总结

数组赋值

• 如果是默认值数组
  • 编译时只组装expr出来记录ARRAY[1,2,3,4,5]
  • 在执行赋默认值时走执行器把expr变成value记录到datum中
    • 执行时语义解析阶段就会把只拼出来：transformArrayExpr将ARRAY[1,2,3,4,5]转换为ArrayExpr
    • 执行时ExecEvalExpr阶段只当做Const把Value赋值给Datum即可。
• 如果是传入数组，直接当做常量赋值即可。

数组取值

• 取值阶段即调用SPI执行"x = arr[3];"语句的过程，注意赋值逻辑全部交给PG执行器，PL只给回调用于查询变量。
• 执行器会回调pl函数找到x和arr，然后走ExecEvalExpr把数组指定的值赋给x。

用例

DO $$
DECLARE
  arr int[] := ARRAY[1,2,3,4,5];
  x int;
BEGIN
  x = arr[3];
  raise notice '%', x;
-- 编译后、执行前：变量状态
$6 = {dtype = PLPGSQL_DTYPE_VAR, dno = 0, refname = 0x2b1e3c0 "found", 
  lineno = 0, isconst = false, notnull = false, default_val = 0x0, datatype = 0x2b1e2c8, 
  cursor_explicit_expr = 0x0, cursor_explicit_argrow = 0, cursor_options = 0, 
  value = 0, isnull = true, freeval = false, promise = PLPGSQL_PROMISE_NONE}
$7 = {dtype = PLPGSQL_DTYPE_VAR, dno = 1, refname = 0x2b1f1c0 "arr", 
  lineno = 3, isconst = false, notnull = false, default_val = 0x2b1f070, datatype = 0x2b1eff0, 
  cursor_explicit_expr = 0x0, cursor_explicit_argrow = 0, cursor_options = 0, 
  value = 0, isnull = true, freeval = false, promise = PLPGSQL_PROMISE_NONE}
$8 = {dtype = PLPGSQL_DTYPE_VAR, dno = 2, refname = 0x2b1fa40 "x", 
  lineno = 4, isconst = false, notnull = false, default_val = 0x0, datatype = 0x2b1f948, 
  cursor_explicit_expr = 0x0, cursor_explicit_argrow = 0, cursor_options = 0, 
  value = 0, isnull = true, freeval = false, promise = PLPGSQL_PROMISE_NONE}

【如何赋值】DECLARE BLOCK初始值赋值（exec_stmt_block）

arr int[] := ARRAY[1,2,3,4,5];

（为什么进入BLOCK每次都要走一遍赋初值流程？哪里决定的哪些变量需要赋值？ 《Postgresql源码（79）plpgsql中多层调用时参数传递关键点分析（pl参数）》 ：问题五）

同样是走assign_simple_var统一赋值入口给arr赋值

exec_stmt_block
  // 两个值都是VAR类型，所以都需要初始化赋默认值
  for (i = 0; i < block->n_initvars; i++)
    case PLPGSQL_DTYPE_VAR:
      // 先给0
      assign_simple_var(estate, var, (Datum) 0, true, false);
      // 如果有默认值，在给默认值
      exec_assign_expr(estate, (PLpgSQL_datum *) var, var->default_val);

arr有默认值进入exec_assign_expr

exec_assign_expr
  exec_prepare_plan
    SPI_prepare_extended
      _SPI_prepare_plan      // 完成 语法解析、语义解析
        raw_parser           // src=0x2b1bd30 "ARRAY[1,2,3,4,5]"
// 语法树：SelectStmt={targetList = 0x2b1d640}
//   targetList   =[{ResTarget}]
//   ResTarget    ={val = A_ArrayExpr}
//   A_ArrayExpr  ={type = T_A_ArrayExpr, elements = 0x2b1d4b0, location = 0}
//   elements     =[{A_Const},{A_Const},{A_Const},{A_Const},{A_Const}]
        pg_analyze_and_rewrite_withcb
          parse_analyze_withcb
            plpgsql_parser_setup      // 挂上从PL拿变量的钩子
            transformTopLevelStmt
              transformOptionalSelectInto
                transformStmt
                  【case T_SelectStmt】
                    transformSelectStmt
                      transformTargetList
                        transformTargetEntry
                          transformExpr
                            transformExprRecurse   // 传入：expr=A_ArrayExpr
                              【case T_A_ArrayExpr】
                                transformArrayExpr
                                  // 根据A_ArrayExpr拼接一个ArrayExpr结构返回
// ArrayExpr= {xpr = {type = T_ArrayExpr}, array_typeid = 1007, array_collid = 0, element_typeid = 23, elements = 0x2b1dc70, multidims = false, location = 0}
// elements = [{Const},{Const},{Const},{Const},{Const}]
        pg_analyze_and_rewrite_withcb：完成
      _SPI_prepare_plan：完成
    SPI_prepare_extended：完成
返回plan中plancache_list记录了转换后的ArrayExpr
// {magic = 569278163, saved = false, oneshot = false, plancache_list = 0x2b283d8, plancxt = 0x2b28270, parse_mode = RAW_PARSE_PLPGSQL_EXPR, cursor_options = 0, nargs = 0, argtypes = 0x0, parserSetup = 0x7fd83131cfec <plpgsql_parser_setup>, parserSetupArg = 0x2b1bca0}
  exec_eval_expr
    // 进入时：PLpgSQL_expr = {query = 0x2b1dd40 "ARRAY[1,2,3,4,5]", parseMode = RAW_PARSE_PLPGSQL_EXPR...}
    exec_eval_simple_expr
      ExecEvalExpr
        state->evalfunc
          ExecInterpExprStillValid
            ExecJustConst

ARRAY在编译阶段已经做好了放在default_val中，这里只是一个简单的常量赋值，没有发现数组拼接构造的逻辑。

$7 = {dtype = PLPGSQL_DTYPE_VAR, dno = 1, refname = 0x2b1f1c0 "arr", 
  lineno = 3, isconst = false, notnull = false, default_val = 0x2b1f070, datatype = 0x2b1eff0, 
  cursor_explicit_expr = 0x0, cursor_explicit_argrow = 0, cursor_options = 0, 
  value = 0, isnull = true, freeval = false, promise = PLPGSQL_PROMISE_NONE}

编译生成default_val

编译阶段是怎么处理生成default_val的：plpgsql_compile_inline编译 arr int[] := ARRAY[1,2,3,4,5];

第一步：处理类型 int[] ：decl_datatype识别 int[] 返回PLpgSQL_type

arr int[] := ARRAY[1,2,3,4,5]
    T_WORD
decl_datatype	:
						 * If there's a lookahead token, read_datatype
						 * should consume it.
						$$ = read_datatype(yychar);
						yyclearin;
read_datatype
  char *dtname = yylval.word.ident; // dtname = "int"
  // while (tok != ';')
  tok = yylex();                    // 91 -> [
  tok = yylex();                    // 93 -> ]
  tok = yylex();                    // 270 -> COLON_EQUALS
  // 取出完整typename = int[]
  result = parse_datatype(type_name, startlocation)
  return result;

第二步：读取默认值

decl_defval		: ';'
					{ $$ = NULL; }
				| decl_defkey
						$$ = read_sql_expression(';', ";");
decl_defkey		: assign_operator
				| K_DEFAULT 
read_sql_expression
  read_sql_construct(until=59 ";", until2=0, until3=0, expected=0x7fd83134458c ";",
                     parsemode=RAW_PARSE_PLPGSQL_EXPR, isexpression=true, 
                     valid_sql=true, trim=true, startloc=0x0, endtoken=0x0)
    // 全部工作就是
    // 【1】拼一个PLpgSQL_expr
    // 【2】check_sql_expr检查正确性（过一遍raw_parser即可）
    {query = 0x2b1bd30 "ARRAY[1,2,3,4,5]", parseMode = RAW_PARSE_PLPGSQL_EXPR, plan = 0x0, 
     paramnos = 0x0, func = 0x0, ns = 0x2b1b038, 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}

【如何取值】数组取值给普通变量

x = arr[3];

exec_stmt_assign
  exec_assign_expr
    exec_assign_expr
      阶段一：exec_prepare_plan
      阶段二：exec_eval_expr

阶段一：exec_prepare_plan

正常执行到exec_stmt_assign开始赋值，还是在语义分析的时候回调取值

exec_stmt_assign
  exec_assign_expr
    exec_assign_expr
      exec_prepare_plan
        SPI_prepare_extended
          _SPI_prepare_plan
            pg_analyze_and_rewrite_withcb
              parse_analyze_withcb
                transformTopLevelStmt
                  transformOptionalSelectInto
                    transformStmt
                      transformPLAssignStmt
                        transformTargetList
                          transformTargetEntry
                            transformExpr
                              transformExprRecurse
                                transformIndirection
                                  transformExprRecurse
                                    transformColumnRef
                                      plpgsql_post_column_ref
                                        resolve_column_ref
                                          make_datum_param                    // 拼一个Param返回

plpgsql_post_column_ref回调函数都做了什么？

第一步：make_datum_param

由datum:

PLpgSQL_var = {
 dtype = PLPGSQL_DTYPE_VAR, dno = 1, refname = 0x2b13db0 "arr", lineno = 3, 
 isconst = false, notnull = false, default_val = 0x2b13c60, datatype = 0x2b13be0, 
 cursor_explicit_expr = 0x0, cursor_explicit_argrow = 0, cursor_options = 0, 
 value = 44332064, isnull = false, freeval = true, promise = PLPGSQL_PROMISE_NONE}

生成Param，注意paramid=dno+1

Param = {
  xpr = {type = T_Param}, paramkind = PARAM_EXTERN, paramid = 2, 
  paramtype = 1007, paramtypmod = -1, paramcollid = 0, location = 4}

返回的Param只记录了paramid=2表示dno=1，和类型信息。

阶段二：exec_eval_expr

exec_stmt_assign
  exec_assign_expr
    exec_eval_expr
      exec_eval_simple_expr
        ExecInitExprWithParams
          ExecInitExprRec
            ExecInitSubscriptingRef
              ExecInitExprRec
                plpgsql_param_compile
                  // 给执行器配一个合适的取值函数
                  scratch.d.cparam.paramfunc = plpgsql_param_eval_var_ro;
        ExecEvalExpr
          ExecInterpExprStillValid
            ExecInterpExpr