本篇内容主要讲解“PostgreSQL中的Declarations有什么作用”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“PostgreSQL中的Declarations有什么作用”吧!
PG利用Bison对语法进行分析,Bison输入文件由以下四部分组成:
%{
Declarations
%}
Definitions
%%
Productions
%%
User subroutinesDeclarations
Declarations与Flex类似,Bison会把这些代码原样拷贝到相应的c文件中(默认为y.tab.c,PG中是gram.c).
名词解释:
terminal symbols —> 终结符
non-terminals symbols —> 非终结符
reduce —> 折叠动作,输入为符合集合(终结符/非终结符),输出为匹配该pattern的非终结符
production —> 产生式,比如S -> S E,成为产生式
%{
#include "postgres.h"
#include <ctype.h>
#include <limits.h>
#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"
#define YYLLOC_DEFAULT(Current, Rhs, N) \
do { \
if ((N) > 0) \
(Current) = (Rhs)[1]; \
else \
(Current) = (-1); \
} while (0)
#define YYMALLOC palloc
#define YYFREE pfree
//privilege_target产生式结果的私有结构体
typedef struct PrivTarget
{
GrantTargetType targtype;
ObjectType objtype;
List *objs;
} PrivTarget;
//私有结构体 --> import_qualification产生式
typedef struct ImportQual
{
ImportForeignSchemaType type;
List *table_names;
} ImportQual;
//ConstraintAttributeSpec产生这些标志的整数位掩码
#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, 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);
static Node *makeIntConst(int val, int location);
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(List *indirection, core_yyscan_t yyscanner);
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);
%}到此，相信大家对“PostgreSQL中的Declarations有什么作用”有了更深的了解，不妨来实际操作一番吧！这里是亿速云网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习！
