SQLite

  SrcList *pSelectSrc = NULL;  /* SELECT rowid FROM x ... (dup of pSrc) */
  Select *pSelect = NULL;      /* Complete SELECT tree */

  /* Check that there isn't an ORDER BY without a LIMIT clause.
  */
  if( pOrderBy && (pLimit == 0) ) {
    sqlite3ErrorMsg(pParse, "ORDER BY without LIMIT on %s", zStmtType);
    goto limit_where_cleanup_2;
  }

  /* We only need to generate a select expression if there
  ** is a limit/offset term to enforce.
  */
  if( pLimit == 0 ) {
    /* if pLimit is null, pOffset will always be null as well. */

  ** becomes:
  **   DELETE FROM table_a WHERE rowid IN ( 
  **     SELECT rowid FROM table_a WHERE col1=1 ORDER BY col2 LIMIT 1 OFFSET 1
  **   );
  */

  pSelectRowid = sqlite3PExpr(pParse, TK_ROW, 0, 0, 0);
  if( pSelectRowid == 0 ) goto limit_where_cleanup_2;
  pEList = sqlite3ExprListAppend(pParse, 0, pSelectRowid);
  if( pEList == 0 ) goto limit_where_cleanup_2;

  /* duplicate the FROM clause as it is needed by both the DELETE/UPDATE tree
  ** and the SELECT subtree. */
  pSelectSrc = sqlite3SrcListDup(pParse->db, pSrc, 0);
  if( pSelectSrc == 0 ) {
    sqlite3ExprListDelete(pParse->db, pEList);
    goto limit_where_cleanup_2;
  }

  /* generate the SELECT expression tree. */
  pSelect = sqlite3SelectNew(pParse,pEList,pSelectSrc,pWhere,0,0,
                             pOrderBy,0,pLimit,pOffset);
  if( pSelect == 0 ) return 0;

  /* now generate the new WHERE rowid IN clause for the DELETE/UDPATE */
  pWhereRowid = sqlite3PExpr(pParse, TK_ROW, 0, 0, 0);
  if( pWhereRowid == 0 ) goto limit_where_cleanup_1;
  pInClause = sqlite3PExpr(pParse, TK_IN, pWhereRowid, 0, 0);
  if( pInClause == 0 ) goto limit_where_cleanup_1;

  pInClause->x.pSelect = pSelect;
  pInClause->flags |= EP_xIsSelect;
  sqlite3ExprSetHeightAndFlags(pParse, pInClause);
  return pInClause;

  /* something went wrong. clean up anything allocated. */
limit_where_cleanup_1:
  sqlite3SelectDelete(pParse->db, pSelect);
  return 0;

limit_where_cleanup_2:
  sqlite3ExprDelete(pParse->db, pWhere);
  sqlite3ExprListDelete(pParse->db, pOrderBy);
  sqlite3ExprDelete(pParse->db, pLimit);
  sqlite3ExprDelete(pParse->db, pOffset);
  return 0;
}
#endif /* defined(SQLITE_ENABLE_UPDATE_DELETE_LIMIT) */

    sqlite3ExprAttachSubtrees(pParse->db, p, pLeft, pRight);
  }
  if( p ) {
    sqlite3ExprCheckHeight(pParse, p->nHeight);
  }
  return p;
}

















/*
** If the expression is always either TRUE or FALSE (respectively),
** then return 1.  If one cannot determine the truth value of the
** expression at compile-time return 0.
**
** This is an optimization.  If is OK to return 0 here even if

      exprNot(pParse, N, &A);
    }
    A.zEnd = &E.z[E.n];
  }
  expr(A) ::= LP(B) select(X) RP(E). {
    spanSet(&A,&B,&E); /*A-overwrites-B*/
    A.pExpr = sqlite3PExpr(pParse, TK_SELECT, 0, 0, 0);
    if( A.pExpr ){
      A.pExpr->x.pSelect = X;
      ExprSetProperty(A.pExpr, EP_xIsSelect|EP_Subquery);
      sqlite3ExprSetHeightAndFlags(pParse, A.pExpr);
    }else{
      sqlite3SelectDelete(pParse->db, X);
    }
  }
  expr(A) ::= expr(A) in_op(N) LP select(Y) RP(E).  [IN] {
    A.pExpr = sqlite3PExpr(pParse, TK_IN, A.pExpr, 0, 0);
    if( A.pExpr ){
      A.pExpr->x.pSelect = Y;
      ExprSetProperty(A.pExpr, EP_xIsSelect|EP_Subquery);
      sqlite3ExprSetHeightAndFlags(pParse, A.pExpr);
    }else{
      sqlite3SelectDelete(pParse->db, Y);
    }
    exprNot(pParse, N, &A);
    A.zEnd = &E.z[E.n];
  }
  expr(A) ::= expr(A) in_op(N) nm(Y) dbnm(Z). [IN] {
    SrcList *pSrc = sqlite3SrcListAppend(pParse->db, 0,&Y,&Z);

    A.pExpr = sqlite3PExpr(pParse, TK_IN, A.pExpr, 0, 0);
    if( A.pExpr ){
      A.pExpr->x.pSelect = sqlite3SelectNew(pParse, 0,pSrc,0,0,0,0,0,0,0);
      ExprSetProperty(A.pExpr, EP_xIsSelect|EP_Subquery);
      sqlite3ExprSetHeightAndFlags(pParse, A.pExpr);
    }else{
      sqlite3SrcListDelete(pParse->db, pSrc);
    }
    exprNot(pParse, N, &A);
    A.zEnd = Z.z ? &Z.z[Z.n] : &Y.z[Y.n];
  }
  expr(A) ::= EXISTS(B) LP select(Y) RP(E). {
    Expr *p;
    spanSet(&A,&B,&E); /*A-overwrites-B*/
    p = A.pExpr = sqlite3PExpr(pParse, TK_EXISTS, 0, 0, 0);
    if( p ){
      p->x.pSelect = Y;
      ExprSetProperty(p, EP_xIsSelect|EP_Subquery);
      sqlite3ExprSetHeightAndFlags(pParse, p);
    }else{
      sqlite3SelectDelete(pParse->db, Y);
    }
  }
%endif SQLITE_OMIT_SUBQUERY

/* CASE expressions */
expr(A) ::= CASE(C) case_operand(X) case_exprlist(Y) case_else(Z) END(E). {
  spanSet(&A,&C,&E);  /*A-overwrites-C*/
  A.pExpr = sqlite3PExpr(pParse, TK_CASE, X, 0, 0);

#ifdef SQLITE_DEBUG
int sqlite3NoTempsInRange(Parse*,int,int);
#endif
Expr *sqlite3ExprAlloc(sqlite3*,int,const Token*,int);
Expr *sqlite3Expr(sqlite3*,int,const char*);
void sqlite3ExprAttachSubtrees(sqlite3*,Expr*,Expr*,Expr*);
Expr *sqlite3PExpr(Parse*, int, Expr*, Expr*, const Token*);

Expr *sqlite3ExprAnd(sqlite3*,Expr*, Expr*);
Expr *sqlite3ExprFunction(Parse*,ExprList*, Token*);
void sqlite3ExprAssignVarNumber(Parse*, Expr*);
void sqlite3ExprDelete(sqlite3*, Expr*);
ExprList *sqlite3ExprListAppend(Parse*,ExprList*,Expr*);
void sqlite3ExprListSetSortOrder(ExprList*,int);
void sqlite3ExprListSetName(Parse*,ExprList*,Token*,int);