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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