SQLite

  char *zDb;                      /* Database containing source table */
  char *zTab;                     /* Source table name */
  sqlite3_int64 iMin;             /* Minimum rowid */
  sqlite3_int64 iMax;             /* Maximum rowid */

  /* Fields used by swarmvtab only */
  char *zFile;                    /* File to ATTACH */
  int nUser;                      /* Current number of users */
  sqlite3 *db;                    /* Database handle */
  UnionSrc *pNextClosable;        /* Next in list of closable sources */
};

/*
** Virtual table  type for union vtab.
*/
struct UnionTab {
  sqlite3_vtab base;              /* Base class - must be first */
  sqlite3 *db;                    /* Database handle */
  int bSwarm;                     /* 1 for "swarmvtab", 0 for "unionvtab" */
  int iPK;                        /* INTEGER PRIMARY KEY column, or -1 */
  int nSrc;                       /* Number of elements in the aSrc[] array */

  UnionSrc *aSrc;                 /* Array of source tables, sorted by rowid */

  /* Used by swarmvtab only */
  char *zSourceStr;               /* Expected unionSourceToStr() value */
  UnionSrc *pClosable;            /* First in list of closable sources */
  int nOpen;                      /* Current number of open sources */
  int nMaxOpen;                   /* Maximum number of open sources */
};

/*
** Virtual table cursor type for union vtab.
*/
struct UnionCsr {
  sqlite3_vtab_cursor base;       /* Base class - must be first */
  sqlite3_stmt *pStmt;            /* SQL statement to run */

  /* Used by swarmvtab only */
  sqlite3_int64 iMaxRowid;        /* Last rowid to visit */
  int iTab;                       /* Index of table read by pStmt */
};

#define unionGetDb(pTab, pSrc) ((pTab)->bSwarm ? (pSrc)->db : (pTab)->db)

/*
** If *pRc is other than SQLITE_OK when this function is called, it
** always returns NULL. Otherwise, it attempts to allocate and return
** a pointer to nByte bytes of zeroed memory. If the memory allocation
** is attempted but fails, NULL is returned and *pRc is set to 
** SQLITE_NOMEM.

}

/*
** Call sqlite3_finalize() on SQL statement pStmt. If *pRc is set to 
** SQLITE_OK when this function is called, then it is set to the
** value returned by sqlite3_finalize() before this function exits.
*/
static void unionFinalize(int *pRc, sqlite3_stmt *pStmt, char **pzErr){
  sqlite3 *db = sqlite3_db_handle(pStmt);
  int rc = sqlite3_finalize(pStmt);
  if( *pRc==SQLITE_OK ){
    *pRc = rc;
    if( rc ){
      *pzErr = sqlite3_mprintf("%s", sqlite3_errmsg(db));
    }
  }
}

/*
** Close one database from the closable list.
*/
static int unionCloseDatabase(UnionTab *pTab, char **pzErr){

  int rc = SQLITE_OK;
  UnionSrc **pp;

  assert( pTab->pClosable && pTab->bSwarm );

  pp = &pTab->pClosable;
  while( (*pp)->pNextClosable ){
    pp = &(*pp)->pNextClosable;
  }






  assert( (*pp)->db );
  rc = sqlite3_close((*pp)->db);
  (*pp)->db = 0;
  *pp = 0;
  pTab->nOpen--;


  return rc;
}

/*
** xDisconnect method.
*/
static int unionDisconnect(sqlite3_vtab *pVtab){
  if( pVtab ){
    UnionTab *pTab = (UnionTab*)pVtab;
    int i;
    for(i=0; i<pTab->nSrc; i++){
      UnionSrc *pSrc = &pTab->aSrc[i];
      sqlite3_free(pSrc->zDb);
      sqlite3_free(pSrc->zTab);
      sqlite3_free(pSrc->zFile);


      sqlite3_close(pSrc->db);
    }

    sqlite3_free(pTab->zSourceStr);
    sqlite3_free(pTab->aSrc);
    sqlite3_free(pTab);
  }
  return SQLITE_OK;
}

  int *pRc,                       /* IN/OUT: Error code */
  UnionTab *pTab,                 /* Virtual table object */
  UnionSrc *pSrc,                 /* Source table to test */
  char **pzErr                    /* OUT: Error message */
){
  char *zRet = 0;
  if( *pRc==SQLITE_OK ){
    sqlite3 *db = unionGetDb(pTab, pSrc);
    int rc = unionIsIntkeyTable(db, pSrc, pzErr);
    if( rc==SQLITE_OK ){
      sqlite3_stmt *pStmt = unionPrepare(&rc, db, 
          "SELECT group_concat(quote(name) || '.' || quote(type)) "
          "FROM pragma_table_info(?, ?)", pzErr
      );


      sqlite3_bind_text(pStmt, 1, pSrc->zTab, -1, SQLITE_STATIC);
      sqlite3_bind_text(pStmt, 2, pSrc->zDb, -1, SQLITE_STATIC);
      if( SQLITE_ROW==sqlite3_step(pStmt) ){
        const char *z = (const char*)sqlite3_column_text(pStmt, 0);
        zRet = unionStrdup(&rc, z);
      }
      unionFinalize(&rc, pStmt, pzErr);
    }
    *pRc = rc;
  }

  return zRet;
}

/*
** Check that all configured source tables exist and have the same column
** names and datatypes. If this is not the case, or if some other error
** occurs, return an SQLite error code. In this case *pzErr may be set
** to point to an error message buffer allocated by sqlite3_mprintf().
** Or, if no problems regarding the source tables are detected and no
** other error occurs, SQLITE_OK is returned.
*/
static int unionSourceCheck(UnionTab *pTab, char **pzErr){
  int rc = SQLITE_OK;






  char *z0 = 0;
  int i;

  assert( *pzErr==0 );
  z0 = unionSourceToStr(&rc, pTab, &pTab->aSrc[0], pzErr);
  for(i=1; i<pTab->nSrc; i++){
    char *z = unionSourceToStr(&rc, pTab, &pTab->aSrc[i], pzErr);
    if( rc==SQLITE_OK && sqlite3_stricmp(z, z0) ){
      *pzErr = sqlite3_mprintf("source table schema mismatch");
      rc = SQLITE_ERROR;
    }
    sqlite3_free(z);
  }



  sqlite3_free(z0);

  return rc;
}

static int unionOpenDatabase(UnionTab *pTab, int iSrc, char **pzErr){
  int rc = SQLITE_OK;
  UnionSrc *pSrc = &pTab->aSrc[iSrc];

  assert( pTab->bSwarm && iSrc<pTab->nSrc );
  if( pSrc->db==0 ){

    while( rc==SQLITE_OK && pTab->pClosable && pTab->nOpen>=pTab->nMaxOpen ){

      rc = unionCloseDatabase(pTab, pzErr);
    }




    if( rc==SQLITE_OK ){

      rc = sqlite3_open(pSrc->zFile, &pSrc->db);

      if( rc!=SQLITE_OK ){
        *pzErr = sqlite3_mprintf("%s", sqlite3_errmsg(pSrc->db));
      }else{
        char *z = unionSourceToStr(&rc, pTab, pSrc, pzErr);
        if( rc==SQLITE_OK ){
          if( pTab->zSourceStr==0 ){
            pTab->zSourceStr = z;
          }else{
            if( sqlite3_stricmp(z, pTab->zSourceStr) ){
              *pzErr = sqlite3_mprintf("source table schema mismatch");
              rc = SQLITE_ERROR;
            }
            sqlite3_free(z);
          }
        }
      }

      if( rc==SQLITE_OK ){
        pSrc->pNextClosable = pTab->pClosable;
        pTab->pClosable = pSrc;
        pTab->nOpen++;
      }else{
        sqlite3_close(pSrc->db);
        pSrc->db = 0;
      }
    }
  }

  return rc;
}


/*
** This function is a no-op for unionvtab tables. For swarmvtab, increment 
** the reference count for source table iTab. If the reference count was
** zero before it was incremented, also remove the source from the closable
** list.
*/
static void unionIncrRefcount(UnionTab *pTab, int iTab){
  if( pTab->bSwarm ){
    UnionSrc *pSrc = &pTab->aSrc[iTab];
    assert( pSrc->nUser>=0 && pSrc->db );
    if( pSrc->nUser==0 ){
      UnionSrc **pp;
      for(pp=&pTab->pClosable; *pp!=pSrc; pp=&(*pp)->pNextClosable);
      *pp = pSrc->pNextClosable;
      pSrc->pNextClosable = 0;
    }
    pSrc->nUser++;
  }
}

/*
** Finalize the SQL statement pCsr->pStmt and return the result.
**
** If this is a swarmvtab table (not unionvtab) and pCsr->pStmt was not
** NULL when this function was called, also decrement the reference
** count on the associated source table. If this means the source tables
** refcount is now zero, add it to the closable list.
*/
static int unionFinalizeCsrStmt(UnionCsr *pCsr){
  int rc = SQLITE_OK;
  if( pCsr->pStmt ){
    UnionTab *pTab = (UnionTab*)pCsr->base.pVtab;
    UnionSrc *pSrc = &pTab->aSrc[pCsr->iTab];
    rc = sqlite3_finalize(pCsr->pStmt);
    pCsr->pStmt = 0;
    if( pTab->bSwarm ){
      pSrc->nUser--;
      assert( pSrc->nUser>=0 );
      if( pSrc->nUser==0 ){
        pSrc->pNextClosable = pTab->pClosable;
        pTab->pClosable = pSrc;
      }
    }
  }
  return rc;
}



/* 
** xConnect/xCreate method.
**
** The argv[] array contains the following:
**
**   argv[0]   -> module name  ("unionvtab")

  sqlite3_vtab **ppVtab,
  char **pzErr
){
  UnionTab *pTab = 0;
  int rc = SQLITE_OK;
  int bSwarm = (pAux==0 ? 0 : 1);
  const char *zVtab = (bSwarm ? "swarmvtab" : "unionvtab");


  if( sqlite3_stricmp("temp", argv[1]) ){
    /* unionvtab tables may only be created in the temp schema */
    *pzErr = sqlite3_mprintf("%s tables must be created in TEMP schema", zVtab);
    rc = SQLITE_ERROR;
  }else if( argc!=4 ){
    *pzErr = sqlite3_mprintf("wrong number of arguments for %s", zVtab);

      if( rc==SQLITE_OK ){
        pSrc = &pTab->aSrc[pTab->nSrc++];
        pSrc->zTab = unionStrdup(&rc, zTab);
        pSrc->iMin = iMin;
        pSrc->iMax = iMax;
        if( bSwarm ){
          pSrc->zFile = unionStrdup(&rc, zDb);


        }else{
          pSrc->zDb = unionStrdup(&rc, zDb);

        }
      }
    }
    unionFinalize(&rc, pStmt, pzErr);
    pStmt = 0;

    /* It is an error if the SELECT statement returned zero rows. If only
    ** because there is no way to determine the schema of the virtual 
    ** table in this case.  */
    if( rc==SQLITE_OK && pTab->nSrc==0 ){
      *pzErr = sqlite3_mprintf("no source tables configured");
      rc = SQLITE_ERROR;
    }

    /* For unionvtab, verify that all source tables exist and have 
    ** compatible schemas. For swarmvtab, attach the first database and
    ** check that the first table is a rowid table only.  */
    if( rc==SQLITE_OK ){
      pTab->db = db;
      pTab->bSwarm = bSwarm;
      pTab->nMaxOpen = SWARMVTAB_MAX_ATTACHED;
      if( bSwarm ){
        rc = unionOpenDatabase(pTab, 0, pzErr);
      }else{
        rc = unionSourceCheck(pTab, pzErr);
      }
    }

    /* Compose a CREATE TABLE statement and pass it to declare_vtab() */
    if( rc==SQLITE_OK ){
      UnionSrc *pSrc = &pTab->aSrc[0];
      sqlite3 *tdb = unionGetDb(pTab, pSrc);
      pStmt = unionPreparePrintf(&rc, pzErr, tdb, "SELECT "
          "'CREATE TABLE xyz('"
          "    || group_concat(quote(name) || ' ' || type, ', ')"
          "    || ')',"
          "max((cid+1) * (type='INTEGER' COLLATE nocase AND pk=1))-1 "
          "FROM pragma_table_info(%Q, ?)", 
          pSrc->zTab, pSrc->zDb
      );
    }
    if( rc==SQLITE_OK && SQLITE_ROW==sqlite3_step(pStmt) ){
      const char *zDecl = (const char*)sqlite3_column_text(pStmt, 0);
      rc = sqlite3_declare_vtab(db, zDecl);
      pTab->iPK = sqlite3_column_int(pStmt, 1);
    }

    unionFinalize(&rc, pStmt, pzErr);
  }

  if( rc!=SQLITE_OK ){
    unionDisconnect((sqlite3_vtab*)pTab);
    pTab = 0;
  }

}

/*
** xClose
*/
static int unionClose(sqlite3_vtab_cursor *cur){
  UnionCsr *pCsr = (UnionCsr*)cur;
  unionFinalizeCsrStmt(pCsr);
  sqlite3_free(pCsr);
  return SQLITE_OK;
}


/*
** xNext
*/
static int doUnionNext(UnionCsr *pCsr){
  int rc = SQLITE_OK;
  assert( pCsr->pStmt );
  if( sqlite3_step(pCsr->pStmt)!=SQLITE_ROW ){
    UnionTab *pTab = (UnionTab*)pCsr->base.pVtab;

    rc = unionFinalizeCsrStmt(pCsr);
    if( rc==SQLITE_OK && pTab->bSwarm ){
      pCsr->iTab++;
      if( pCsr->iTab<pTab->nSrc ){
        UnionSrc *pSrc = &pTab->aSrc[pCsr->iTab];
        if( pCsr->iMaxRowid>=pSrc->iMin ){
          /* It is necessary to scan the next table. */
          sqlite3 *db;
          rc = unionOpenDatabase(pTab, pCsr->iTab, &pTab->base.zErrMsg);
          db = unionGetDb(pTab, pSrc);
          pCsr->pStmt = unionPreparePrintf(&rc, &pTab->base.zErrMsg, db,
              "SELECT rowid, * FROM %Q %s %lld",
              pSrc->zTab,
              (pSrc->iMax>pCsr->iMaxRowid ? "WHERE _rowid_ <=" : "-- "),
              pCsr->iMaxRowid
          );
          if( rc==SQLITE_OK ){
            assert( pCsr->pStmt );
            unionIncrRefcount(pTab, pCsr->iTab);
            rc = SQLITE_ROW;
          }
        }
      }
    }
  }

  return rc;
}

        }else{
          iMin++;
        }
      }
    }
  }


  unionFinalizeCsrStmt(pCsr);
  if( bZero ){
    return SQLITE_OK;
  }

  for(i=0; i<pTab->nSrc; i++){
    UnionSrc *pSrc = &pTab->aSrc[i];
    if( iMin>pSrc->iMax || iMax<pSrc->iMin ){

        zSql = sqlite3_mprintf("%z %s rowid<=%lld", zSql, zWhere, iMax);
      }
    }

    if( pTab->bSwarm ){
      pCsr->iTab = i;
      pCsr->iMaxRowid = iMax;
      rc = unionOpenDatabase(pTab, i, &pTab->base.zErrMsg);
      break;
    }
  }


  if( zSql==0 ){
    return rc;
  }else{
    sqlite3 *db = unionGetDb(pTab, &pTab->aSrc[pCsr->iTab]);
    pCsr->pStmt = unionPrepare(&rc, db, zSql, &pTab->base.zErrMsg);
    if( pCsr->pStmt ){
      unionIncrRefcount(pTab, pCsr->iTab);
    }
    sqlite3_free(zSql);
  }
  if( rc!=SQLITE_OK ) return rc;
  return unionNext(pVtabCursor);
}

/*
** xBestIndex.
**

ifcapable !vtab {
  finish_test
  return
}

load_static_extension db unionvtab

set nFile $sqlite_open_file_count

do_execsql_test 1.0 {
  CREATE TABLE t0(a INTEGER PRIMARY KEY, b TEXT);
  WITH s(i) AS ( SELECT 1 UNION ALL SELECT i+1 FROM s WHERE i<400) 
  INSERT INTO t0 SELECT i, hex(randomblob(50)) FROM s;

  CREATE TABLE dir(f, t, imin, imax);
}

      DETACH aux;
      INSERT INTO dir VALUES('test.db$i', 't$i', $iMin, $iMax);
    }]
  }

  execsql {
    CREATE VIRTUAL TABLE temp.s1 USING swarmvtab('SELECT * FROM dir');

  }
} {}

do_execsql_test 1.2 { 
  DROP TABLE s1; 

} {}

do_execsql_test 1.3 {
  CREATE VIRTUAL TABLE temp.s1 USING swarmvtab('SELECT * FROM dir');
  SELECT count(*) FROM s1 WHERE rowid<50;
} {49}

proc do_compare_test {tn where} {
  set sql [subst {
    SELECT (
        SELECT group_concat(a || ',' || b, ',') FROM t0 WHERE $where
    ) IS (
        SELECT group_concat(a || ',' || b, ',') FROM s1 WHERE $where
    )
  }]

  uplevel [list do_execsql_test $tn $sql 1]
}

do_compare_test 1.4 "rowid = 55"
do_compare_test 1.5 "rowid BETWEEN 20 AND 100"
do_compare_test 1.6 "rowid > 350"
do_compare_test 1.7 "rowid >= 350"
do_compare_test 1.8 "rowid >= 200"
do_compare_test 1.9 "1"
do_compare_test 1.10 "rowid = 700"
do_compare_test 1.11 "rowid = -1"
do_compare_test 1.12 "rowid = 0"


do_test 1.x {
  set sqlite_open_file_count
} [expr $nFile+9]

do_test 1.y { db close } {}


finish_test