE_VAR, dno = 2, refname = 0x2ef84f8 "found", 
    lineno = 0, isconst = false, notnull = false, default_val = 0x0, 
    datatype = 0x2ef83e8, cursor_explicit_expr = 0x0, cursor_explicit_argrow = 0, 
    cursor_options = 0, value = 0, isnull = true, freeval = false, promise = PLPGSQL_PROMISE_NONE}
	
	p *((PLpgSQL_var*)plpgsql_Datums[3])
  $19 = {
    dtype = PLPGSQL_DTYPE_REC, dno = 3, refname = 0x2f360e8 "row1", 
    lineno = 3, isconst = false, notnull = false, default_val = 0x0,
    datatype = 0x2f36018, cursor_explicit_expr = 0xffffffff00004004, 
    cursor_explicit_argrow = 0, cursor_options = 0, value = 9187201950435737470, 
    isnull = 8, freeval = false, promise = PLPGSQL_PROMISE_NONE}
    
  p *((PLpgSQL_var*)plpgsql_Datums[4])
  $20 = {
    dtype = PLPGSQL_DTYPE_REC, dno = 4, refname = 0x2f36320 "row2", 
    lineno = 4, isconst = false, notnull = false, default_val = 0x0,
    datatype = 0x2f36250, cursor_explicit_expr = 0xffffffff00004004, 
    cursor_explicit_argrow = 0, cursor_options = 0, value = 9187201950435737470, 
    isnull = 8, freeval = false, promise = PLPGSQL_PROMISE_NONE}
  
  p *((PLpgSQL_var*)plpgsql_Datums[5])
  $21 = {
    dtype = PLPGSQL_DTYPE_VAR, dno = 5, refname = 0x2f2d268 "txt1", 
    lineno = 5, isconst = false, notnull = false, default_val = 0x0,
    datatype = 0x2f2d158, cursor_explicit_expr = 0x0, 
    cursor_explicit_argrow = 0, cursor_options = 0, value = 0, isnull = true, 
    freeval = false, promise = PLPGSQL_PROMISE_NONE}
  
  p *((PLpgSQL_var*)plpgsql_Datums[6])
  $22 = {
    dtype = PLPGSQL_DTYPE_VAR, dno = 6, refname = 0x2f2daa0 "x1", 
    lineno = 6, isconst = false, notnull = false, default_val = 0x0, 
    datatype = 0x2f2d990, cursor_explicit_expr = 0x0, 
    cursor_explicit_argrow = 0, cursor_options = 0, value = 0, isnull = true, 
    freeval = false, promise = PLPGSQL_PROMISE_NONE}
    
  p *((PLpgSQL_var*)plpgsql_Datums[7])
  $23 = {
    dtype = PLPGSQL_DTYPE_VAR, dno = 7, refname = 0x2f2e460 "n1", 
    lineno = 7, isconst = false, notnull = false, default_val = 0x2f2e310, 
    datatype = 0x2f2e298, cursor_explicit_expr = 0x0, 
    cursor_explicit_argrow = 0, cursor_options = 0, value = 0,
    isnull = true, freeval = false, promise = PLPGSQL_PROMISE_NONE}

(gdb)  p *((PLpgSQL_var*)plpgsql_Datums[8])
$69 = {
  dtype = PLPGSQL_DTYPE_VAR, dno = 8, refname = 0x2f2c920 "sqlstate", 
  lineno = 12, isconst = true, notnull = false, 
  default_val = 0x0, datatype = 0x2f2c810, cursor_explicit_expr = 0x0, c
  ursor_explicit_argrow = 0, cursor_options = 0, value = 0, 
  isnull = true, freeval = false, promise = PLPGSQL_PROMISE_NONE}

(gdb)  p *((PLpgSQL_var*)plpgsql_Datums[9])
$70 = {
  dtype = PLPGSQL_DTYPE_VAR, dno = 9, refname = 0x2f2ca58 "sqlerrm", 
  lineno = 12, isconst = true, notnull = false,
  default_val = 0x0, datatype = 0x2f2c948, cursor_explicit_expr = 0x0, 
  cursor_explicit_argrow = 0, cursor_options = 0, value = 0, 
  isnull = true, freeval = false, promise = PLPGSQL_PROMISE_NONE}

p *((PLpgSQL_var*)plpgsql_Datums[10])
$25 = {
  dtype = PLPGSQL_DTYPE_RECFIELD, dno = 10, refname = 0x2f160c8 "c4", 
  lineno = 4, isconst = 255, notnull = 255, default_val = 0x1,
  datatype = 0x0, cursor_explicit_expr = 0x0, cursor_explicit_argrow = 2139062142, 
  cursor_options = 2139062143,value = 9187201950435737471, 
  isnull = 8, freeval = false, promise = PLPGSQL_PROMISE_NONE}

(gdb) p *((PLpgSQL_var*)plpgsql_Datums[11])
$29 = {
  dtype = PLPGSQL_DTYPE_RECFIELD, dno = 11, refname = 0x2f16260 "c4", 
  lineno = 3, isconst = 255, notnull = 255, default_val = 0x1,
  datatype = 0x0, cursor_explicit_expr = 0x0, cursor_explicit_argrow = 2139062142, 
  cursor_options = 2139062143, value = 9187201950435737471, 
  isnull = 8, freeval = false, promise = PLPGSQL_PROMISE_NONE}

2 执行

sql

======================================
PG
======================================
CREATE  OR REPLACE FUNCTION tfun1(p3 text, x3 int[]) RETURNS text AS $$
DECLARE
  row1 tf1%ROWTYPE;
  row2 tf1%ROWTYPE;
	txt1 text;
	x1 int[];
	n1 int := 1;
BEGIN

	RAISE NOTICE 'start division_by_zero n1';
	n1 = n1 / 0;
  EXCEPTION
    WHEN division_by_zero THEN
        RAISE NOTICE 'caught division_by_zero do nothing';
  
	RAISE NOTICE 'start print x1';
  FOREACH x1 SLICE 1 IN ARRAY $2
  LOOP
    RAISE NOTICE 'row = %', x1;
  END LOOP;	

  RAISE NOTICE 'start connecting c4';
	txt1 = p3 || ':';
    FOR row1 IN SELECT * FROM tf1 WHERE c3 = p3
	LOOP
		row2.c4 = row1.c4;
		txt1 = txt1 || row2.c4 ||'+';
	END LOOP;
	return txt1;
END;
$$ LANGUAGE plpgsql;

select tfun1('China', ARRAY[[1,2,3],[4,5,6],[7,8,9],[10,11,12]]);

上面SQL对应的执行顺序

plpgsql_call_handler
  plpgsql_exec_function
    exec_toplevel_block
      exec_stmt_block
        TRY
          exec_stmts
            ...
            case PLPGSQL_STMT_RAISE:
              rc = exec_stmt_raise(estate, (PLpgSQL_stmt_raise *) stmt)			： RAISE NOTICE 'start division_by_zero n1';
            case PLPGSQL_STMT_ASSIGN:
              rc = exec_stmt_assign(estate, (PLpgSQL_stmt_assign *) stmt)		：n1 = n1 / 0;
        PG_CATCH
          /* Look for a matching exception handler */
          foreach(e, block->exceptions->exc_list)
             if (exception_matches_conditions(edata, exception->conditions))
               exec_stmts(estate, exception->action)
                 ...
                 case PLPGSQL_STMT_RAISE:
                   rc = exec_stmt_raise(estate, (PLpgSQL_stmt_raise *) stmt)	：RAISE NOTICE 'caught division_by_zero do nothing';
                                                                          		：RAISE NOTICE 'start print x1';             
                 case PLPGSQL_STMT_FOREACH_A:
                   rc = exec_stmt_foreach_a(estate, (PLpgSQL_stmt_foreach_a *) stmt)	：FOREACH
                     exec_stmts															：RAISE NOTICE 'row = %', x1;

                 case PLPGSQL_STMT_RAISE:
                   rc = exec_stmt_raise(estate, (PLpgSQL_stmt_raise *) stmt)	：RAISE NOTICE 'start connecting c4';
                 case PLPGSQL_STMT_ASSIGN:
                   rc = exec_stmt_assign(estate, (PLpgSQL_stmt_assign *) stmt)	：txt1 = p3 || ':';
                 case PLPGSQL_STMT_FORS:
                   rc = exec_stmt_fors(estate, (PLpgSQL_stmt_fors *) stmt)		：FOR xxx IN
                     exec_stmts													：row2.c4 = row1.c4;
																				：txt1 = txt1 || row2.c4 ||'+';
                 case PLPGSQL_STMT_RETURN：
                   rc = exec_stmt_return(estate, (PLpgSQL_stmt_return *) stmt)
        PG_END_TRY

这就是一个plpgsql编译执行的全流程。