SQLite

  char *zExpr;                    /* Text for indexed expression */
  int bDesc;                      /* True for DESC columns, otherwise false */
  int bKey;                       /* Part of index, not PK */
};

typedef struct CidxIndex CidxIndex;
struct CidxIndex {
  char *zWhere;                   /* WHERE clause, if any */
  int nCol;                       /* Elements in aCol[] array */
  CidxColumn aCol[1];             /* Array of indexed columns */
};

static void *cidxMalloc(int *pRc, int n){
  void *pRet = 0;
  assert( n!=0 );

static void cidxFreeIndex(CidxIndex *pIdx){
  if( pIdx ){
    int i;
    for(i=0; i<pIdx->nCol; i++){
      sqlite3_free(pIdx->aCol[i].zExpr);
    }
    sqlite3_free(pIdx->zWhere);
    sqlite3_free(pIdx);
  }
}

static int cidx_isspace(char c){
  return c==' ' || c=='\t' || c=='\r' || c=='\n';
}

static int cidx_isident(char c){
  return c<0 
    || (c>='0' && c<='9') || (c>='a' && c<='z') 
    || (c>='A' && c<='Z') || c=='_';
}

#define CIDX_PARSE_EOF   0
#define CIDX_PARSE_COMMA 1      /*  "," */
#define CIDX_PARSE_OPEN  2      /*  "(" */
#define CIDX_PARSE_CLOSE 3      /*  ")" */

/*
** Argument zIn points into the start, middle or end of a CREATE INDEX
** statement. If argument pbDoNotTrim is non-NULL, then this function
** scans the input until it finds EOF, a comma (",") or an open or
** close parenthesis character. It then sets (*pzOut) to point to said
** character and returns a CIDX_PARSE_XXX constant as appropriate. The
** parser is smart enough that special characters inside SQL strings
** or comments are not returned for.
**
** Or, if argument pbDoNotTrim is NULL, then this function sets *pzOut
** to point to the first character of the string that is not whitespace
** or part of an SQL comment and returns CIDX_PARSE_EOF.
**
** Additionally, if pbDoNotTrim is not NULL and the element immediately
** before (*pzOut) is an SQL comment of the form "-- comment", then
** (*pbDoNotTrim) is set before returning. In all other cases it is
** cleared.
*/
static int cidxFindNext(
  const char *zIn, 
  const char **pzOut,
  int *pbDoNotTrim                /* OUT: True if prev is -- comment */
){
  const char *z = zIn;

  while( 1 ){
    while( cidx_isspace(*z) ) z++;
    if( z[0]=='-' && z[1]=='-' ){
      z += 2;
      while( z[0]!='\n' ){
        if( z[0]=='\0' ) return CIDX_PARSE_EOF;
        z++;
      }
      while( cidx_isspace(*z) ) z++;
      if( pbDoNotTrim ) *pbDoNotTrim = 1;
    }else
    if( z[0]=='/' && z[1]=='*' ){
      z += 2;
      while( z[0]!='*' || z[1]!='/' ){
        if( z[1]=='\0' ) return CIDX_PARSE_EOF;
        z++;
      }
      z += 2;
    }else{
      *pzOut = z;
      if( pbDoNotTrim==0 ) return CIDX_PARSE_EOF;
      switch( *z ){
        case '\0':
          return CIDX_PARSE_EOF;
        case '(':
          return CIDX_PARSE_OPEN;
        case ')':
          return CIDX_PARSE_CLOSE;

          break;
        }
  
        case '[':
          while( *z++!=']' );
          break;
  











        default:
          z++;
          break;
      }
      *pbDoNotTrim = 0;
    }
  }

      pCol++;
      z = z1 = z2+1;
    }
    if( e==CIDX_PARSE_OPEN ) nParen++;
    if( e==CIDX_PARSE_CLOSE ) nParen--;
    z++;
  }

  /* Search for a WHERE clause */
  cidxFindNext(z, &z, 0);
  if( 0==sqlite3_strnicmp(z, "where", 5) ){
    pIdx->zWhere = cidxMprintf(&rc, "%s\n", &z[5]);
  }else if( z[0]!='\0' ){
    goto parse_error;
  }

  return rc;

 parse_error:
  cidxCursorError(pCsr, "Parse error in: %s", zSql);
  return SQLITE_ERROR;
}

        p->bKey = sqlite3_column_int(pInfo, 5);
        if( zSql==0 || p->bKey==0 ){
          p->zExpr = cidxMprintf(&rc, "\"%w\" COLLATE %s",zName,zColl);
        }else{
          p->zExpr = 0;
        }
        pIdx->nCol = iCol;
        pIdx->zWhere = 0;
      }
      cidxFinalize(&rc, pInfo);
    }

    if( rc==SQLITE_OK && zSql ){
      rc = cidxParseSQL(pCsr, pIdx, zSql);
    }

  zSubExpr = cidxColumnList(&rc, zIdxName, pIdx, CIDX_CLIST_SUBEXPR);
  zSrcList = cidxColumnList(&rc, zIdxName, pIdx, CIDX_CLIST_ALL);

  if( rc==SQLITE_OK && zAfterKey ){
    rc = cidxDecodeAfter(pCsr, pIdx->nCol, zAfterKey, &azAfter);
  }

  if( rc==SQLITE_OK ){
    if( zAfterKey==0 ){
      *pzSqlOut = cidxMprintf(&rc,
          "SELECT (SELECT %s FROM %Q AS t WHERE %s), %s "
          "FROM (SELECT %s FROM %Q INDEXED BY %Q %s%sORDER BY %s) AS i",
          zSubExpr, zTab, zSubWhere, zCurrentKey, 
          zSrcList, zTab, zIdxName, 
          (pIdx->zWhere ? "WHERE " : ""), (pIdx->zWhere ? pIdx->zWhere : ""),
          zOrderBy
      );
    }else{
      const char *zSep = "";
      char *zSql;
      int i;
  
      zSql = cidxMprintf(&rc, 
          "SELECT (SELECT %s FROM %Q WHERE %s), %s FROM (",
          zSubExpr, zTab, zSubWhere, zCurrentKey
      );
      for(i=pIdx->nCol-1; i>=0; i--){
        int j;
        if( pIdx->aCol[i].bDesc && azAfter[i]==0 ) continue;
        for(j=0; j<2; j++){
          char *zWhere = cidxWhere(&rc, pIdx->aCol, azAfter, i, j);
          zSql = cidxMprintf(&rc, "%z"
              "%sSELECT * FROM ("
                "SELECT %s FROM %Q INDEXED BY %Q WHERE %s%s%z ORDER BY %s"
              ")",
              zSql, zSep, zSrcList, zTab, zIdxName, 
              pIdx->zWhere ? pIdx->zWhere : "",
              pIdx->zWhere ? " AND " : "",
              zWhere, zOrderBy
          );
          zSep = " UNION ALL ";
          if( pIdx->aCol[i].bDesc==0 ) break;
        }
      }
      *pzSqlOut = cidxMprintf(&rc, "%z) AS i", zSql);
    }
  }

  sqlite3_free(zTab);
  sqlite3_free(zCurrentKey);
  sqlite3_free(zOrderBy);
  sqlite3_free(zSubWhere);
  sqlite3_free(zSubExpr);

  SELECT errmsg IS NULL, current_key, index_name, after_key, scanner_sql
    FROM incremental_index_check('i1') LIMIT 1;
} {
  1
  'five',5
  i1
  {}
  {SELECT (SELECT a IS i.i0 FROM 't1' AS t WHERE "rowid" COLLATE BINARY IS i.i1), quote(i0)||','||quote(i1) FROM (SELECT (a) AS i0, ("rowid" COLLATE BINARY) AS i1 FROM 't1' INDEXED BY 'i1' ORDER BY 1,2) AS i}
}

do_index_check_test 1.3 i1 {
  {} 'five',5
  {} 'four',4
  {} 'one',1
  {} 'three',3

  {} 3,2,1 
  {} 6,5,4
}
do_index_check_test 6.2 t6x3 {
  {} 3,2,1 
  {} 6,5,4
}

#-------------------------------------------------------------------------
#
do_execsql_test 7.0 {
  CREATE TABLE t7(x INTEGER PRIMARY KEY, y, z);
  INSERT INTO t7 VALUES(1, 1, 1);
  INSERT INTO t7 VALUES(2, 2, 0);
  INSERT INTO t7 VALUES(3, 3, 1);
  INSERT INTO t7 VALUES(4, 4, 0);

  CREATE INDEX t7i1 ON t7(y) WHERE z=1;
  CREATE INDEX t7i2 ON t7(y) /* hello,world */ WHERE z=1;
  CREATE INDEX t7i3 ON t7(y) WHERE -- yep 
  z=1;
  CREATE INDEX t7i4 ON t7(y) WHERE z=1 -- yep;
}
do_index_check_test 7.1 t7i1 {
  {} 1,1 {} 3,3
}
do_index_check_test 7.2 t7i2 {
  {} 1,1 {} 3,3
}
do_index_check_test 7.3 t7i3 {
  {} 1,1 {} 3,3
}
do_index_check_test 7.4 t7i4 {
  {} 1,1 {} 3,3
}