Postgresql使用plpgsql解析游标定义子树的过程

Postgresql使用plpgsql解析游标定义子树的过程

例如有如下函数

create or replace procedure fun1(a in integer) as $$
declarecur cursor for select * from t10 order by f1;

end;
$$ LANGUAGE plpgsql ;

声明中游标是怎么解析的？

cur cursor for select * from t10 order by f1;

step1

语法树

decl_statement	: decl_varname decl_const decl_datatype decl_collate decl_notnull decl_defval{...}
/* 【第一步】 */
/* 执行到这里的时候decl_varname、opt_scrollable都解析完了 */
/* decl_varname只检查名字有没有使用过，不加入namespace */
/* opt_scrollable do nothing */| decl_varname opt_scrollable K_CURSOR{ plpgsql_ns_push($1.name, PLPGSQL_LABEL_OTHER); }
/* 这里加入namespace
$7 = {itemtype = PLPGSQL_NSTYPE_LABEL, itemno = 3, prev = 0x381ad50, name = 0x381add8 "cur"}
$2 = {itemtype = PLPGSQL_NSTYPE_LABEL, itemno = 0, prev = 0x381ad18, name = 0x381ad60 ""}
$3 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 1, prev = 0x381ac48, name = 0x381ad28 "found"}
$4 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 0, prev = 0x381ac10, name = 0x381ac58 "a_int"}
$5 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 0, prev = 0x381ab40, name = 0x381ac20 "$1"}
$6 = {itemtype = PLPGSQL_NSTYPE_LABEL, itemno = 0, prev = 0x0, name = 0x381ab50 "demo10"}
*//* 解析后面的语句先要递归完成decl_cursor_args、decl_is_for、decl_cursor_query */
/* goto decl_cursor_args 继续阅读 */decl_cursor_args decl_is_for decl_cursor_query{...plpgsql_ns_pop();...plpgsql_build_variable();...}

step2

decl_cursor_args
检查是普通语法还是复杂语法
curs2 CURSOR FOR SELECT * FROM tenk1;
curs3 CURSOR (key integer) FOR SELECT * FROM tenk1 WHERE unique1 = key;

当前语句cur cursor for select * from t10 order by f1;属于简单语法

语法树

/* 【第二步】 */
decl_cursor_args :{$$ = NULL;}| '(' decl_cursor_arglist ')'{PLpgSQL_row *new;int i;ListCell *l;new = palloc0(sizeof(PLpgSQL_row));new->dtype = PLPGSQL_DTYPE_ROW;new->refname = "(unnamed row)";new->lineno = plpgsql_location_to_lineno(@1);new->rowtupdesc = NULL;new->nfields = list_length($2);new->fieldnames = palloc(new->nfields * sizeof(char *));new->varnos = palloc(new->nfields * sizeof(int));i = 0;foreach (l, $2){PLpgSQL_variable *arg = (PLpgSQL_variable *) lfirst(l);Assert(!arg->isconst);new->fieldnames[i] = arg->refname;new->varnos[i] = arg->dno;i++;}list_free($2);plpgsql_adddatum((PLpgSQL_datum *) new);$$ = (PLpgSQL_datum *) new;};

step3

decl_cursor_query

decl_cursor_query :{$$ = read_sql_stmt();
/*
read_sql_construct(';', 0, 0, ";", RAW_PARSE_DEFAULT,false, true, true, NULL, NULL);for (;;)tok = yylex()     275      T_WORD   selecttok = yylex()     42       *        *tok = yylex()     325      K_FROM   fromtok = yylex()     275      T_WORD   t10tok = yylex()     275      T_WORD   ordertok = yylex()     288      K_BY     bytok = yylex()     275      T_WORD   f1tok = yylex()     59       ;        ;return{query = 0x381b330 "select * from t10 order by f1", parseMode = RAW_PARSE_DEFAULT, plan = 0x0, paramnos = 0x0, func = 0x0, ns = 0x381adc8, 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}
*/};

step4

语法树，从【第四步】开始看

注意在第一步Push进去的cur
plpgsql_ns_push($1.name, PLPGSQL_LABEL_OTHER)
在第四步开始就Pop出来了，这个符号主要是给decl_cursor_args、decl_is_for、decl_cursor_query使用的

decl_statement	: decl_varname decl_const decl_datatype decl_collate decl_notnull decl_defval{...}
/* 【第一步】 */
/* 执行到这里的时候decl_varname、opt_scrollable都解析完了 */
/* decl_varname只检查名字有没有使用过，不加入namespace */
/* opt_scrollable do nothing */| decl_varname opt_scrollable K_CURSOR{ plpgsql_ns_push($1.name, PLPGSQL_LABEL_OTHER); }
/* 这里加入namespace
$7 = {itemtype = PLPGSQL_NSTYPE_LABEL, itemno = 3, prev = 0x381ad50, name = 0x381add8 "cur"}
$2 = {itemtype = PLPGSQL_NSTYPE_LABEL, itemno = 0, prev = 0x381ad18, name = 0x381ad60 ""}
$3 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 1, prev = 0x381ac48, name = 0x381ad28 "found"}
$4 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 0, prev = 0x381ac10, name = 0x381ac58 "a_int"}
$5 = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 0, prev = 0x381ab40, name = 0x381ac20 "$1"}
$6 = {itemtype = PLPGSQL_NSTYPE_LABEL, itemno = 0, prev = 0x0, name = 0x381ab50 "demo10"}
*//* 解析后面的语句先要递归完成decl_cursor_args、decl_is_for、decl_cursor_query */
/* goto decl_cursor_args 继续阅读 */
/* 【第四步】 */decl_cursor_args decl_is_for decl_cursor_query{...plpgsql_ns_pop();...// 下面函数说明中解释new = (PLpgSQL_var *) plpgsql_build_variable(...plpgsql_build_datatype()...);...curname_def = palloc0(sizeof(PLpgSQL_expr));/* 注意new已经在plpgsql_Datums数组中了，最后不需要返回 */
/* 下面在做一些调整，就可以结束了 *//* Note: refname has been truncated to NAMEDATALEN */cp1 = new->refname;cp2 = buf;/** Don't trust standard_conforming_strings here;* it might change before we use the string.*/if (strchr(cp1, '\') != NULL)*cp2++ = ESCAPE_STRING_SYNTAX;*cp2++ = ''';while (*cp1){if (SQL_STR_DOUBLE(*cp1, true))*cp2++ = *cp1;*cp2++ = *cp1++;}strcpy(cp2, "'::fcursor");curname_def->query = pstrdup(buf);curname_def->parseMode = RAW_PARSE_PLPGSQL_EXPR;new->default_val = curname_def;new->cursor_explicit_expr = $7;if ($5 == NULL)new->cursor_explicit_argrow = -1;elsenew->cursor_explicit_argrow = $5->dno;new->cursor_options = CURSOR_OPT_FAST_PLAN | $2;};

函数说明

plpgsql_build_datatype

系统表查询类型OID，构造PLpgSQL_type

PLpgSQL_type *
plpgsql_build_datatype(Oid typeOid, int32 typmod,Oid collation, TypeName *origtypname)
{HeapTuple	typeTup;PLpgSQL_type *typ;typeTup = SearchSysCache1(TYPEOID, ObjectIdGetDatum(typeOid));if (!HeapTupleIsValid(typeTup))elog(ERROR, "cache lookup failed for type %u", typeOid);typ = build_datatype(typeTup, typmod, collation, origtypname);ReleaseSysCache(typeTup);return typ;
}

本例中oid

postgres=# select * from pg_type where oid = 1790;
-[ RECORD 1 ]--+----------
oid            | 1790
typname        | refcursor
typnamespace   | 11
typowner       | 10
typlen         | -1
typbyval       | f
typtype        | b
typcategory    | U
typispreferred | f
typisdefined   | t
typdelim       | ,
typrelid       | 0
typsubscript   | -
typelem        | 0
typarray       | 2201
typinput       | textin
typoutput      | textout
typreceive     | textrecv
typsend        | textsend

返回

$18 = {typname = 0x381a660 "refcursor", typoid = 1790, ttype = PLPGSQL_TTYPE_SCALAR, typlen = -1, typbyval = false, typtype = 98 'b', collation = 0, typisarray = false, atttypmod = -1, origtypname = 0x0, tcache = 0x0, tupdesc_id = 0}

plpgsql_build_variable

拼一个PLpgSQL_variable记录到plpgsql_Datums，然后返回

PLpgSQL_variable *
plpgsql_build_variable(const char *refname, int lineno, PLpgSQL_type *dtype,bool add2namespace)
{PLpgSQL_variable *result;switch (dtype->ttype){case PLPGSQL_TTYPE_SCALAR:{/* Ordinary scalar datatype */PLpgSQL_var *var;var = palloc0(sizeof(PLpgSQL_var));var->dtype = PLPGSQL_DTYPE_VAR;var->refname = pstrdup(refname);var->lineno = lineno;var->datatype = dtype;/* other fields are left as 0, might be changed by caller *//* preset to NULL */var->value = 0;var->isnull = true;var->freeval = false;plpgsql_adddatum((PLpgSQL_datum *) var);
/*
变量是一定要加到plpgsql_Datums中的：(gdb) p plpgsql_nDatums
$19 = 3(gdb) p *((PLpgSQL_var*)plpgsql_Datums[2])
$21 = {dtype = PLPGSQL_DTYPE_VAR, dno = 2, refname = 0x381b458 "cur", lineno = 3, isconst = false, notnull = false, default_val = 0x0, datatype = 0x381b368, cursor_explicit_expr = 0x0, cursor_explicit_argrow = 0, cursor_options = 0, value = 0, isnull = true, freeval = false, promise = PLPGSQL_PROMISE_NONE}
*/if (add2namespace)plpgsql_ns_additem(PLPGSQL_NSTYPE_VAR,var->dno,refname);
/*
变量也需要增加到ns_top中
2: *ns_top = {itemtype = PLPGSQL_NSTYPE_VAR, itemno = 2, prev = 0x381ad50, name = 0x381b488 "cur"}
*/result = (PLpgSQL_variable *) var;break;}case PLPGSQL_TTYPE_REC:{/* Composite type -- build a record variable */PLpgSQL_rec *rec;rec = plpgsql_build_record(refname, lineno,dtype, dtype->typoid,add2namespace);result = (PLpgSQL_variable *) rec;break;}case PLPGSQL_TTYPE_PSEUDO:ereport(ERROR,(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),errmsg("variable "%s" has pseudo-type %s",refname, format_type_be(dtype->typoid))));result = NULL;		/* keep compiler quiet */break;default:elog(ERROR, "unrecognized ttype: %d", dtype->ttype);result = NULL;		/* keep compiler quiet */break;}return result;
}

注意union中复合变量的使用

注意在使用yacc的union内的结构体时，要注意格式，例如

%union {core_YYSTYPE			core_yystype;...struct varname{char *name;int  lineno;}						varname;...
}%type <varname> decl_varname// 在构造decl_varname时，返回值注意要使用结构体内的变量名
decl_varname	: T_WORD$$.name = $1.ident;$$.lineno = plpgsql_location_to_lineno(@1);...// 在作为变量使用时，也要注意使用结构体内的变量名
decl_cursor_name:K_CURSOR decl_varname opt_scrollable{plpgsql_ns_push($2.name, PLPGSQL_LABEL_OTHER);$$.name = $2;$$.scrollopt = $3;}...