本節繼續介紹PostgreSQL的語法分析定義檔案gram.y的第二部分Definitions.
Bison輸入檔案的組成:
```
%{
Declarations
%}
Definitions
%%
Productions
%%
User subroutines
```

### 一、Definitions
Definitions在Bison的作用與Flex中的功能也差不多,在這個段定義一些Bison專有變數或相關選項.
**%purge-parser**
指示Bison建立一個可重入的解析器.與普通的解析器一個很大的不同的,yylval的型別是union指標而不是union.

**%expect**
%expect N告訴Bison，解析器應該有N個shift/reduce衝突，如果不匹配，Bison將報告編譯時錯誤。

**%name-prefix**
命名函式名稱,預設為yy
%name-prefix "base_yy"意味著預設的yyxx()會變成base_yyxx().比如yyparse(),yylex(),yyerror(),yylval,yychar和
yydebug.

**%locations**
位置

**%parse-param**
%parse-param宣告的內容位於yyparse()的括號之間,可以宣告任意多的引數.
比如%parse-param {core_yyscan_t yyscanner},引數為core_yyscan_t yyscanner.

**%lex-param**
%lex-param宣告的內容位於yylex()的括號之間,可以宣告任意多的引數.
比如%lex-param {core_yyscan_t yyscanner},引數為core_yyscan_t yyscanner.

**%union**
%union宣告瞭在解析器中識別符號所使用的型別.
Bison解析器,每一個識別符號,包括tokens和非終結符,都有值與之關聯,預設的,值的型別都是整型,但在實際應用中遠遠不夠.
%union可以為識別符號值建立C語言union宣告.
```
%union
{
	core_YYSTYPE		core_yystype;
	/* these fields must match core_YYSTYPE: */
	int					ival;
	char				*str;
	const char			*keyword;
	...
}

```
其中core_yystype的型別為core_YYSTYPE聯合體.
```
/*
 * 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;

```
一旦定義了union,那需要透過將union中合適的名稱放在尖括號(<>)中,用以告訴Bison哪些符號具有哪些型別的值.

**%type**
型別定義,如:
```
%type <node>	stmt schema_stmt
		AlterEventTrigStmt AlterCollationStmt
		...
```
表示識別符號/非終結符<node>的型別可以是stmt/schema_stmt/AlterEventTrigStmt/...

**%nonassoc**
使用%nonassoc宣告非關聯運算子。

**%left**
左關聯運算子

**%right**
右關聯運算子

### 二、gram.y定義部分原始碼
```

%pure-parser
%expect 0
%name-prefix="base_yy"
%locations

%parse-param {core_yyscan_t yyscanner}
%lex-param   {core_yyscan_t yyscanner}

%union
{
	core_YYSTYPE		core_yystype;
	/* these fields must match core_YYSTYPE: */
	int					ival;
	char				*str;
	const char			*keyword;

char				chr;
	bool				boolean;
	JoinType			jtype;
	DropBehavior		dbehavior;
	OnCommitAction		oncommit;
	List				*list;
	Node				*node;
	Value				*value;
	ObjectType			objtype;
	TypeName			*typnam;
	FunctionParameter   *fun_param;
	FunctionParameterMode fun_param_mode;
	ObjectWithArgs		*objwithargs;
	DefElem				*defelt;
	SortBy				*sortby;
	WindowDef			*windef;
	JoinExpr			*jexpr;
	IndexElem			*ielem;
	Alias				*alias;
	RangeVar			*range;
	IntoClause			*into;
	WithClause			*with;
	InferClause			*infer;
	OnConflictClause	*onconflict;
	A_Indices			*aind;
	ResTarget			*target;
	struct PrivTarget	*privtarget;
	AccessPriv			*accesspriv;
	struct ImportQual	*importqual;
	InsertStmt			*istmt;
	VariableSetStmt		*vsetstmt;
	PartitionElem		*partelem;
	PartitionSpec		*partspec;
	PartitionBoundSpec	*partboundspec;
	RoleSpec			*rolespec;
}

%type <node>	stmt schema_stmt
		AlterEventTrigStmt AlterCollationStmt
		AlterDatabaseStmt AlterDatabaseSetStmt AlterDomainStmt AlterEnumStmt
		AlterFdwStmt AlterForeignServerStmt AlterGroupStmt
		AlterObjectDependsStmt AlterObjectSchemaStmt AlterOwnerStmt
		AlterOperatorStmt AlterSeqStmt AlterSystemStmt AlterTableStmt
		AlterTblSpcStmt AlterExtensionStmt AlterExtensionContentsStmt AlterForeignTableStmt
		AlterCompositeTypeStmt AlterUserMappingStmt
		AlterRoleStmt AlterRoleSetStmt AlterPolicyStmt
		AlterDefaultPrivilegesStmt DefACLAction
		AnalyzeStmt CallStmt ClosePortalStmt ClusterStmt CommentStmt
		ConstraintsSetStmt CopyStmt CreateAsStmt CreateCastStmt
		CreateDomainStmt CreateExtensionStmt CreateGroupStmt CreateOpClassStmt
		CreateOpFamiXXXtmt AlterOpFamiXXXtmt CreatePLangStmt
		CreateSchemaStmt CreateSeqStmt CreateStmt CreateStatsStmt CreateTableSpaceStmt
		CreateFdwStmt CreateForeignServerStmt CreateForeignTableStmt
		CreateAssertStmt CreateTransformStmt CreateTrigStmt CreateEventTrigStmt
		CreateUserStmt CreateUserMappingStmt CreateRoleStmt CreatePolicyStmt
		CreatedbStmt DeclareCursorStmt DefineStmt DeleteStmt DiscardStmt DoStmt
		DropOpClassStmt DropOpFamiXXXtmt DropPLangStmt DropStmt
		DropAssertStmt DropCastStmt DropRoleStmt
		DropdbStmt DropTableSpaceStmt
		DropTransformStmt
		DropUserMappingStmt ExplainStmt FetchStmt
		GrantStmt GrantRoleStmt ImportForeignSchemaStmt IndexStmt InsertStmt
		ListenStmt LoadStmt LockStmt NotifyStmt ExplainableStmt PreparableStmt
		CreateFunctionStmt AlterFunctionStmt ReindexStmt RemoveAggrStmt
		RemoveFuncStmt RemoveOperStmt RenameStmt RevokeStmt RevokeRoleStmt
		RuleActionStmt RuleActionStmtOrEmpty RuleStmt
		SecLabelStmt SelectStmt TransactionStmt TruncateStmt
		UnlistenStmt UpdateStmt VacuumStmt
		VariableResetStmt VariableSetStmt VariableShowStmt
		ViewStmt CheckPointStmt CreateConversionStmt
		DeallocateStmt PrepareStmt ExecuteStmt
		DropOwnedStmt ReassignOwnedStmt
		AlterTSConfigurationStmt AlterTSDictionaryStmt
		CreateMatViewStmt RefreshMatViewStmt CreateAmStmt
		CreatePublicationStmt AlterPublicationStmt
		CreateSubscriptionStmt AlterSubscriptionStmt DropSubscriptionStmt

%type <node>	select_no_parens select_with_parens select_clause
				simple_select values_clause

%type <node>	alter_column_default opclass_item opclass_drop alter_using
%type <ival>	add_drop opt_asc_desc opt_nulls_order

%type <node>	alter_table_cmd alter_type_cmd opt_collate_clause
	   replica_identity partition_cmd index_partition_cmd
%type <list>	alter_table_cmds alter_type_cmds
%type <list>    alter_identity_column_option_list
%type <defelt>  alter_identity_column_option

%type <dbehavior>	opt_drop_behavior

%type <list>	createdb_opt_list createdb_opt_items copy_opt_list
				transaction_mode_list
				create_extension_opt_list alter_extension_opt_list
%type <defelt>	createdb_opt_item copy_opt_item
				transaction_mode_item
				create_extension_opt_item alter_extension_opt_item

%type <ival>	opt_lock lock_type cast_context
%type <ival>	vacuum_option_list vacuum_option_elem
				analyze_option_list analyze_option_elem
%type <boolean>	opt_or_replace
				opt_grant_grant_option opt_grant_admin_option
				opt_nowait opt_if_exists opt_with_data
%type <ival>	opt_nowait_or_skip

%type <list>	OptRoleList AlterOptRoleList
%type <defelt>	CreateOptRoleElem AlterOptRoleElem

%type <str>		opt_type
%type <str>		foreign_server_version opt_foreign_server_version
%type <str>		opt_in_database

%type <str>		OptSchemaName
%type <list>	OptSchemaEltList

%type <boolean> TriggerForSpec TriggerForType
%type <ival>	TriggerActionTime
%type <list>	TriggerEvents TriggerOneEvent
%type <value>	TriggerFuncArg
%type <node>	TriggerWhen
%type <str>		TransitionRelName
%type <boolean>	TransitionRowOrTable TransitionOldOrNew
%type <node>	TriggerTransition

%type <list>	event_trigger_when_list event_trigger_value_list
%type <defelt>	event_trigger_when_item
%type <chr>		enable_trigger

%type <str>		copy_file_name
				database_name access_method_clause access_method attr_name
				name cursor_name file_name
				index_name opt_index_name cluster_index_specification

%type <list>	func_name handler_name qual_Op qual_all_Op subquery_Op
				opt_class opt_inline_handler opt_validator validator_clause
				opt_collate

%type <range>	qualified_name insert_target OptConstrFromTable

%type <str>		all_Op MathOp

%type <str>		row_security_cmd RowSecurityDefaultForCmd
%type <boolean> RowSecurityDefaultPermissive
%type <node>	RowSecurityOptionalWithCheck RowSecurityOptionalExpr
%type <list>	RowSecurityDefaultToRole RowSecurityOptionalToRole

%type <str>		iso_level opt_encoding
%type <rolespec> grantee
%type <list>	grantee_list
%type <accesspriv> privilege
%type <list>	privileges privilege_list
%type <privtarget> privilege_target
%type <objwithargs> function_with_argtypes aggregate_with_argtypes operator_with_argtypes
%type <list>	function_with_argtypes_list aggregate_with_argtypes_list operator_with_argtypes_list
%type <ival>	defacl_privilege_target
%type <defelt>	DefACLOption
%type <list>	DefACLOptionList
%type <ival>	import_qualification_type
%type <importqual> import_qualification
%type <node>	vacuum_relation

%type <list>	stmtblock stmtmulti
				OptTableElementList TableElementList OptInherit definition
				OptTypedTableElementList TypedTableElementList
				reloptions opt_reloptions
				OptWith distinct_clause opt_all_clause opt_definition func_args func_args_list
				func_args_with_defaults func_args_with_defaults_list
				aggr_args aggr_args_list
				func_as createfunc_opt_list alterfunc_opt_list
				old_aggr_definition old_aggr_list
				oper_argtypes RuleActionList RuleActionMulti
				opt_column_list columnList opt_name_list
				sort_clause opt_sort_clause sortby_list index_params
				opt_include opt_c_include index_including_params
				name_list role_list from_clause from_list opt_array_bounds
				qualified_name_list any_name any_name_list type_name_list
				any_operator expr_list attrs
				target_list opt_target_list insert_column_list set_target_list
				set_clause_list set_clause
				def_list operator_def_list indirection opt_indirection
				reloption_list group_clause TriggerFuncArgs select_limit
				opt_select_limit opclass_item_list opclass_drop_list
				opclass_purpose opt_opfamily transaction_mode_list_or_empty
				OptTableFuncElementList TableFuncElementList opt_type_modifiers
				prep_type_clause
				execute_param_clause using_clause returning_clause
				opt_enum_val_list enum_val_list table_func_column_list
				create_generic_options alter_generic_options
				relation_expr_list dostmt_opt_list
				transform_element_list transform_type_list
				TriggerTransitions TriggerReferencing
				publication_name_list
				vacuum_relation_list opt_vacuum_relation_list

%type <list>	group_by_list
%type <node>	group_by_item empty_grouping_set rollup_clause cube_clause
%type <node>	grouping_sets_clause
%type <node>	opt_publication_for_tables publication_for_tables
%type <value>	publication_name_item

%type <list>	opt_fdw_options fdw_options
%type <defelt>	fdw_option

%type <range>	OptTempTableName
%type <into>	into_clause create_as_target create_mv_target

%type <defelt>	createfunc_opt_item common_func_opt_item dostmt_opt_item
%type <fun_param> func_arg func_arg_with_default table_func_column aggr_arg
%type <fun_param_mode> arg_class
%type <typnam>	func_return func_type

%type <boolean>  opt_trusted opt_restart_seqs
%type <ival>	 OptTemp
%type <ival>	 OptNoLog
%type <oncommit> OnCommitOption

%type <ival>	for_locking_strength
%type <node>	for_locking_item
%type <list>	for_locking_clause opt_for_locking_clause for_locking_items
%type <list>	locked_rels_list
%type <boolean>	all_or_distinct

%type <node>	join_outer join_qual
%type <jtype>	join_type

%type <list>	extract_list overlay_list position_list
%type <list>	substr_list trim_list
%type <list>	opt_interval interval_second
%type <node>	overlay_placing substr_from substr_for

%type <boolean> opt_instead
%type <boolean> opt_unique opt_concurrently opt_verbose opt_full
%type <boolean> opt_freeze opt_analyze opt_default opt_recheck
%type <defelt>	opt_binary opt_oids copy_delimiter

%type <boolean> copy_from opt_program

%type <ival>	opt_column event cursor_options opt_hold opt_set_data
%type <objtype>	drop_type_any_name drop_type_name drop_type_name_on_any_name
				comment_type_any_name comment_type_name
				security_label_type_any_name security_label_type_name

%type <node>	fetch_args limit_clause select_limit_value
				offset_clause select_offset_value
				select_fetch_first_value I_or_F_const
%type <ival>	row_or_rows first_or_next

%type <list>	OptSeqOptList SeqOptList OptParenthesizedSeqOptList
%type <defelt>	SeqOptElem

%type <istmt>	insert_rest
%type <infer>	opt_conf_expr
%type <onconflict> opt_on_conflict

%type <vsetstmt> generic_set set_rest set_rest_more generic_reset reset_rest
				 SetResetClause FunctionSetResetClause

%type <node>	TableElement TypedTableElement ConstraintElem TableFuncElement
%type <node>	columnDef columnOptions
%type <defelt>	def_elem reloption_elem old_aggr_elem operator_def_elem
%type <node>	def_arg columnElem where_clause where_or_current_clause
				a_expr b_expr c_expr AexprConst indirection_el opt_slice_bound
				columnref in_expr having_clause func_table xmltable array_expr
				ExclusionWhereClause operator_def_arg
%type <list>	rowsfrom_item rowsfrom_list opt_col_def_list
%type <boolean> opt_ordinality
%type <list>	ExclusionConstraintList ExclusionConstraintElem
%type <list>	func_arg_list
%type <node>	func_arg_expr
%type <list>	row explicit_row implicit_row type_list array_expr_list
%type <node>	case_expr case_arg when_clause case_default
%type <list>	when_clause_list
%type <ival>	sub_type
%type <value>	NumericOnly
%type <list>	NumericOnly_list
%type <alias>	alias_clause opt_alias_clause
%type <list>	func_alias_clause
%type <sortby>	sortby
%type <ielem>	index_elem
%type <node>	table_ref
%type <jexpr>	joined_table
%type <range>	relation_expr
%type <range>	relation_expr_opt_alias
%type <node>	tablesample_clause opt_repeatable_clause
%type <target>	target_el set_target insert_column_item

%type <str>		generic_option_name
%type <node>	generic_option_arg
%type <defelt>	generic_option_elem alter_generic_option_elem
%type <list>	generic_option_list alter_generic_option_list
%type <str>		explain_option_name
%type <node>	explain_option_arg
%type <defelt>	explain_option_elem
%type <list>	explain_option_list

%type <ival>	reindex_target_type reindex_target_multitable
%type <ival>	reindex_option_list reindex_option_elem

%type <node>	copy_generic_opt_arg copy_generic_opt_arg_list_item
%type <defelt>	copy_generic_opt_elem
%type <list>	copy_generic_opt_list copy_generic_opt_arg_list
%type <list>	copy_options

%type <typnam>	Typename SimpleTypename ConstTypename
				GenericType Numeric opt_float
				Character ConstCharacter
				CharacterWithLength CharacterWithoutLength
				ConstDatetime ConstInterval
				Bit ConstBit BitWithLength BitWithoutLength
%type <str>		character
%type <str>		extract_arg
%type <boolean> opt_varying opt_timezone opt_no_inherit

%type <ival>	Iconst SignedIconst
%type <str>		Sconst comment_text notify_payload
%type <str>		RoleId opt_boolean_or_string
%type <list>	var_list
%type <str>		ColId ColLabel var_name type_function_name param_name
%type <str>		NonReservedWord NonReservedWord_or_Sconst
%type <str>		createdb_opt_name
%type <node>	var_value zone_value
%type <rolespec> auth_ident RoleSpec opt_granted_by

%type <keyword> unreserved_keyword type_func_name_keyword
%type <keyword> col_name_keyword reserved_keyword

%type <node>	TableConstraint TableLikeClause
%type <ival>	TableLikeOptionList TableLikeOption
%type <list>	ColQualList
%type <node>	ColConstraint ColConstraintElem ConstraintAttr
%type <ival>	key_actions key_delete key_match key_update key_action
%type <ival>	ConstraintAttributeSpec ConstraintAttributeElem
%type <str>		ExistingIndex

%type <list>	constraints_set_list
%type <boolean> constraints_set_mode
%type <str>		OptTableSpace OptConsTableSpace
%type <rolespec> OptTableSpaceOwner
%type <ival>	opt_check_option

%type <str>		opt_provider security_label

%type <target>	xml_attribute_el
%type <list>	xml_attribute_list xml_attributes
%type <node>	xml_root_version opt_xml_root_standalone
%type <node>	xmlexists_argument
%type <ival>	document_or_content
%type <boolean> xml_whitespace_option
%type <list>	xmltable_column_list xmltable_column_option_list
%type <node>	xmltable_column_el
%type <defelt>	xmltable_column_option_el
%type <list>	xml_namespace_list
%type <target>	xml_namespace_el

%type <node>	func_application func_expr_common_subexpr
%type <node>	func_expr func_expr_windowless
%type <node>	common_table_expr
%type <with>	with_clause opt_with_clause
%type <list>	cte_list

%type <list>	within_group_clause
%type <node>	filter_clause
%type <list>	window_clause window_definition_list opt_partition_clause
%type <windef>	window_definition over_clause window_specification
				opt_frame_clause frame_extent frame_bound
%type <ival>	opt_window_exclusion_clause
%type <str>		opt_existing_window_name
%type <boolean> opt_if_not_exists
%type <ival>	generated_when override_kind
%type <partspec>	PartitionSpec OptPartitionSpec
%type <str>			part_strategy
%type <partelem>	part_elem
%type <list>		part_params
%type <partboundspec> PartitionBoundSpec
%type <node>		partbound_datum PartitionRangeDatum
%type <list>		hash_partbound partbound_datum_list range_datum_list
%type <defelt>		hash_partbound_elem

/*
 * Non-keyword token types.  These are hard-wired into the "flex" lexer.
 * They must be listed first so that their numeric codes do not depend on
 * the set of keywords.  PL/pgSQL depends on this so that it can share the
 * same lexer.  If you add/change tokens here, fix PL/pgSQL to match!
 * 非關鍵字token型別.
 * 這些都被硬連結到"flex"的詞法分析器中.
 * 必須首先列出這些token,這樣他們的數字程式碼就不用依賴關鍵字集合了.
 * PL/pgsQL依賴於該集合以便可以共享相同的詞法分析器.
 * 如果在這裡新增/修改tokens,那麼注意相應的修改PL/pgSQL.
 *
 * DOT_DOT is unused in the core SQL grammar, and so will always provoke
 * parse errors.  It is needed by PL/pgSQL.
 * DOT_DOT在核心SQL語法中不會使用,因此通常會提示解析錯誤.用於PL/pgSQL.
 */
%token <str>	IDENT FCONST SCONST BCONST XCONST Op
%token <ival>	ICONST PARAM
%token			TYPECAST DOT_DOT COLON_EQUALS EQUALS_GREATER
%token			LESS_EQUALS GREATER_EQUALS NOT_EQUALS

/*
 * If you want to make any keyword changes, update the keyword table in
 * src/include/parser/kwlist.h and add new keywords to the appropriate one
 * of the reserved-or-not-so-reserved keyword lists, below; search
 * this file for "Keyword category lists".
 * 如果希望修改關鍵字,更新src/include/parser/kwlist.h,
 *   同時在下面的關鍵字列表中在合適的位置新增新的關鍵字.可在檔案中搜尋"Keyword category lists"
 */

/* ordinary key words in alphabetical order */
//以字母順序排列的普通關鍵字.
%token <keyword> ABORT_P ABSOLUTE_P ACCESS ACTION ADD_P ADMIN AFTER
	AGGREGATE ALL ALSO ALTER ALWAYS ANAXXXE ANALYZE AND ANY ARRAY AS ASC
	ASSERTION ASSIGNMENT ASYMMETRIC AT ATTACH ATTRIBUTE AUTHORIZATION

BACKWARD BEFORE BEGIN_P BETWEEN BIGINT BINARY BIT
	BOOLEAN_P BOTH BY

CACHE CALL CALLED CASCADE CASCADED CASE CAST CATALOG_P CHAIN CHAR_P
	CHARACTER CHARACTERISTICS CHECK CHECKPOINT CLASS CLOSE
	CLUSTER COALESCE COLLATE COLLATION COLUMN COLUMNS COMMENT COMMENTS COMMIT
	COMMITTED CONCURRENTLY CONFIGURATION CONFLICT CONNECTION CONSTRAINT
	CONSTRAINTS CONTENT_P CONTINUE_P CONVERSION_P COPY COST CREATE
	CROSS CSV CUBE CURRENT_P
	CURRENT_CATALOG CURRENT_DATE CURRENT_ROLE CURRENT_SCHEMA
	CURRENT_TIME CURRENT_TIMESTAMP CURRENT_USER CURSOR CYCLE

DATA_P DATABASE DAY_P DEALLOCATE DEC DECIMAL_P DECLARE DEFAULT DEFAULTS
	DEFERRABLE DEFERRED DEFINER DELETE_P DELIMITER DELIMITERS DEPENDS DESC
	DETACH DICTIONARY DISABLE_P DISCARD DISTINCT DO DOCUMENT_P DOMAIN_P
	DOUBLE_P DROP

EACH ELSE ENABLE_P ENCODING ENCRYPTED END_P ENUM_P ESCAPE EVENT EXCEPT
	EXCLUDE EXCLUDING EXCLUSIVE EXECUTE EXISTS EXPLAIN
	EXTENSION EXTERNAL EXTRACT

FALSE_P FAMILY FETCH FILTER FIRST_P FLOAT_P FOLLOWING FOR
	FORCE FOREIGN FORWARD FREEZE FROM FULL FUNCTION FUNCTIONS

GENERATED GLOBAL GRANT GRANTED GREATEST GROUP_P GROUPING GROUPS

HANDLER HAVING HEADER_P HOLD HOUR_P

IDENTITY_P IF_P ILIKE IMMEDIATE IMMUTABLE IMPLICIT_P IMPORT_P IN_P INCLUDE
	INCLUDING INCREMENT INDEX INDEXES INHERIT INHERITS INITIALLY INLINE_P
	INNER_P INOUT INPUT_P INSENSITIVE INSERT INSTEAD INT_P INTEGER
	INTERSECT INTERVAL INTO INVOKER IS ISNULL ISOLATION

JOIN

KEY

LABEL LANGUAGE LARGE_P LAST_P LATERAL_P
	LEADING LEAKPROOF LEAST LEFT LEVEL LIKE LIMIT LISTEN LOAD LOCAL
	LOCALTIME LOCALTIMESTAMP LOCATION LOCK_P LOCKED LOGGED

MAPPING MATCH MATERIALIZED MAXVALUE METHOD MINUTE_P MINVALUE MODE MONTH_P MOVE

NAME_P NAMES NATIONAL NATURAL NCHAR NEW NEXT NO NONE
	NOT NOTHING NOTIFY NOTNULL NOWAIT NULL_P NULLIF
	NULLS_P NUMERIC

OBJECT_P OF OFF OFFSET OIDS OLD ON ONLY OPERATOR OPTION OPTIONS OR
	ORDER ORDINALITY OTHERS OUT_P OUTER_P
	OVER OVERLAPS OVERLAY OVERRIDING OWNED OWNER

PARALLEL PARSER PARTIAL PARTITION PASSING PASSWORD PLACING PLANS POLICY
	POSITION PRECEDING PRECISION PRESERVE PREPARE PREPARED PRIMARY
	PRIOR PRIVILEGES PROCEDURAL PROCEDURE PROCEDURES PROGRAM PUBLICATION

QUOTE

RANGE READ REAL REASSIGN RECHECK RECURSIVE REF REFERENCES REFERENCING
	REFRESH REINDEX RELATIVE_P RELEASE RENAME REPEATABLE REPLACE REPLICA
	RESET RESTART RESTRICT RETURNING RETURNS REVOKE RIGHT ROLE ROLLBACK ROLLUP
	ROUTINE ROUTINES ROW ROWS RULE

SAVEPOINT SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT SEQUENCE SEQUENCES
	SERIALIZABLE SERVER SESSION SESSION_USER SET SETS SETOF SHARE SHOW
	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SQL_P STABLE STANDALONE_P
	START STATEMENT STATISTICS STDIN STDOUT STORAGE STRICT_P STRIP_P
	SUBSCRIPTION SUBSTRING SYMMETRIC SYSID SYSTEM_P

TABLE TABLES TABLESAMPLE TABLESPACE TEMP TEMPLATE TEMPORARY TEXT_P THEN
	TIES TIME TIMESTAMP TO TRAILING TRANSACTION TRANSFORM
	TREAT TRIGGER TRIM TRUE_P
	TRUNCATE TRUSTED TYPE_P TYPES_P

UNBOUNDED UNCOMMITTED UNENCRYPTED UNION UNIQUE UNKNOWN UNLISTEN UNLOGGED
	UNTIL UPDATE USER USING

VACUUM VALID VALIDATE VALIDATOR VALUE_P VALUES VARCHAR VARIADIC VARYING
	VERBOSE VERSION_P VIEW VIEWS VOLATILE

WHEN WHERE WHITESPACE_P WINDOW WITH WITHIN WITHOUT WORK WRAPPER WRITE

XML_P XMLATTRIBUTES XMLCONCAT XMLELEMENT XMLEXISTS XMLFOREST XMLNAMESPACES
	XMLPARSE XMLPI XMLROOT XMLSERIALIZE XMLTABLE

YEAR_P YES_P

ZONE

/*
 * The grammar thinks these are keywords, but they are not in the kwlist.h
 * list and so can never be entered directly.  The filter in parser.c
 * creates these tokens when required (based on looking one token ahead).
 * 語法分析器認為存在關鍵字,但這些關鍵字沒有在kwlist.h中列出,因此永遠都不能直接進入.
 * parser.c中的過濾器在需要的時候建立這些tokens(基於提前檢視一個token).
 *
 * NOT_LA exists so that productions such as NOT LIKE can be given the same
 * precedence as LIKE; otherwise they'd effectively have the same precedence
 * as NOT, at least with respect to their left-hand subexpression.
 * NULLS_LA and WITH_LA are needed to make the grammar LALR(1).
 * NOT_LA之所以存在以便諸如NOT LIKE這樣的產生式可與LIKE具備同樣的優先順序.
 * 否則它們會與NOT的優先順序一樣,至少對於他們的左子表示式如此.
 * NULLS_LA和WITH_LA用於產生LALR(1)語法解析器.
 */
%token		NOT_LA NULLS_LA WITH_LA

/* Precedence: lowest to highest */
//優先順序:從低到高
%nonassoc	SET				/* see relation_expr_opt_alias */
%left		UNION EXCEPT
%left		INTERSECT
%left		OR
%left		AND
%right		NOT
%nonassoc	IS ISNULL NOTNULL	/* IS sets precedence for IS NULL, etc */
%nonassoc	'' '=' LESS_EQUALS GREATER_EQUALS NOT_EQUALS
%nonassoc	BETWEEN IN_P LIKE ILIKE SIMILAR NOT_LA
//轉義操作
%nonassoc	ESCAPE			/* ESCAPE must be just above LIKE/ILIKE/SIMILAR */
%left		POSTFIXOP		/* dummy for postfix Op rules */

/*
 * To support target_el without AS, we must give IDENT an explicit priority
 * between POSTFIXOP and Op.  We can safely assign the same priority to
 * various unreserved keywords as needed to resolve ambiguities (this can't
 * have any bad effects since obviously the keywords will still behave the
 * same as if they weren't keywords).  We need to do this:
 * for PARTITION, RANGE, ROWS, GROUPS to support opt_existing_window_name;
 * for RANGE, ROWS, GROUPS so that they can follow a_expr without creating
 * postfix-operator problems;
 * for GENERATED so that it can follow b_expr;
 * and for NULL so that it can follow b_expr in ColQualList without creating
 * postfix-operator problems.
 * 為了支援沒有AS的target_el,必須在POSTFIXOP和Op之間明確的給IDENT一個顯式的優先順序.
 * 我們可以根據需要安全地為各種未保留的關鍵字分配相同的優先順序,以解決歧義.
 * (這不會有什麼不好的影響,因為顯然的,關鍵字的行為與它們不是關鍵字是一樣的).
 * 我們需要做的事情是:
 *   對於PARTITION, RANGE, ROWS, GROUPS,需要支援opt_existing_window_name;
 *   對於RANGE, ROWS, GROUPS,以便它們可以跟隨a_expr而不會產生字尾運算子問題;
 *   對於GENERATED,可以跟隨b_expr;
 *   對於NULL,可以在ColQualList中跟隨b_expr而不會產生字尾運算子問題;
 *
 * To support CUBE and ROLLUP in GROUP BY without reserving them, we give them
 * an explicit priority lower than '(', so that a rule with CUBE '(' will shift
 * rather than reducing a conflicting rule that takes CUBE as a function name.
 * Using the same precedence as IDENT seems right for the reasons given above.
 * 在GROUP BY中支援CUBE/ROLLUP而無需保留它們,我們給予它們顯示的優先順序,要低於字元'(',
 *   這樣存在CUBE '('的規則會進行狀態轉換而不是把CUBE視為函式名稱而產生摺疊衝突的規則.
 * 基於以上的理由,使用與IDENT相同的優先順序似乎是正確的.
 *
 * The frame_bound productions UNBOUNDED PRECEDING and UNBOUNDED FOLLOWING
 * are even messier: since UNBOUNDED is an unreserved keyword (per spec!),
 * there is no principled way to distinguish these from the productions
 * .  We hack this up by giving UNBOUNDED slightly
 * lower precedence than PRECEDING and FOLLOWING.  At present this doesn't
 * appear to cause UNBOUNDED to be treated differently from other unreserved
 * keywords anywhere else in the grammar, but it's definitely risky.  We can
 * blame any funny behavior of UNBOUNDED on the SQL standard, though.
 * frame_bound產生式UNBOUNDED PRECEDING和UNBOUNDED FOLLOWING更加混亂:
 * 因為UNBOUNDED是非保留關鍵字(per spec!),不存在明確的原則來區分產生式.
 * 透過給UNBOUNDED的優先順序比PRECEDING和FOLLOWING更低優先順序來解決此問題.
 * 到現在為止,看起來不會產生把UNBOUNDED與語法中其他任何地方的非保留關鍵字區別對待,
 *   但這肯定存在風險.
 * 不過,我們可以將UNBOUNDED的任何有趣行為歸咎於SQL標準。
 *
 */
//理想的情況下不應存在於IDENT相同的優先順序.
%nonassoc	UNBOUNDED		/* ideally should have same precedence as IDENT */
%nonassoc	IDENT GENERATED NULL_P PARTITION RANGE ROWS GROUPS PRECEDING FOLLOWING CUBE ROLLUP
//多字元組成的運算子和使用者自定義運算子
%left		Op OPERATOR		/* multi-character ops and user-defined operators */
%left		'+' '-'
%left		'*' '/' '%'
%left		'^'
/* Unary Operators */
//一元運算子
%left		AT				/* sets precedence for AT TIME ZONE */
%left		COLLATE
%right		UMINUS
%left		'[' ']'
%left		'(' ')'
%left		TYPECAST
%left		'.'
/*
 * These might seem to be low-precedence, but actually they are not part
 * of the arithmetic hierarchy at all in their use as JOIN operators.
 * We make them high-precedence to support their use as function names.
 * They wouldn't be given a precedence at all, were it not that we need
 * left-associativity among the JOIN rules themselves.
 * 這些運算子看起來優先順序比較低,但實際上在把它們作為連線運算子時,
 *   它們根本不是算術層次結構的一部分.
 * 提高它們的優先順序,可以支援將它們用作函式名稱.
 * 如果我們不需要連線規則本身的左結合性,它們根本就不會被授予優先順序.
 */
%left		JOIN CROSS LEFT FULL RIGHT INNER_P NATURAL
/* kluge to keep xml_whitespace_option from causing shift/reduce conflicts */
//可防止xml_whitespace_option引起的轉移/摺疊衝突.
%right		PRESERVE STRIP_P

```

### 三、參考資料
[Flex&Bison](http://web.iitd.ac.in/~sumeet/flex__bison.pdf)</keyword></ival></str></defelt></list></node></partboundspec></list></partelem></str></partspec></ival></boolean></str></ival></windef></list></node></list></list></with></node></node></node></target></list></defelt></node></list></boolean></ival></node></node></list></target></str></ival></rolespec></str></boolean></list></str></ival></ival></node></list></ival></node></keyword></keyword></rolespec></node></str></str></str></list></str></str></ival></boolean></str></str></typnam></list></list></defelt></node></ival></ival></list></defelt></node></str></list></defelt></node></str></target></node></range></range></jexpr></node></ielem></sortby></list></alias></list></value></ival></list></node></list></node></list></list></boolean></list></node></defelt></node></node></vsetstmt></onconflict></infer></istmt></defelt></list></ival></node></objtype></ival></boolean></defelt></boolean></boolean></boolean></node></list></list></list></jtype></node></boolean></list></list></node></ival></oncommit></ival></ival></boolean></typnam></fun_param_mode></fun_param></defelt></into></range></defelt></list></value></node></node></node></list></list></node></importqual></ival></list></defelt></ival></list></objwithargs></privtarget></list></accesspriv></list></rolespec></str></list></node></boolean></str></str></range></list></str></chr></defelt></list></node></boolean></str></node></value></list></ival></boolean></list></str></str></str></str></defelt></list></ival></boolean></ival></ival></defelt></list></dbehavior></defelt></list></list></node></ival></node></node></node></node></node>

PostgreSQL 原始碼解讀（175）- 查詢#93(語法分析：gram.y)#2

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