基于查询的UPDATE SQL表

Question

I have a table called students with 1000 students in. I have a query which tells me which of those students has free tuition. In the stduents table I have a field called FreeTuition and I want to populate/update that field with the results of the query. Do I need to use some kind of loop?

The students table has StuCode which is unique, the query returns StuCode of all the students with free tuition. This is how I want it to look:

| StuCode | FreeTuition |
-------------------------
| S12345  | Yes         |
| S12346  | No          |
-------------------------

Answer 1

Not at all. Something like this:

with yourquery as (
      <your query here>
     )
update s
    set FreeTuition = (case when yq. StuCode is not null then 'Y' else 'N' end)
    from students s left join
         yourquery yq
         on s. StuCode = yq. StuCode;

Note: This sets the value for all students, yes or no. You can change the left join to just join to set the value only for students returned by the subquery.