Java教程
04-PG数据库的语法解析
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PG数据库的语法解析
一、gram.y词法解析
src\backend\parser\gram.y文件中讲解了词法解析器。
%{
Declarations
%}
Definitions
%%
Productions
%%
User subroutines
在词法解析器中，我们讲到的.y文件的知识点，这一篇文章主要讲解PG中是如何使用的词法解析器的。
1、Declarations
包含的头文件，定义后文使用的函数，定义宏和别名。这部分为C代码，不做具体介绍。
2、Definitions
Definitions在Bison的作用与Flex中的功能也差不多,在这个段定义一些Bison专有变量或相关选项.
%purge-parser
指示Bison创建一个可重入的解析器.与普通的解析器一个很大的不同的,yylval的类型是union指针而不是union.
%expect
%expect N告诉Bison，解析器应该有N个shift/reduce冲突，如果不匹配，Bison将报告编译时错误。
%name-prefix
命名函数名称,默认为yy
%name-prefix “base_yy”意味着默认的yyxx()会变成base_yyxx().比如yyparse(),yylex(),yyerror(),yylval,yychar和
yydebug.
%locations
位置
%parse-param
%parse-param声明的内容位于yyparse()的括号之间,可以声明任意多的参数.
比如%parse-param {core_yyscan_t yyscanner},参数为core_yyscan_t yyscanner.
%lex-param
%lex-param声明的内容位于yylex()的括号之间,可以声明任意多的参数.
比如%lex-param {core_yyscan_t yyscanner},参数为core_yyscan_t yyscanner.
%union
%union声明了在解析器中标识符所使用的类型.
Bison解析器,每一个标识符,包括tokens和非终结符,都有值与之关联,默认的,值的类型都是整型,但在实际应用中远远不够.
%union可以为标识符值创建C语言union声明.
%union{
core_YYSTYPE core_yystype; /* these fields must match core_YYSTYPE: */
int ival;
char *str;
const char *keyword;
...
}
其中core_yystype的类型为core_YYSTYPE联合体.
/* * The scanner returns extra data about scanned tokens in this union type. * Note that this is a subset of the fields used in YYSTYPE of the bison * parsers built atop the scanner. */
typedef union core_YYSTYPE{
int ival; /* for integer literals */
char *str; /* for identifiers and non- integer literals */
const char *keyword; /* canonical spelling of keywords */
} core_YYSTYPE;
一旦定义了union,那需要通过将union中合适的名称放在尖括号(<>)中,用以告诉Bison哪些符号具有哪些类型的值.
%type
类型定义,如:
%type <node> stmt schema_stmt AlterEventTrigStmt AlterCollationStmt ...
表示标识符/非终结符 的类型可以是stmt/schema_stmt/AlterEventTrigStmt/…
%nonassoc
使用%nonassoc声明非关联操作符。
%left
左关联操作符
%right
右关联操作符
3、Productions
按照根节点依次对表达式进行解析，最终将结果汇集到根节点。
**stmtblock：**语法块根节点
/*
* The target production for the whole parse.
*/
stmtblock: stmtmulti
{
pg_yyget_extra(yyscanner)->parsetree = $1;
}
;
**stmt：**所有类型的节点
stmt :
AlterEventTrigStmt
| AlterCollationStmt
| AlterDatabaseStmt
| AlterDatabaseSetStmt
| AlterDefaultPrivilegesStmt
| AlterDomainStmt
| AlterEnumStmt
| AlterExtensionStmt
| AlterExtensionContentsStmt
| AlterFdwStmt
| AlterForeignServerStmt
| AlterForeignTableStmt
| AlterFunctionStmt
| AlterGroupStmt
| AlterObjectDependsStmt
| AlterObjectSchemaStmt
| AlterOwnerStmt
| AlterOperatorStmt
| AlterPolicyStmt
| AlterSeqStmt
| AlterSystemStmt
| AlterTableStmt
| AlterTblSpcStmt
| AlterCompositeTypeStmt
| AlterPublicationStmt
| AlterRoleSetStmt
| AlterRoleStmt
| AlterSubscriptionStmt
| AlterTSConfigurationStmt
| AlterTSDictionaryStmt
| AlterUserMappingStmt
| AnalyzeStmt
| CallStmt
| CheckPointStmt
| ClosePortalStmt
| ClusterStmt
| CommentStmt
| ConstraintsSetStmt
| CopyStmt
| CreateAmStmt
| CreateAsStmt
| CreateAssertionStmt
| CreateCastStmt
| CreateConversionStmt
| CreateDomainStmt
| CreateExtensionStmt
| CreateFdwStmt
| CreateForeignServerStmt
| CreateForeignTableStmt
| CreateFunctionStmt
| CreateGroupStmt
| CreateMatViewStmt
| CreateOpClassStmt
| CreateOpFamilyStmt
| CreatePublicationStmt
| AlterOpFamilyStmt
| CreatePolicyStmt
| CreatePLangStmt
| CreateSchemaStmt
| CreateSeqStmt
| CreateStmt
| CreateSubscriptionStmt
| CreateStatsStmt
| CreateTableSpaceStmt
| CreateTransformStmt
| CreateTrigStmt
| CreateEventTrigStmt
| CreateRoleStmt
| CreateUserStmt
| CreateUserMappingStmt
| CreatedbStmt
| DeallocateStmt
| DeclareCursorStmt
| DefineStmt
| DeleteStmt
| DiscardStmt
| DoStmt
| DropCastStmt
| DropOpClassStmt
| DropOpFamilyStmt
| DropOwnedStmt
| DropPLangStmt
| DropStmt
| DropSubscriptionStmt
| DropTableSpaceStmt
| DropTransformStmt
| DropRoleStmt
| DropUserMappingStmt
| DropdbStmt
| ExecuteStmt
| ExplainStmt
| FetchStmt
| GrantStmt
| GrantRoleStmt
| ImportForeignSchemaStmt
| IndexStmt
| InsertStmt
| ListenStmt
| RefreshMatViewStmt
| LoadStmt
| LockStmt
| NotifyStmt
| PrepareStmt
| ReassignOwnedStmt
| ReindexStmt
| RemoveAggrStmt
| RemoveFuncStmt
| RemoveOperStmt
| RenameStmt
| RevokeStmt
| RevokeRoleStmt
| RuleStmt
| SecLabelStmt
| SelectStmt
| TransactionStmt
| TruncateStmt
| UnlistenStmt
| UpdateStmt
| VacuumStmt
| VariableResetStmt
| VariableSetStmt
| VariableShowStmt
| ViewStmt
| /*EMPTY*/
{ $$ = NULL; }
;
**a_expr:**末端表达式解析
/*
* General expressions
* This is the heart of the expression syntax.
*
* We have two expression types: a_expr is the unrestricted kind, and
* b_expr is a subset that must be used in some places to avoid shift/reduce
* conflicts. For example, we can't do BETWEEN as "BETWEEN a_expr AND a_expr"
* because that use of AND conflicts with AND as a boolean operator. So,
* b_expr is used in BETWEEN and we remove boolean keywords from b_expr.
*
* Note that '(' a_expr ')' is a b_expr, so an unrestricted expression can
* always be used by surrounding it with parens.
*
* c_expr is all the productions that are common to a_expr and b_expr;
* it's factored out just to eliminate redundant coding.
*
* Be careful of productions involving more than one terminal token.
* By default, bison will assign such productions the precedence of their
* last terminal, but in nearly all cases you want it to be the precedence
* of the first terminal instead; otherwise you will not get the behavior
* you expect! So we use %prec annotations freely to set precedences.
*/
a_expr: c_expr { $$ = $1; }
| a_expr TYPECAST Typename
{ $$ = makeTypeCast($1, $3, @2); }
| a_expr COLLATE any_name
{
CollateClause *n = makeNode(CollateClause);
n->arg = $1;
n->collname = $3;
n->location = @2;
$$ = (Node *) n;
}
| a_expr AT TIME ZONE a_expr %prec AT
{
$$ = (Node *) makeFuncCall(SystemFuncName("timezone"),
list_make2($5, $1),
@2);
}
/*
* These operators must be called out explicitly in order to make use
* of bison's automatic operator-precedence handling. All other
* operator names are handled by the generic productions using "Op",
* below; and all those operators will have the same precedence.
*
* If you add more explicitly-known operators, be sure to add them
* also to b_expr and to the MathOp list below.
*/
| '+' a_expr %prec UMINUS
{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "+", NULL, $2, @1); }
| '-' a_expr %prec UMINUS
{ $$ = doNegate($2, @1); }
| a_expr '+' a_expr
{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "+", $1, $3, @2); }
| a_expr '-' a_expr
{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "-", $1, $3, @2); }
| a_expr '*' a_expr
{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "*", $1, $3, @2); }
| a_expr '/' a_expr
{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "/", $1, $3, @2); }
| a_expr '%' a_expr
{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "%", $1, $3, @2); }
| a_expr '^' a_expr
{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "^", $1, $3, @2); }
| a_expr '<' a_expr
{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "<", $1, $3, @2); }
| a_expr '>' a_expr
{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, ">", $1, $3, @2); }
| a_expr '=' a_expr
{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "=", $1, $3, @2); }
| a_expr LESS_EQUALS a_expr
{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "<=", $1, $3, @2); }
| a_expr GREATER_EQUALS a_expr
{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, ">=", $1, $3, @2); }
| a_expr NOT_EQUALS a_expr
{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "<>", $1, $3, @2); }
| a_expr qual_Op a_expr %prec Op
{ $$ = (Node *) makeA_Expr(AEXPR_OP, $2, $1, $3, @2); }
| qual_Op a_expr %prec Op
{ $$ = (Node *) makeA_Expr(AEXPR_OP, $1, NULL, $2, @1); }
| a_expr qual_Op %prec POSTFIXOP
{ $$ = (Node *) makeA_Expr(AEXPR_OP, $2, $1, NULL, @2); }
| a_expr AND a_expr
{ $$ = makeAndExpr($1, $3, @2); }
| a_expr OR a_expr
{ $$ = makeOrExpr($1, $3, @2); }
| NOT a_expr
{ $$ = makeNotExpr($2, @1); }
| NOT_LA a_expr %prec NOT
{ $$ = makeNotExpr($2, @1); }
| a_expr LIKE a_expr
{
$$ = (Node *) makeSimpleA_Expr(AEXPR_LIKE, "~~",
$1, $3, @2);
}
| a_expr LIKE a_expr ESCAPE a_expr %prec LIKE
{
FuncCall *n = makeFuncCall(SystemFuncName("like_escape"),
list_make2($3, $5),
@2);
$$ = (Node *) makeSimpleA_Expr(AEXPR_LIKE, "~~",
$1, (Node *) n, @2);
}
| a_expr NOT_LA LIKE a_expr %prec NOT_LA
{
$$ = (Node *) makeSimpleA_Expr(AEXPR_LIKE, "!~~",
$1, $4, @2);
}
| a_expr NOT_LA LIKE a_expr ESCAPE a_expr %prec NOT_LA
{
FuncCall *n = makeFuncCall(SystemFuncName("like_escape"),
list_make2($4, $6),
@2);
$$ = (Node *) makeSimpleA_Expr(AEXPR_LIKE, "!~~",
$1, (Node *) n, @2);
}
| a_expr ILIKE a_expr
{
$$ = (Node *) makeSimpleA_Expr(AEXPR_ILIKE, "~~*",
$1, $3, @2);
}
| a_expr ILIKE a_expr ESCAPE a_expr %prec ILIKE
{
FuncCall *n = makeFuncCall(SystemFuncName("like_escape"),
list_make2($3, $5),
@2);
$$ = (Node *) makeSimpleA_Expr(AEXPR_ILIKE, "~~*",
$1, (Node *) n, @2);
}
| a_expr NOT_LA ILIKE a_expr %prec NOT_LA
{
$$ = (Node *) makeSimpleA_Expr(AEXPR_ILIKE, "!~~*",
$1, $4, @2);
}
| a_expr NOT_LA ILIKE a_expr ESCAPE a_expr %prec NOT_LA
{
FuncCall *n = makeFuncCall(SystemFuncName("like_escape"),
list_make2($4, $6),
@2);
$$ = (Node *) makeSimpleA_Expr(AEXPR_ILIKE, "!~~*",
$1, (Node *) n, @2);
}
| a_expr SIMILAR TO a_expr %prec SIMILAR
{
FuncCall *n = makeFuncCall(SystemFuncName("similar_escape"),
list_make2($4, makeNullAConst(-1)),
@2);
$$ = (Node *) makeSimpleA_Expr(AEXPR_SIMILAR, "~",
$1, (Node *) n, @2);
}
| a_expr SIMILAR TO a_expr ESCAPE a_expr %prec SIMILAR
{
FuncCall *n = makeFuncCall(SystemFuncName("similar_escape"),
list_make2($4, $6),
@2);
$$ = (Node *) makeSimpleA_Expr(AEXPR_SIMILAR, "~",
$1, (Node *) n, @2);
}
| a_expr NOT_LA SIMILAR TO a_expr %prec NOT_LA
{
FuncCall *n = makeFuncCall(SystemFuncName("similar_escape"),
list_make2($5, makeNullAConst(-1)),
@2);
$$ = (Node *) makeSimpleA_Expr(AEXPR_SIMILAR, "!~",
$1, (Node *) n, @2);
}
| a_expr NOT_LA SIMILAR TO a_expr ESCAPE a_expr %prec NOT_LA
{
FuncCall *n = makeFuncCall(SystemFuncName("similar_escape"),
list_make2($5, $7),
@2);
$$ = (Node *) makeSimpleA_Expr(AEXPR_SIMILAR, "!~",
$1, (Node *) n, @2);
}
/* NullTest clause
* Define SQL-style Null test clause.
* Allow two forms described in the standard:
* a IS NULL
* a IS NOT NULL
* Allow two SQL extensions
* a ISNULL
* a NOTNULL
*/
| a_expr IS NULL_P %prec IS
{
NullTest *n = makeNode(NullTest);
n->arg = (Expr *) $1;
n->nulltesttype = IS_NULL;
n->location = @2;
$$ = (Node *)n;
}
| a_expr ISNULL
{
NullTest *n = makeNode(NullTest);
n->arg = (Expr *) $1;
n->nulltesttype = IS_NULL;
n->location = @2;
$$ = (Node *)n;
}
| a_expr IS NOT NULL_P %prec IS
{
NullTest *n = makeNode(NullTest);
n->arg = (Expr *) $1;
n->nulltesttype = IS_NOT_NULL;
n->location = @2;
$$ = (Node *)n;
}
| a_expr NOTNULL
{
NullTest *n = makeNode(NullTest);
n->arg = (Expr *) $1;
n->nulltesttype = IS_NOT_NULL;
n->location = @2;
$$ = (Node *)n;
}
| row OVERLAPS row
{
if (list_length($1) != 2)
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("wrong number of parameters on left side of OVERLAPS expression"),
parser_errposition(@1)));
if (list_length($3) != 2)
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("wrong number of parameters on right side of OVERLAPS expression"),
parser_errposition(@3)));
$$ = (Node *) makeFuncCall(SystemFuncName("overlaps"),
list_concat($1, $3),
@2);
}
| a_expr IS TRUE_P %prec IS
{
BooleanTest *b = makeNode(BooleanTest);
b->arg = (Expr *) $1;
b->booltesttype = IS_TRUE;
b->location = @2;
$$ = (Node *)b;
}
| a_expr IS NOT TRUE_P %prec IS
{
BooleanTest *b = makeNode(BooleanTest);
b->arg = (Expr *) $1;
b->booltesttype = IS_NOT_TRUE;
b->location = @2;
$$ = (Node *)b;
}
| a_expr IS FALSE_P %prec IS
{
BooleanTest *b = makeNode(BooleanTest);
b->arg = (Expr *) $1;
b->booltesttype = IS_FALSE;
b->location = @2;
$$ = (Node *)b;
}
| a_expr IS NOT FALSE_P %prec IS
{
BooleanTest *b = makeNode(BooleanTest);
b->arg = (Expr *) $1;
b->booltesttype = IS_NOT_FALSE;
b->location = @2;
$$ = (Node *)b;
}
| a_expr IS UNKNOWN %prec IS
{
BooleanTest *b = makeNode(BooleanTest);
b->arg = (Expr *) $1;
b->booltesttype = IS_UNKNOWN;
b->location = @2;
$$ = (Node *)b;
}
| a_expr IS NOT UNKNOWN %prec IS
{
BooleanTest *b = makeNode(BooleanTest);
b->arg = (Expr *) $1;
b->booltesttype = IS_NOT_UNKNOWN;
b->location = @2;
$$ = (Node *)b;
}
| a_expr IS DISTINCT FROM a_expr %prec IS
{
$$ = (Node *) makeSimpleA_Expr(AEXPR_DISTINCT, "=", $1, $5, @2);
}
| a_expr IS NOT DISTINCT FROM a_expr %prec IS
{
$$ = (Node *) makeSimpleA_Expr(AEXPR_NOT_DISTINCT, "=", $1, $6, @2);
}
| a_expr IS OF '(' type_list ')' %prec IS
{
$$ = (Node *) makeSimpleA_Expr(AEXPR_OF, "=", $1, (Node *) $5, @2);
}
| a_expr IS NOT OF '(' type_list ')' %prec IS
{
$$ = (Node *) makeSimpleA_Expr(AEXPR_OF, "<>", $1, (Node *) $6, @2);
}
| a_expr BETWEEN opt_asymmetric b_expr AND a_expr %prec BETWEEN
{
$$ = (Node *) makeSimpleA_Expr(AEXPR_BETWEEN,
"BETWEEN",
$1,
(Node *) list_make2($4, $6),
@2);
}
| a_expr NOT_LA BETWEEN opt_asymmetric b_expr AND a_expr %prec NOT_LA
{
$$ = (Node *) makeSimpleA_Expr(AEXPR_NOT_BETWEEN,
"NOT BETWEEN",
$1,
(Node *) list_make2($5, $7),
@2);
}
| a_expr BETWEEN SYMMETRIC b_expr AND a_expr %prec BETWEEN
{
$$ = (Node *) makeSimpleA_Expr(AEXPR_BETWEEN_SYM,
"BETWEEN SYMMETRIC",
$1,
(Node *) list_make2($4, $6),
@2);
}
| a_expr NOT_LA BETWEEN SYMMETRIC b_expr AND a_expr %prec NOT_LA
{
$$ = (Node *) makeSimpleA_Expr(AEXPR_NOT_BETWEEN_SYM,
"NOT BETWEEN SYMMETRIC",
$1,
(Node *) list_make2($5, $7),
@2);
}
| a_expr IN_P in_expr
{
/* in_expr returns a SubLink or a list of a_exprs */
if (IsA($3, SubLink))
{
/* generate foo = ANY (subquery) */
SubLink *n = (SubLink *) $3;
n->subLinkType = ANY_SUBLINK;
n->subLinkId = 0;
n->testexpr = $1;
n->operName = NIL; /* show it's IN not = ANY */
n->location = @2;
$$ = (Node *)n;
}
else
{
/* generate scalar IN expression */
$$ = (Node *) makeSimpleA_Expr(AEXPR_IN, "=", $1, $3, @2);
}
}
| a_expr NOT_LA IN_P in_expr %prec NOT_LA
{
/* in_expr returns a SubLink or a list of a_exprs */
if (IsA($4, SubLink))
{
/* generate NOT (foo = ANY (subquery)) */
/* Make an = ANY node */
SubLink *n = (SubLink *) $4;
n->subLinkType = ANY_SUBLINK;
n->subLinkId = 0;
n->testexpr = $1;
n->operName = NIL; /* show it's IN not = ANY */
n->location = @2;
/* Stick a NOT on top; must have same parse location */
$$ = makeNotExpr((Node *) n, @2);
}
else
{
/* generate scalar NOT IN expression */
$$ = (Node *) makeSimpleA_Expr(AEXPR_IN, "<>", $1, $4, @2);
}
}
| a_expr subquery_Op sub_type select_with_parens %prec Op
{
SubLink *n = makeNode(SubLink);
n->subLinkType = $3;
n->subLinkId = 0;
n->testexpr = $1;
n->operName = $2;
n->subselect = $4;
n->location = @2;
$$ = (Node *)n;
}
| a_expr subquery_Op sub_type '(' a_expr ')' %prec Op
{
if ($3 == ANY_SUBLINK)
$$ = (Node *) makeA_Expr(AEXPR_OP_ANY, $2, $1, $5, @2);
else
$$ = (Node *) makeA_Expr(AEXPR_OP_ALL, $2, $1, $5, @2);
}
| UNIQUE select_with_parens
{
/* Not sure how to get rid of the parentheses
* but there are lots of shift/reduce errors without them.
*
* Should be able to implement this by plopping the entire
* select into a node, then transforming the target expressions
* from whatever they are into count(*), and testing the
* entire result equal to one.
* But, will probably implement a separate node in the executor.
*/
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("UNIQUE predicate is not yet implemented"),
parser_errposition(@1)));
}
| a_expr IS DOCUMENT_P %prec IS
{
$$ = makeXmlExpr(IS_DOCUMENT, NULL, NIL,
list_make1($1), @2);
}
| a_expr IS NOT DOCUMENT_P %prec IS
{
$$ = makeNotExpr(makeXmlExpr(IS_DOCUMENT, NULL, NIL,
list_make1($1), @2),
@2);
}
| DEFAULT
{
/*
* The SQL spec only allows DEFAULT in "contextually typed
* expressions", but for us, it's easier to allow it in
* any a_expr and then throw error during parse analysis
* if it's in an inappropriate context. This way also
* lets us say something smarter than "syntax error".
*/
SetToDefault *n = makeNode(SetToDefault);
/* parse analysis will fill in the rest */
n->location = @1;
$$ = (Node *)n;
}
;
二、语义解析
src\backend\parser\analyze.c中做了语义解析。在exec_simple_query函数中获取词法解析树（pg_parse_query），对解析树进行优化重新（pg_analyze_and_rewrite），对解析树指定执行计划（pg_plan_queries），执行命令（PortalStart）。
该文件中主要介绍怎么获取词法解析树。
1、pg_parse_query词法解析树获取
/*
* Do raw parsing (only).
*
* A list of parsetrees (RawStmt nodes) is returned, since there might be
* multiple commands in the given string.
*
* NOTE: for interactive queries, it is important to keep this routine
* separate from the analysis & rewrite stages. Analysis and rewriting
* cannot be done in an aborted transaction, since they require access to
* database tables. So, we rely on the raw parser to determine whether
* we've seen a COMMIT or ABORT command; when we are in abort state, other
* commands are not processed any further than the raw parse stage.
*/
//将完整的语句传入该函数
List *
pg_parse_query(const char *query_string)
{
List *raw_parsetree_list;
TRACE_POSTGRESQL_QUERY_PARSE_START(query_string);
if (log_parser_stats)
ResetUsage();
//调用词法解析器解析语句
raw_parsetree_list = raw_parser(query_string);
if (log_parser_stats)
ShowUsage("PARSER STATISTICS");
#ifdef COPY_PARSE_PLAN_TREES
/* Optional debugging check: pass raw parsetrees through copyObject() */
{
List *new_list = copyObject(raw_parsetree_list);
/* This checks both copyObject() and the equal() routines... */
if (!equal(new_list, raw_parsetree_list))
elog(WARNING, "copyObject() failed to produce an equal raw parse tree");
else
raw_parsetree_list = new_list;
}
#endif
/*
* Currently, outfuncs/readfuncs support is missing for many raw parse
* tree nodes, so we don't try to implement WRITE_READ_PARSE_PLAN_TREES
* here.
*/
TRACE_POSTGRESQL_QUERY_PARSE_DONE(query_string);
return raw_parsetree_list;
}
/*
* raw_parser
* Given a query in string form, do lexical and grammatical analysis.
*
* Returns a list of raw (un-analyzed) parse trees. The immediate elements
* of the list are always RawStmt nodes.
*/
List *
raw_parser(const char *str)
{
core_yyscan_t yyscanner;
base_yy_extra_type yyextra;
int yyresult;
//初始化flex
/* initialize the flex scanner */
yyscanner = scanner_init(str, &yyextra.core_yy_extra,
&ScanKeywords, ScanKeywordTokens);
/* base_yylex() only needs this much initialization */
yyextra.have_lookahead = false;
//初始化bison
/* initialize the bison parser */
parser_init(&yyextra);
//执行解析
/* Parse! */
yyresult = base_yyparse(yyscanner);
/* Clean up (release memory) */
scanner_finish(yyscanner);
if (yyresult) /* error */
return NIL;
return yyextra.parsetree;
}
最终base_yyparse函数被调用，返回yyextra.parsetree变量。该变量在gram.y中被赋值。完成解析。
/*
* The target production for the whole parse.
*/
stmtblock: stmtmulti
{
pg_yyget_extra(yyscanner)->parsetree = $1;
}
;
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