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, 0, 4, 0, 0, 114, 0, 83, 0, 0, 95, 44, 76, 93, 0, 106, 109, 97, 90, 0, 10, 0, 0, 113, 0, 110, 103, 0, 28, 48, 0, 41, 0, 0, 65, 71, 0, 63, 19, 0, 105, 36, 104, 0, 108, 74, 0, 0, 33, 0, 61, 37, 0, 8, 0, 115, 38, 12, 0, 77, 40, 25, 66, 0, 0, 31, 81, 53, 30, 50, 20, 88, 0, 34, 0, 75, 26, 0, 72, 0, 0, 0, 64, 47, 67, 22, 87, 29, 69, 86, 0, 1, 0, 9, 101, 58, 18, 0, 112, 82, 99, 54, 6, 85, 0, 0, 49, 94, 0, 102, 0, 70, 0, 0, 15, 0, 116, 51, 56, 0, 2, 55, 0, 111, }; static const unsigned char aNext[116] = { 0, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 17, 0, 0, 0, 0, 0, 11, 0, 0, 0, 0, 5, 13, 0, 7, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 43, 0, 0, 0, 0, 0, 0, 0, 16, 0, 23, 52, 0, 0, 0, 0, 45, 0, 59, 0, 0, 0, 0, 0, 0, 0, 0, 73, 42, 0, 24, 60, 21, 0, 79, 0, 0, 68, 0, 0, 84, 46, 0, 0, 0, 0, 0, 0, 0, 0, 39, 96, 98, 0, 0, 100, 0, 32, 0, 14, 27, 78, 0, 57, 89, 0, 35, 0, 62, 0, }; static const unsigned char aLen[116] = { 5, 5, 4, 4, 9, 2, 3, 8, 2, 6, 4, 3, 7, 11, 2, 7, 5, 5, 4, 5, 3, 5, 10, 6, 4, 6, 7, 6, 7, 9, 3, 7, 9, 6, 9, 3, 10, 6, 6, 4, 6, 3, 7, 6, 7, 5, 13, 2, 2, 5, 5, 6, 7, 3, 7, 4, 4, 2, 7, 3, 8, 6, 4, 4, 7, 6, 6, 8, 10, 9, 6, 5, 12, 12, 17, 4, 4, 6, 8, 2, 4, 6, 5, 4, 5, 4, 4, 5, 6, 2, 9, 6, 7, 4, 2, 6, 3, 6, 4, 5, 7, 5, 8, 7, 5, 5, 8, 3, 4, 5, 6, 5, 6, 6, 4, 5, }; static const unsigned short int aOffset[116] = { 0, 4, 7, 10, 10, 14, 19, 21, 26, 27, 32, 34, 36, 42, 51, 52, 57, 61, 65, 67, 71, 74, 78, 86, 91, 94, 99, 105, 108, 113, 118, 122, 128, 136, 141, 150, 152, 162, 167, 172, 175, 177, 177, 181, 185, 187, 192, 194, 196, 205, 208, 212, 218, 224, 224, 227, 230, 234, 236, 237, 241, 248, 254, 258, 262, 269, 275, 281, 289, 296, 305, 311, 316, 328, 328, 344, 348, 352, 358, 359, 366, 369, 373, 378, 381, 386, 390, 394, 397, 403, 405, 414, 420, 427, 430, 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_TEMP, TK_OR, TK_ADD, TK_DATABASE, TK_AS, TK_SELECT, TK_THEN, TK_END, TK_DEFAULT, TK_TRANSACTION,TK_ON, TK_JOIN_KW, 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_LIKE_KW, TK_BEFORE, TK_FOR, TK_FOREIGN, TK_IGNORE, TK_REINDEX, TK_INDEX, TK_AUTOINCR, TK_TO, TK_IN, TK_BEGIN, TK_JOIN_KW, TK_RENAME, TK_BETWEEN, TK_NOT, TK_NOTNULL, TK_NULL, TK_LIKE_KW, 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_JOIN_KW, TK_CTIME_KW, TK_CTIME_KW, 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_JOIN_KW, 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_JOIN_KW, TK_RESTRICT, TK_PRIMARY, TK_QUERY, TK_JOIN_KW, 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;}