SQLite3判断Token类型（Keyword）

SQLite3的getToken函数负责判断SQL语句中的Token（语素），并返回该Token的长度。一些基本的Token（如运算符，括号等）放在了冗长的Switch...case里。对keyword的判断提到了keywordCode里，其中竟包含了一个HashTable结构:

Hash函数：( ( toLower(z[0])*4 ) ^ ( toLower(z[n-1])*3 ) ^ n ) % 127

冲突解决：aNext数组

为了查找提高速度，先使用aLen比较长度。在实现toLower()时，使用charMap映射表，避免了If的判断。

static int keywordCode(const char *z,int n){ static const char zText[537] = "ABORTABLEFTEMPORARYADDATABASELECTHENDEFAULTRANSACTIONATURALTER" "AISEACHECKEYAFTEREFERENCESCAPELSEXCEPTRIGGEREGEXPLAINITIALLYANALYZE" "XCLUSIVEXISTSTATEMENTANDEFERRABLEATTACHAVINGLOBEFOREIGNOREINDEX" "AUTOINCREMENTBEGINNERENAMEBETWEENOTNULLIKEBYCASCADEFERREDELETE" "CASECASTCOLLATECOLUMNCOMMITCONFLICTCONSTRAINTERSECTCREATECROSS" "CURRENT_DATECURRENT_TIMESTAMPLANDESCDETACHDISTINCTDROPRAGMATCH" "FAILIMITFROMFULLGROUPDATEIFIMMEDIATEINSERTINSTEADINTOFFSETISNULL" "JOINORDEREPLACEOUTERESTRICTPRIMARYQUERYRIGHTROLLBACKROWHENUNION" "UNIQUEUSINGVACUUMVALUESVIEWHERE"; static const unsigned char aHash[127] = { 92,80,107,91,4,114,83,95,44,76,93,106,109,97,90,10,113,110,103,28,48,41,65,71,63,19,105,36,104,108,74,33,61,37,8,115,38,12,77,40,25,66,31,81,53,30,50,20,88,34,75,26,72,64,47,67,22,87,29,69,86,1,9,101,58,18,112,82,99,54,6,85,49,94,102,70,15,116,51,56,2,55,111,}; static const unsigned char aNext[116] = { 0,3,17,11,5,13,7,43,16,23,52,45,59,73,42,24,60,21,79,68,84,46,39,96,98,100,32,14,27,78,57,89,35,62,}; static const unsigned char aLen[116] = { 5,}; static const unsigned short int aOffset[116] = { 0,118,122,128,136,141,150,152,162,167,172,175,177,181,185,187,192,194,196,205,208,212,218,224,227,230,234,236,237,241,248,254,258,262,269,275,281,289,296,305,311,316,328,344,348,352,358,359,366,369,373,378,381,386,390,394,397,403,405,414,420,427,430,433,436,442,446,450,457,461,469,476,481,486,494,496,500,505,511,516,522,528,531,}; static const unsigned char aCode[116] = { TK_ABORT,TK_TABLE,TK_JOIN_KW,TK_TEMP,TK_OR,TK_ADD,TK_DATABASE,TK_AS,TK_SELECT,TK_THEN,TK_END,TK_DEFAULT,TK_TRANSACTION,TK_ON,TK_ALTER,TK_RAISE,TK_EACH,TK_CHECK,TK_KEY,TK_AFTER,TK_REFERENCES,TK_ESCAPE,TK_ELSE,TK_EXCEPT,TK_TRIGGER,TK_LIKE_KW,TK_EXPLAIN,TK_INITIALLY,TK_ALL,TK_ANALYZE,TK_EXCLUSIVE,TK_EXISTS,TK_STATEMENT,TK_AND,TK_DEFERRABLE,TK_ATTACH,TK_HAVING,TK_BEFORE,TK_FOR,TK_FOREIGN,TK_IGNORE,TK_REINDEX,TK_INDEX,TK_AUTOINCR,TK_TO,TK_IN,TK_BEGIN,TK_RENAME,TK_BETWEEN,TK_NOT,TK_NOTNULL,TK_NULL,TK_BY,TK_CASCADE,TK_ASC,TK_DEFERRED,TK_DELETE,TK_CASE,TK_CAST,TK_COLLATE,TK_COLUMNKW,TK_COMMIT,TK_CONFLICT,TK_CONSTRAINT,TK_INTERSECT,TK_CREATE,TK_CTIME_KW,TK_PLAN,TK_DESC,TK_DETACH,TK_DISTINCT,TK_IS,TK_DROP,TK_PRAGMA,TK_MATCH,TK_FAIL,TK_LIMIT,TK_FROM,TK_GROUP,TK_UPDATE,TK_IF,TK_IMMEDIATE,TK_INSERT,TK_INSTEAD,TK_INTO,TK_OF,TK_OFFSET,TK_SET,TK_ISNULL,TK_JOIN,TK_ORDER,TK_REPLACE,TK_RESTRICT,TK_PRIMARY,TK_QUERY,TK_ROLLBACK,TK_ROW,TK_WHEN,TK_UNION,TK_UNIQUE,TK_USING,TK_VACUUM,TK_VALUES,TK_VIEW,TK_WHERE,}; int h,i; if( n<2 ) return TK_ID; h = ((charMap(z[0])*4) ^ (charMap(z[n-1])*3) ^ n) % 127; for(i=((int)aHash[h])-1; i>=0; i=((int)aNext[i])-1){ if( aLen[i]==n && sqlite3StrNICmp(&zText[aOffset[i]],z,n)==0 ){ return aCode[i]; } } return TK_ID; }

（编辑：李大同）

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