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Overview
Comment:Use randomness to prevent slowness in the generated-column-name uniqueness checking.
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SHA1: 6266712968a2cdcd6f5a3007d60c2cf1b3faf912
User & Date: drh 2015-11-14 16:47:23.463
Original Comment: Use randomness to prevent showness in the generated-column-name uniqueness checking.
Context
2015-11-14
20:52
Use a hash table to improve the preformance of column name uniqueness checking. (check-in: 5b08f29f45 user: drh tags: trunk)
16:47
Use randomness to prevent slowness in the generated-column-name uniqueness checking. (check-in: 6266712968 user: drh tags: trunk)
2015-11-13
20:52
Fix a memory leak in the fuzzcheck utility. (check-in: dfd6d9f4fb user: drh tags: trunk)
Changes
Side-by-Side Diff Ignore Whitespace Patch
Changes to src/select.c.
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  Parse *pParse,          /* Parsing context */
  ExprList *pEList,       /* Expr list from which to derive column names */
  i16 *pnCol,             /* Write the number of columns here */
  Column **paCol          /* Write the new column list here */
){
  sqlite3 *db = pParse->db;   /* Database connection */
  int i, j;                   /* Loop counters */
  int cnt;                    /* Index added to make the name unique */
  u32 cnt;                    /* Index added to make the name unique */
  Column *aCol, *pCol;        /* For looping over result columns */
  int nCol;                   /* Number of columns in the result set */
  Expr *p;                    /* Expression for a single result column */
  char *zName;                /* Column name */
  int nName;                  /* Size of name in zName[] */

  if( pEList ){
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    for(j=cnt=0; j<i; j++){
      if( sqlite3StrICmp(aCol[j].zName, zName)==0 ){
        char *zNewName;
        int k;
        for(k=nName-1; k>1 && sqlite3Isdigit(zName[k]); k--){}
        if( k>=0 && zName[k]==':' ) nName = k;
        zName[nName] = 0;
        zNewName = sqlite3MPrintf(db, "%s:%d", zName, ++cnt);
        zNewName = sqlite3MPrintf(db, "%s:%u", zName, ++cnt);
        sqlite3DbFree(db, zName);
        zName = zNewName;
        j = -1;
        if( zName==0 ) break;
        if( cnt>3 ) sqlite3_randomness(sizeof(cnt), &cnt);
      }
    }
    pCol->zName = zName;
  }
  if( db->mallocFailed ){
    for(j=0; j<i; j++){
      sqlite3DbFree(db, aCol[j].zName);
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