SQLite

    pDflt = 0;
  }

  /* Check that the new column is not specified as PRIMARY KEY or UNIQUE.
  ** If there is a NOT NULL constraint, then the default value for the
  ** column must not be NULL.
  */
  if( pCol->colFlags & COLFLAG_PRIMKEY ){
    sqlite3ErrorMsg(pParse, "Cannot add a PRIMARY KEY column");
    return;
  }
  if( pNew->pIndex ){
    sqlite3ErrorMsg(pParse, "Cannot add a UNIQUE column");
    return;
  }

    sqlite3ErrorMsg(pParse, 
      "table \"%s\" has more than one primary key", pTab->zName);
    goto primary_key_exit;
  }
  pTab->tabFlags |= TF_HasPrimaryKey;
  if( pList==0 ){
    iCol = pTab->nCol - 1;
    pTab->aCol[iCol].colFlags |= COLFLAG_PRIMKEY;
  }else{
    for(i=0; i<pList->nExpr; i++){
      for(iCol=0; iCol<pTab->nCol; iCol++){
        if( sqlite3StrICmp(pList->a[i].zName, pTab->aCol[iCol].zName)==0 ){
          break;
        }
      }
      if( iCol<pTab->nCol ){
        pTab->aCol[iCol].colFlags |= COLFLAG_PRIMKEY;
      }
    }
    if( pList->nExpr>1 ) iCol = -1;
  }
  if( iCol>=0 && iCol<pTab->nCol ){
    zType = pTab->aCol[iCol].zType;
  }

      /* Check if any parent key columns are being modified. */
      for(p=sqlite3FkReferences(pTab); p; p=p->pNextTo){
        for(i=0; i<p->nCol; i++){
          char *zKey = p->aCol[i].zCol;
          int iKey;
          for(iKey=0; iKey<pTab->nCol; iKey++){
            Column *pCol = &pTab->aCol[iKey];
            if( (zKey ? !sqlite3StrICmp(pCol->zName, zKey)
                      : (pCol->colFlags & COLFLAG_PRIMKEY)!=0) ){
              if( aChange[iKey]>=0 ) return 1;
              if( iKey==pTab->iPKey && chngRowid ) return 1;
            }
          }
        }
      }
    }

  **     2. The table is not a view and the column name identified an 
  **        explicitly declared column. Copy meta information from *pCol.
  */ 
  if( pCol ){
    zDataType = pCol->zType;
    zCollSeq = pCol->zColl;
    notnull = pCol->notNull!=0;
    primarykey  = (pCol->colFlags & COLFLAG_PRIMKEY)!=0;
    autoinc = pTab->iPKey==iCol && (pTab->tabFlags & TF_Autoincrement)!=0;
  }else{
    zDataType = "INTEGER";
    primarykey = 1;
  }
  if( !zCollSeq ){
    zCollSeq = "BINARY";

           pCol->zType ? pCol->zType : "", 0);
        sqlite3VdbeAddOp2(v, OP_Integer, (pCol->notNull ? 1 : 0), 4);
        if( pCol->zDflt ){
          sqlite3VdbeAddOp4(v, OP_String8, 0, 5, 0, (char*)pCol->zDflt, 0);
        }else{
          sqlite3VdbeAddOp2(v, OP_Null, 0, 5);
        }
        sqlite3VdbeAddOp2(v, OP_Integer,
                            (pCol->colFlags&COLFLAG_PRIMKEY)!=0, 6);
        sqlite3VdbeAddOp2(v, OP_ResultRow, 1, 6);
      }
    }
  }else

  if( sqlite3StrICmp(zLeft, "index_info")==0 && zRight ){
    Index *pIdx;

*/
struct Column {
  char *zName;     /* Name of this column */
  Expr *pDflt;     /* Default value of this column */
  char *zDflt;     /* Original text of the default value */
  char *zType;     /* Data type for this column */
  char *zColl;     /* Collating sequence.  If NULL, use the default */
  u8 notNull;      /* An OE_ code for handling a NOT NULL constraint */

  char affinity;   /* One of the SQLITE_AFF_... values */



  u16 colFlags;    /* Boolean properties.  See COLFLAG_ defines below */
};

/* Allowed values for Column.colFlags:
*/
#define COLFLAG_PRIMKEY  0x0001    /* Column is part of the primary key */
#define COLFLAG_HIDDEN   0x0002    /* A hidden column in a virtual table */

/*
** A "Collating Sequence" is defined by an instance of the following
** structure. Conceptually, a collating sequence consists of a name and
** a comparison routine that defines the order of that sequence.
**
** There may two separate implementations of the collation function, one
** that processes text in UTF-8 encoding (CollSeq.xCmp) and another that

/*
** Test to see whether or not a table is a virtual table.  This is
** done as a macro so that it will be optimized out when virtual
** table support is omitted from the build.
*/
#ifndef SQLITE_OMIT_VIRTUALTABLE
#  define IsVirtual(X)      (((X)->tabFlags & TF_Virtual)!=0)
#  define IsHiddenColumn(X) (((X)->colFlags & COLFLAG_HIDDEN)!=0)
#else
#  define IsVirtual(X)      0
#  define IsHiddenColumn(X) 0
#endif

/*
** Each foreign key constraint is an instance of the following structure.

      sqlite3VtabUnlock(pVTable);
      rc = SQLITE_ERROR;
    }else{
      int iCol;
      /* If everything went according to plan, link the new VTable structure
      ** into the linked list headed by pTab->pVTable. Then loop through the 
      ** columns of the table to see if any of them contain the token "hidden".
      ** If so, set the Column COLFLAG_HIDDEN flag and remove the token from
      ** the type string.  */
      pVTable->pNext = pTab->pVTable;
      pTab->pVTable = pVTable;

      for(iCol=0; iCol<pTab->nCol; iCol++){
        char *zType = pTab->aCol[iCol].zType;
        int nType;

          for(j=i; (j+nDel)<=nType; j++){
            zType[j] = zType[j+nDel];
          }
          if( zType[i]=='\0' && i>0 ){
            assert(zType[i-1]==' ');
            zType[i-1] = '\0';
          }
          pTab->aCol[iCol].colFlags |= COLFLAG_HIDDEN;
        }
      }
    }
  }

  sqlite3DbFree(db, zModuleName);
  return rc;