Help with re-writing this query

Question

Dear experts;
create table t2
  ID varchar2(1000),
  name varchar2(1000),
   place varchar2(1000)
create table mappingt2
  grades varchar2(1000)
  individual varchar2(1000)
insert into t2 values ('James', 'John', 'newyork');
insert into t2 values ('Linda', 'James', 'London');
insert into t2 values ('Alex', 'kim', 'Mexico');
insert into t2 values ('karen', 'Jack', 'Tunis');
insert into t2 values ('CC', 'Jack', 'Peru');
insert into t2 values ('Linda', 'James', 'Germany');
insert into mappingt2 values ('A', 'James');
insert into mappingt2 values ('C', 'Kim');
insert into mappingt2 values ('C', 'Linda');
insert into mappingt2 values ('B', 'CC');I have the following query below
SELECT (select grades from mappingt2 t
   where t.individual =  pt.ID) as current_grade
      ,(select grades from mappingt2 ty
   where ty.individual =  pt.name) alt_grade
      ,pt.place
  FROM t2 ptI was just wondering whether this query can be better written. All help is appreciated. Thank you

Answer 1

user13328581 wrote:
Hi Frank, Tom Kyte claims sub scalar queries is usually betterHe didn't say usually he said if you want the first row faster
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if your goal is to optimize your query for initial response time, you may want to use the former query, with the scalar subquery, because Oracle Database would have to get just the first row from DEPT, run the scalar subquery (select count...) against EMP to get the count, and then return it. The process for returning that first row would be very fast.
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The corollary to this that was not explicitly mentioned in the article that I can see is that this probably comes at the expense of the time taken to return all the rows which can then take longer.