SQLite

    case TK_AS: {
      inReg = sqlite3ExprCodeTarget(pParse, pExpr->pLeft, target);
      break;
    }
#ifndef SQLITE_OMIT_CAST
    case TK_CAST: {
      /* Expressions of the form:   CAST(pLeft AS token) */
      int aff, to_op;
      inReg = sqlite3ExprCodeTarget(pParse, pExpr->pLeft, target);
      assert( !ExprHasProperty(pExpr, EP_IntValue) );
      aff = sqlite3AffinityType(pExpr->u.zToken, 0);
      to_op = aff - SQLITE_AFF_TEXT + OP_ToText;
      assert( to_op==OP_ToText    || aff!=SQLITE_AFF_TEXT    );
      assert( to_op==OP_ToBlob    || aff!=SQLITE_AFF_NONE    );
      assert( to_op==OP_ToNumeric || aff!=SQLITE_AFF_NUMERIC );
      assert( to_op==OP_ToInt     || aff!=SQLITE_AFF_INTEGER );
      assert( to_op==OP_ToReal    || aff!=SQLITE_AFF_REAL    );
      testcase( to_op==OP_ToText );
      testcase( to_op==OP_ToBlob );
      testcase( to_op==OP_ToNumeric );
      testcase( to_op==OP_ToInt );
      testcase( to_op==OP_ToReal );
      if( inReg!=target ){
        sqlite3VdbeAddOp2(v, OP_SCopy, inReg, target);
        inReg = target;
      }
      sqlite3VdbeAddOp1(v, to_op, inReg);
      sqlite3VdbeAddOp2(v, OP_Cast, target,
                        sqlite3AffinityType(pExpr->u.zToken, 0));
      testcase( usedAsColumnCache(pParse, inReg, inReg) );
      sqlite3ExprCacheAffinityChange(pParse, inReg, 1);
      break;
    }
#endif /* SQLITE_OMIT_CAST */
    case TK_LT:
    case TK_LE:

    sqlite3VdbeMemRealify(pIn1);
  }
  break;
}
#endif

#ifndef SQLITE_OMIT_CAST
/* Opcode: ToText P1 * * * *
/* Opcode: Cast P1 P2 * * *
**
** Force the value in register P1 to be text.
** Force the value in register P1 to be the type defined by P2.
** If the value is numeric, convert it to a string using the
** equivalent of sprintf().  Blob values are unchanged and
** are afterwards simply interpreted as text.
**
** 
** A NULL value is not changed by this routine.  It remains NULL.
*/
case OP_ToText: {                  /* same as TK_TO_TEXT, in1 */
  pIn1 = &aMem[pOp->p1];
  memAboutToChange(p, pIn1);
  if( pIn1->flags & MEM_Null ) break;
  assert( MEM_Str==(MEM_Blob>>3) );
  pIn1->flags |= (pIn1->flags&MEM_Blob)>>3;
  applyAffinity(pIn1, SQLITE_AFF_TEXT, encoding);
  rc = ExpandBlob(pIn1);
  assert( pIn1->flags & MEM_Str || db->mallocFailed );
  pIn1->flags &= ~(MEM_Int|MEM_Real|MEM_Blob|MEM_Zero);
  UPDATE_MAX_BLOBSIZE(pIn1);
  break;
}

/* Opcode: ToBlob P1 * * * *
**
** <ul>
** Force the value in register P1 to be a BLOB.
** If the value is numeric, convert it to a string first.
** Strings are simply reinterpreted as blobs with no change
** to the underlying data.
**
** <li value="97"> TEXT
** A NULL value is not changed by this routine.  It remains NULL.
*/
case OP_ToBlob: {                  /* same as TK_TO_BLOB, in1 */
  pIn1 = &aMem[pOp->p1];
  if( pIn1->flags & MEM_Null ) break;
  if( (pIn1->flags & MEM_Blob)==0 ){
    applyAffinity(pIn1, SQLITE_AFF_TEXT, encoding);
    assert( pIn1->flags & MEM_Str || db->mallocFailed );
    MemSetTypeFlag(pIn1, MEM_Blob);
  }else{
    pIn1->flags &= ~(MEM_TypeMask&~MEM_Blob);
  }
  UPDATE_MAX_BLOBSIZE(pIn1);
** <li value="98"> BLOB
  break;
}

** <li value="99"> NUMERIC
/* Opcode: ToNumeric P1 * * * *
**
** Force the value in register P1 to be numeric (either an
** <li value="100"> INTEGER
** <li value="101"> REAL
** integer or a floating-point number.)
** If the value is text or blob, try to convert it to an using the
** equivalent of atoi() or atof() and store 0 if no such conversion 
** is possible.
**
** </ul>
** A NULL value is not changed by this routine.  It remains NULL.
*/
case OP_ToNumeric: {                  /* same as TK_TO_NUMERIC, in1 */
  pIn1 = &aMem[pOp->p1];
  sqlite3VdbeMemNumerify(pIn1);
  break;
}
#endif /* SQLITE_OMIT_CAST */

/* Opcode: ToInt P1 * * * *
**
** Force the value in register P1 to be an integer.  If
** The value is currently a real number, drop its fractional part.
** If the value is text or blob, try to convert it to an integer using the
** equivalent of atoi() and store 0 if no such conversion is possible.
**
** A NULL value is not changed by this routine.  It remains NULL.
*/
case OP_ToInt: {                  /* same as TK_TO_INT, in1 */
case OP_Cast: {                  /* in1 */
  pIn1 = &aMem[pOp->p1];
  if( (pIn1->flags & MEM_Null)==0 ){
    sqlite3VdbeMemIntegerify(pIn1);
  }
  break;
}

#if !defined(SQLITE_OMIT_CAST) && !defined(SQLITE_OMIT_FLOATING_POINT)
/* Opcode: ToReal P1 * * * *
**
** Force the value in register P1 to be a floating point number.
** If The value is currently an integer, convert it.
** If the value is text or blob, try to convert it to an integer using the
** equivalent of atoi() and store 0.0 if no such conversion is possible.
**
** A NULL value is not changed by this routine.  It remains NULL.
*/
case OP_ToReal: {                  /* same as TK_TO_REAL, in1 */
  pIn1 = &aMem[pOp->p1];
  memAboutToChange(p, pIn1);
  if( (pIn1->flags & MEM_Null)==0 ){
    sqlite3VdbeMemRealify(pIn1);
  rc = ExpandBlob(pIn1);
  sqlite3VdbeMemCast(pIn1, pOp->p2, encoding);
  }
  UPDATE_MAX_BLOBSIZE(pIn1);
  break;
}
#endif /* !defined(SQLITE_OMIT_CAST) && !defined(SQLITE_OMIT_FLOATING_POINT) */
#endif /* SQLITE_OMIT_CAST */

/* Opcode: Lt P1 P2 P3 P4 P5
** Synopsis: if r[P1]<r[P3] goto P2
**
** Compare the values in register P1 and P3.  If reg(P3)<reg(P1) then
** jump to address P2.  
**

int sqlite3VdbeMemStringify(Mem*, u8, u8);
i64 sqlite3VdbeIntValue(Mem*);
int sqlite3VdbeMemIntegerify(Mem*);
double sqlite3VdbeRealValue(Mem*);
void sqlite3VdbeIntegerAffinity(Mem*);
int sqlite3VdbeMemRealify(Mem*);
int sqlite3VdbeMemNumerify(Mem*);
void sqlite3VdbeMemCast(Mem*,u8,u8);
int sqlite3VdbeMemFromBtree(BtCursor*,u32,u32,int,Mem*);
void sqlite3VdbeMemRelease(Mem *p);
void sqlite3VdbeMemReleaseExternal(Mem *p);
#define VdbeMemDynamic(X)  \
  (((X)->flags&(MEM_Agg|MEM_Dyn|MEM_RowSet|MEM_Frame))!=0)
#define VdbeMemReleaseExtern(X)  \
  if( VdbeMemDynamic(X) ) sqlite3VdbeMemReleaseExternal(X);

      sqlite3VdbeIntegerAffinity(pMem);
    }
  }
  assert( (pMem->flags & (MEM_Int|MEM_Real|MEM_Null))!=0 );
  pMem->flags &= ~(MEM_Str|MEM_Blob);
  return SQLITE_OK;
}

/*
** Cast the datatype of the value in pMem according to the affinity
** "aff".  Casting is different from applying affinity in that a cast
** is forced.  In other words, the value is converted into the desired
** affinity even if that results in loss of data.  This routine is
** used (for example) to implement the SQL "cast()" operator.
*/
void sqlite3VdbeMemCast(Mem *pMem, u8 aff, u8 encoding){
  if( pMem->flags & MEM_Null ) return;
  switch( aff ){
    case SQLITE_AFF_NONE: {   /* Really a cast to BLOB */
      if( (pMem->flags & MEM_Blob)==0 ){
        sqlite3ValueApplyAffinity(pMem, SQLITE_AFF_TEXT, encoding);
        assert( pMem->flags & MEM_Str || pMem->db->mallocFailed );
        MemSetTypeFlag(pMem, MEM_Blob);
      }else{
        pMem->flags &= ~(MEM_TypeMask&~MEM_Blob);
      }
      break;
    }
    case SQLITE_AFF_NUMERIC: {
      sqlite3VdbeMemNumerify(pMem);
      break;
    }
    case SQLITE_AFF_INTEGER: {
      sqlite3VdbeMemIntegerify(pMem);
      break;
    }
    case SQLITE_AFF_REAL: {
      sqlite3VdbeMemRealify(pMem);
      break;
    }
    default: {
      assert( aff==SQLITE_AFF_TEXT );
      assert( MEM_Str==(MEM_Blob>>3) );
      pMem->flags |= (pMem->flags&MEM_Blob)>>3;
      sqlite3ValueApplyAffinity(pMem, SQLITE_AFF_TEXT, encoding);
      assert( pMem->flags & MEM_Str || pMem->db->mallocFailed );
      pMem->flags &= ~(MEM_Int|MEM_Real|MEM_Blob|MEM_Zero);
      break;
    }
  }
}


/*
** Delete any previous value and set the value stored in *pMem to NULL.
*/
void sqlite3VdbeMemSetNull(Mem *pMem){
  if( pMem->flags & MEM_Frame ){
    VdbeFrame *pFrame = pMem->u.pFrame;

  const char *zNeg = "";
  int rc = SQLITE_OK;

  if( !pExpr ){
    *ppVal = 0;
    return SQLITE_OK;
  }
  op = pExpr->op;
  while( (op = pExpr->op)==TK_UPLUS ) pExpr = pExpr->pLeft;
  if( NEVER(op==TK_REGISTER) ) op = pExpr->op2;

  if( op==TK_CAST ){
    u8 aff = sqlite3AffinityType(pExpr->u.zToken,0);
    rc = valueFromExpr(db, pExpr->pLeft, enc, aff, ppVal, pCtx);
    if( rc==SQLITE_OK && *ppVal ){
      sqlite3VdbeMemCast(*ppVal, aff, SQLITE_UTF8);
      sqlite3ValueApplyAffinity(*ppVal, affinity, SQLITE_UTF8);
    }
    return rc;
  }

  /* Handle negative integers in a single step.  This is needed in the
  ** case when the value is -9223372036854775808.
  */
  if( op==TK_UMINUS
   && (pExpr->pLeft->op==TK_INTEGER || pExpr->pLeft->op==TK_FLOAT) ){
    pExpr = pExpr->pLeft;

do_test alter4-2.6 {
  catchsql {
    alter table t1 add column d DEFAULT CURRENT_TIME;
  }
} {1 {Cannot add a column with non-constant default}}
do_test alter4-2.7 {
  catchsql {
    alter table t1 add column d default (-+1);
    alter table t1 add column d default (-5+1);
  }
} {1 {Cannot add a column with non-constant default}}
do_test alter4-2.99 {
  execsql {
    DROP TABLE t1;
  }
} {}