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This article mainly explains "what is the role of Declarations in PostgreSQL". Interested friends may wish to have a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn "what is the role of Declarations in PostgreSQL"?

PG uses Bison to parse the syntax, and the Bison input file consists of the following four parts:

% {Declarations%} Definitions%%Productions%%User subroutinesDeclarations

Declarations is similar to Flex, Bison will copy the code to the corresponding c file as is (the default is y.tab.cjpg is gram.c).

The noun explains:

Terminal symbols-> Terminator

Non-terminals symbols-> non-Terminator

Reduce-> collapse action, input as match set (Terminator / non-Terminator), output as non-Terminator matching the pattern

Production-> production, such as S-> S E, becomes production.

% {/ * # define YYDEBUG 1 / PostgreSQL Global Development Group * POSTGRESQL BISON rules/actions * * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group * Portions Copyright (c) 1994 Regents of the University of California * IDENTIFICATION * src/backend/parser/gram.y * * HISTORY * AUTHOR DATE MAJOR EVENT * Andrew Yu Sept, 1994 POSTQUEL to SQL conversion * Andrew Yu Oct, 1994 lispy code conversion * * NOTES * CAPITALS are used to represent terminal symbols. * non-capitals are used to represent non-terminals. * * In general, nothing in this file should initiate database accesses * nor depend on changeable state (such as SET variables) If you do * database accesses, your code will fail when we have aborted the * current transaction and are just parsing commands to find the next * ROLLBACK or COMMIT. If you make use of SET variables, then you * will do the wrong thing in multi-query strings like this: * SET constraint_exclusion TO off; SELECT * FROM foo; * because the entire string is parsed by gram.y before the SET gets * executed. Anything that depends on the database or changeable state * should be handled during parse analysis so that it happens at the * right time not the wrong time. * * WARNINGS * If you use a list, make sure the datum is a node so that the printing * routines work. * * Sometimes we assign constants to makeStrings. Make sure we don't free * those. * Note * uppercase letters are used to indicate termination symbols. * non-uppercase letters are used to indicate non-terminal symbols. Summary symbols and non-terminating symbols in grammars generally speaking, the logic in this file should not enable database access and should not rely on changeable states (such as SET variables). * if you do need database access, the business code will make an error after rolling back the current transaction and then start parsing commands to find the next ROLLBACK/COMMIT. * if the SET variable is used, errors will occur in multiple query strings, such as: * SET constraint_exclusion TO off; SELECT * FROM foo; * because the entire string will be parsed by gram.y before SET execution * all events that depend on the database or variable state should be handled in the parsing phase so that they occur at the correct rather than the wrong time. * *-/ # include "postgres.h" # include # include # include "catalog/index.h" # include "catalog/namespace.h" # include "catalog/pg_am.h" # Include "catalog/pg_trigger.h" # include "commands/defrem.h" # include "commands/trigger.h" # include "nodes/makefuncs.h" # include "nodes/nodeFuncs.h" # include "parser/gramparse.h" # include "parser/parser.h" # include "parser/parse_expr.h" # include "storage/lmgr.h" # include "utils/date.h" # include "utils/datetime.h" # include "utils/numeric.h" # include "utils/xml.h" / * * Location tracking support-simpler than bison's default Since we only * want to track the start position not the end position of each nonterminal. * location tracking support-easier than bison default processing, because we only need to track the start position, not the end position of each non-Terminator. * / # define YYLLOC_DEFAULT (Current, Rhs, N)\ do {\ if (N) > 0)\ (Current) = (Rhs) [1];\ else\ (Current) = (- 1);\} while (0) / * * The above macro assigns-1 (unknown) as the parse location of any * nonterminal that was reduced from an empty rule, or whose leftmost * component was reduced from an empty rule. This is problematic * for nonterminals defined like * OptFooList: / * EMPTY * / {...} | OptFooList Foo {...}; * because we'll set-1 as the location during the first reduction and then * copy it during each subsequent reduction, leaving us with-1 for the * location even when the list is not empty. To fix that, do this in the * action for the nonempty rule (s): * if (@ $)

< 0) @$ = @2; * (Although we have many nonterminals that follow this pattern, we only * bother with fixing @$ like this when the nonterminal's parse location * is actually referenced in some rule.) * 上面的宏将-1(未知数)指定为所有非终结符的解析位置, * 这些非终结符是从空规则折叠(规约)而来的,或者其最左边的组件是从空规则折叠而来. * 对于下面的非终结符,存在问题: * OptFooList: / * EMPTY * / { ... } | OptFooList Foo { ... } ; * 因为在第一次折叠时将设置值为-1,然后在接下来的折叠中拷贝该值, * 这会让就算链表不为空也会一直让位置一直为-1. * 为了修正这一错误,对于非空规则,执行这一动作: * if (@$ < 0) @$ = @2; * * A cleaner answer would be to make YYLLOC_DEFAULT scan all the Rhs * locations until it's found one that's not -1. Then we'd get a correct * location for any nonterminal that isn't entirely empty. But this way * would add overhead to every rule reduction, and so far there's not been * a compelling reason to pay that overhead. * 更清晰的做法是让YYLLOC_DEFAULT扫描所有的Rhs位置直至找到不为-1为止. * 然后我们就可以为完全不为空的非终结符获取正确的位置. * 但这样的做法会增加每个规则折叠的负载,到目前为止,还没有一个令人信服的理由来增加开销. *//* * Bison doesn't allocate anything that needs to live across parser calls, * so we can easily have it use palloc instead of malloc. This prevents * memory leaks if we error out during parsing. Note this only works with * bison >

= 2.0. However, in bison 1.875 the default is to use alloca () * if possible, so there's not really much problem anyhow, at least if * you're building with gcc. * Bison does not allocate memory during parser calls, so we can easily use palloc instead of malloc. * this prevents memory leaks caused by errors during parsing. Note that this feature only works at 2.0 +. * in any case, in the bison 1.875 version, memory is allocated using alloca by default, and there are not many problems when building with gcc. * / # define YYMALLOC palloc#define YYFREE pfree/* Private struct for the result of privilege_target production * / / typedef struct PrivTarget {GrantTargetType targtype; ObjectType objtype; List * objs;} PrivTarget;/* Private struct for the result of import_qualification production * / Private structure of privilege_target production result-- > import_qualification production typedef struct ImportQual {ImportForeignSchemaType type; List * table_names;} ImportQual / * ConstraintAttributeSpec yields an integer bitmask of these flags: * / ConstraintAttributeSpec generates the integer bit mask # define CAS_NOT_DEFERRABLE 0x01#define CAS_DEFERRABLE 0x02#define CAS_INITIALLY_IMMEDIATE 0x04#define CAS_INITIALLY_DEFERRED 0x08#define CAS_NOT_VALID 0x10#define CAS_NO_INHERIT 0x20#define parser_yyerror (msg) scanner_yyerror (msg) of these flags Yyscanner) # define parser_errposition (pos) scanner_errposition (pos, yyscanner) static void base_yyerror (YYLTYPE * yylloc, core_yyscan_t yyscanner, const char * msg) Static RawStmt * makeRawStmt (Node * stmt, int stmt_location); static void updateRawStmtEnd (RawStmt * rs, int end_location); static Node * makeColumnRef (char * colname, List * indirection, int location, core_yyscan_t yyscanner); static Node * makeTypeCast (Node * arg, TypeName * typename, int location); static Node * makeStringConst (char * str, int location); static Node * makeStringConstCast (char * str, int location, TypeName * typename); typename * static Node (static Node, static Node) Static Node * makeFloatConst (char * str, int location); static Node * makeBitStringConst (char * str, int location); static Node * makeNullAConst (int location); static Node * makeAConst (Value * v, int location); static Node * makeBoolAConst (bool state, int location); static RoleSpec * makeRoleSpec (RoleSpecType type, int location); static void check_qualified_name (List * names, core_yyscan_t yyscanner); static List * check_func_name (List * names, core_yyscan_t yyscanner); static List * check_indirection (check_indirection * List, List) Static List * extractArgTypes (List * parameters); static List * extractAggrArgTypes (List * aggrargs); static List * makeOrderedSetArgs (List * directargs, List * orderedargs, core_yyscan_t yyscanner) Static void insertSelectOptions (SelectStmt * stmt, List * sortClause, List * lockingClause, Node * limitOffset, Node * limitCount, WithClause * withClause, core_yyscan_t yyscanner); static Node * makeSetOp (SetOperation op, bool all, Node * larg, Node * rarg) Static Node * doNegate (Node * n, int location); static void doNegateFloat (Value * v); static Node * makeAndExpr (Node * lexpr, Node * rexpr, int location); static Node * makeOrExpr (Node * lexpr, Node * rexpr, int location); static Node * makeNotExpr (Node * expr, int location); static Node * makeAArrayExpr (List * elements, int location); static Node * makeSQLValueFunction (SQLValueFunctionOp op, int32 typmod, int location) Static Node * makeXmlExpr (XmlExprOp op, char * name, List * named_args, List * args, int location); static List * mergeTableFuncParameters (List * func_args, List * columns); static TypeName * TableFuncTypeName (List * columns); static RangeVar * makeRangeVarFromAnyName (List * names, int position, core_yyscan_t yyscanner) Static void SplitColQualList (List * qualList, List * * constraintList, CollateClause * * collClause, core_yyscan_t yyscanner); static void processCASbits (int cas_bits, int location, const char * constrType, bool * deferrable, bool * initdeferred, bool * not_valid, bool * no_inherit, core_yyscan_t yyscanner); static Node * makeRecursiveViewSelect (char * relname, List * aliases, Node * query) %} at this point, I believe you have a deeper understanding of "what is the role of Declarations in PostgreSQL". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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