PostgreSQL源码解读（175）-查询#93(语法分析：gram.y)#2

本节继续介绍PostgreSQL的语法分析定义文件gram.y的第二部分Definitions.
Bison输入文件的组成:

%{
Declarations
%}
Definitions
%%
Productions
%%
User subroutines

一、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.

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/*
 * 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     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

二、gram.y定义部分源码

%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     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     select_no_parens select_with_parens select_clause
                simple_select values_clause
%type     alter_column_default opclass_item opclass_drop alter_using
%type     add_drop opt_asc_desc opt_nulls_order
%type     alter_table_cmd alter_type_cmd opt_collate_clause
       replica_identity partition_cmd index_partition_cmd
%type     alter_table_cmds alter_type_cmds
%type     alter_identity_column_option_list
%type   alter_identity_column_option
%type     opt_drop_behavior
%type     createdb_opt_list createdb_opt_items copy_opt_list
                transaction_mode_list
                create_extension_opt_list alter_extension_opt_list
%type     createdb_opt_item copy_opt_item
                transaction_mode_item
                create_extension_opt_item alter_extension_opt_item
%type     opt_lock lock_type cast_context
%type     vacuum_option_list vacuum_option_elem
                analyze_option_list analyze_option_elem
%type     opt_or_replace
                opt_grant_grant_option opt_grant_admin_option
                opt_nowait opt_if_exists opt_with_data
%type     opt_nowait_or_skip
%type     OptRoleList AlterOptRoleList
%type     CreateOptRoleElem AlterOptRoleElem
%type         opt_type
%type         foreign_server_version opt_foreign_server_version
%type         opt_in_database
%type         OptSchemaName
%type     OptSchemaEltList
%type  TriggerForSpec TriggerForType
%type     TriggerActionTime
%type     TriggerEvents TriggerOneEvent
%type     TriggerFuncArg
%type     TriggerWhen
%type         TransitionRelName
%type     TransitionRowOrTable TransitionOldOrNew
%type     TriggerTransition
%type     event_trigger_when_list event_trigger_value_list
%type     event_trigger_when_item
%type         enable_trigger
%type         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     func_name handler_name qual_Op qual_all_Op subquery_Op
                opt_class opt_inline_handler opt_validator validator_clause
                opt_collate
%type     qualified_name insert_target OptConstrFromTable
%type         all_Op MathOp
%type         row_security_cmd RowSecurityDefaultForCmd
%type  RowSecurityDefaultPermissive
%type     RowSecurityOptionalWithCheck RowSecurityOptionalExpr
%type     RowSecurityDefaultToRole RowSecurityOptionalToRole
%type         iso_level opt_encoding
%type  grantee
%type     grantee_list
%type  privilege
%type     privileges privilege_list
%type  privilege_target
%type  function_with_argtypes aggregate_with_argtypes operator_with_argtypes
%type     function_with_argtypes_list aggregate_with_argtypes_list operator_with_argtypes_list
%type     defacl_privilege_target
%type     DefACLOption
%type     DefACLOptionList
%type     import_qualification_type
%type  import_qualification
%type     vacuum_relation
%type     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     group_by_list
%type     group_by_item empty_grouping_set rollup_clause cube_clause
%type     grouping_sets_clause
%type     opt_publication_for_tables publication_for_tables
%type     publication_name_item
%type     opt_fdw_options fdw_options
%type     fdw_option
%type     OptTempTableName
%type     into_clause create_as_target create_mv_target
%type     createfunc_opt_item common_func_opt_item dostmt_opt_item
%type  func_arg func_arg_with_default table_func_column aggr_arg
%type  arg_class
%type     func_return func_type
%type   opt_trusted opt_restart_seqs
%type      OptTemp
%type      OptNoLog
%type  OnCommitOption
%type     for_locking_strength
%type     for_locking_item
%type     for_locking_clause opt_for_locking_clause for_locking_items
%type     locked_rels_list
%type     all_or_distinct
%type     join_outer join_qual
%type     join_type
%type     extract_list overlay_list position_list
%type     substr_list trim_list
%type     opt_interval interval_second
%type     overlay_placing substr_from substr_for
%type  opt_instead
%type  opt_unique opt_concurrently opt_verbose opt_full
%type  opt_freeze opt_analyze opt_default opt_recheck
%type     opt_binary opt_oids copy_delimiter
%type  copy_from opt_program
%type     opt_column event cursor_options opt_hold opt_set_data
%type     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     fetch_args limit_clause select_limit_value
                offset_clause select_offset_value
                select_fetch_first_value I_or_F_const
%type     row_or_rows first_or_next
%type     OptSeqOptList SeqOptList OptParenthesizedSeqOptList
%type     SeqOptElem
%type     insert_rest
%type     opt_conf_expr
%type  opt_on_conflict
%type  generic_set set_rest set_rest_more generic_reset reset_rest
                 SetResetClause FunctionSetResetClause
%type     TableElement TypedTableElement ConstraintElem TableFuncElement
%type     columnDef columnOptions
%type     def_elem reloption_elem old_aggr_elem operator_def_elem
%type     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     rowsfrom_item rowsfrom_list opt_col_def_list
%type  opt_ordinality
%type     ExclusionConstraintList ExclusionConstraintElem
%type     func_arg_list
%type     func_arg_expr
%type     row explicit_row implicit_row type_list array_expr_list
%type     case_expr case_arg when_clause case_default
%type     when_clause_list
%type     sub_type
%type     NumericOnly
%type     NumericOnly_list
%type     alias_clause opt_alias_clause
%type     func_alias_clause
%type     sortby
%type     index_elem
%type     table_ref
%type     joined_table
%type     relation_expr
%type     relation_expr_opt_alias
%type     tablesample_clause opt_repeatable_clause
%type     target_el set_target insert_column_item
%type         generic_option_name
%type     generic_option_arg
%type     generic_option_elem alter_generic_option_elem
%type     generic_option_list alter_generic_option_list
%type         explain_option_name
%type     explain_option_arg
%type     explain_option_elem
%type     explain_option_list
%type     reindex_target_type reindex_target_multitable
%type     reindex_option_list reindex_option_elem
%type     copy_generic_opt_arg copy_generic_opt_arg_list_item
%type     copy_generic_opt_elem
%type     copy_generic_opt_list copy_generic_opt_arg_list
%type     copy_options
%type     Typename SimpleTypename ConstTypename
                GenericType Numeric opt_float
                Character ConstCharacter
                CharacterWithLength CharacterWithoutLength
                ConstDatetime ConstInterval
                Bit ConstBit BitWithLength BitWithoutLength
%type         character
%type         extract_arg
%type  opt_varying opt_timezone opt_no_inherit
%type     Iconst SignedIconst
%type         Sconst comment_text notify_payload
%type         RoleId opt_boolean_or_string
%type     var_list
%type         ColId ColLabel var_name type_function_name param_name
%type         NonReservedWord NonReservedWord_or_Sconst
%type         createdb_opt_name
%type     var_value zone_value
%type  auth_ident RoleSpec opt_granted_by
%type  unreserved_keyword type_func_name_keyword
%type  col_name_keyword reserved_keyword
%type     TableConstraint TableLikeClause
%type     TableLikeOptionList TableLikeOption
%type     ColQualList
%type     ColConstraint ColConstraintElem ConstraintAttr
%type     key_actions key_delete key_match key_update key_action
%type     ConstraintAttributeSpec ConstraintAttributeElem
%type         ExistingIndex
%type     constraints_set_list
%type  constraints_set_mode
%type         OptTableSpace OptConsTableSpace
%type  OptTableSpaceOwner
%type     opt_check_option
%type         opt_provider security_label
%type     xml_attribute_el
%type     xml_attribute_list xml_attributes
%type     xml_root_version opt_xml_root_standalone
%type     xmlexists_argument
%type     document_or_content
%type  xml_whitespace_option
%type     xmltable_column_list xmltable_column_option_list
%type     xmltable_column_el
%type     xmltable_column_option_el
%type     xml_namespace_list
%type     xml_namespace_el
%type     func_application func_expr_common_subexpr
%type     func_expr func_expr_windowless
%type     common_table_expr
%type     with_clause opt_with_clause
%type     cte_list
%type     within_group_clause
%type     filter_clause
%type     window_clause window_definition_list opt_partition_clause
%type     window_definition over_clause window_specification
                opt_frame_clause frame_extent frame_bound
%type     opt_window_exclusion_clause
%type         opt_existing_window_name
%type  opt_if_not_exists
%type     generated_when override_kind
%type     PartitionSpec OptPartitionSpec
%type             part_strategy
%type     part_elem
%type         part_params
%type  PartitionBoundSpec
%type         partbound_datum PartitionRangeDatum
%type         hash_partbound partbound_datum_list range_datum_list
%type         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!
 * 非关键字token类型.
 * 这些都被硬链接到"flex"的词法分析器中.
 * 必须首先列出这些token,这样他们的数字代码就不用依赖关键字集合了.
 * PL/pgsQL依赖于该集合以便可以共享相同的词法分析器.
 * 如果在这里添加/修改tokens,那么注意相应的修改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语法中不会使用,因此通常会提示解析错误.用于PL/pgSQL.
 */
%token     IDENT FCONST SCONST BCONST XCONST Op
%token     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".
 * 如果希望修改关键字,更新src/include/parser/kwlist.h,
 *   同时在下面的关键字列表中在合适的位置添加新的关键字.可在文件中搜索"Keyword category lists"
 */
/* ordinary key words in alphabetical order */
//以字母顺序排列的普通关键字.
%token  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).
 * 语法分析器认为存在关键字,但这些关键字没有在kwlist.h中列出,因此永远都不能直接进入.
 * parser.c中的过滤器在需要的时候创建这些tokens(基于提前查看一个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之所以存在以便诸如NOT LIKE这样的产生式可与LIKE具备同样的优先顺序.
 * 否则它们会与NOT的优先级一样,至少对于他们的左子表达式如此.
 * NULLS_LA和WITH_LA用于产生LALR(1)语法解析器.
 */
%token        NOT_LA NULLS_LA WITH_LA
/* Precedence: lowest to highest */
//优先级:从低到高
%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
//转义操作
%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.
 * 为了支持没有AS的target_el,必须在POSTFIXOP和Op之间明确的给IDENT一个显式的优先级.
 * 我们可以根据需要安全地为各种未保留的关键字分配相同的优先级,以解决歧义.
 * (这不会有什么不好的影响,因为显然的,关键字的行为与它们不是关键字是一样的).
 * 我们需要做的事情是:
 *   对于PARTITION, RANGE, ROWS, GROUPS,需要支持opt_existing_window_name;
 *   对于RANGE, ROWS, GROUPS,以便它们可以跟随a_expr而不会产生后缀操作符问题;
 *   对于GENERATED,可以跟随b_expr;
 *   对于NULL,可以在ColQualList中跟随b_expr而不会产生后缀操作符问题;
 *
 * 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中支持CUBE/ROLLUP而无需保留它们,我们给予它们显示的优先级,要低于字符'(',
 *   这样存在CUBE '('的规则会进行状态转换而不是把CUBE视为函数名称而产生折叠冲突的规则.
 * 基于以上的理由,使用与IDENT相同的优先级似乎是正确的.
 *
 * 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产生式UNBOUNDED PRECEDING和UNBOUNDED FOLLOWING更加混乱:
 * 因为UNBOUNDED是非保留关键字(per spec!),不存在明确的原则来区分产生式.
 * 通过给UNBOUNDED的优先级比PRECEDING和FOLLOWING更低优先级来解决此问题.
 * 到现在为止,看起来不会产生把UNBOUNDED与语法中其他任何地方的非保留关键字区别对待,
 *   但这肯定存在风险.
 * 不过,我们可以将UNBOUNDED的任何有趣行为归咎于SQL标准。
 *
 */
//理想的情况下不应存在于IDENT相同的优先级.
%nonassoc    UNBOUNDED        /* ideally should have same precedence as IDENT */
%nonassoc    IDENT GENERATED NULL_P PARTITION RANGE ROWS GROUPS PRECEDING FOLLOWING CUBE ROLLUP
//多字符组成的操作符和用户自定义操作符
%left        Op OPERATOR        /* multi-character ops and user-defined operators */
%left        '+' '-'
%left        '*' '/' '%'
%left        '^'
/* Unary Operators */
//一元运算符
%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.
 * 这些操作符看起来优先级比较低,但实际上在把它们作为连接操作符时,
 *   它们根本不是算术层次结构的一部分.
 * 提高它们的优先级,可以支持将它们用作函数名称.
 * 如果我们不需要连接规则本身的左结合性,它们根本就不会被授予优先级.
 */
%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引起的转移/折叠冲突.
%right        PRESERVE STRIP_P

三、参考资料

Flex&Bison