SQLite Query使用嵌套的SELECT

Question

I'm trying to select cpu_time from the db, but the time must correspond with a few other criteria - ie build_version, test_letter, design_index, multi_thread, and test_index

What I thought would work was (the inner SELECT DISTINCT statement works on its own):

set query [db eval \
    {SELECT DISTINCT cpu_time WHERE cpu_time IN 
            (SELECT DISTINCT mgc_version, test_type_letter, design_index, 
                             test_index, cpu_time, multi_thread 
                    FROM TestExecutions WHERE test_type_letter
                    BETWEEN $testletter AND $testletter)}]

***Note - this is giving me a "no such column: cpu_time" error

where my first SELECT would pull all items from a distinct return. Then, from each return, I wanted to ONLY use the cpu_time, for each type of $testletter.

This is for generating CSV files that only have the cpu_time. Is it obvious what I'm getting wrong?

Thank you!

Answer 1

You should always use WHERE xxx IN (SELECT xxx FROM ...) , instead of selecting multiple items in the inner select. You can add those in the outer select though, for example:

SELECT DISTINCT 
    mgc_version, 
    test_type_letter, 
    design_index, 
    test_index, 
    cpu_time, 
    multi_thread 
FROM TestExecutions
WHERE cpu_time IN 
(
    SELECT DISTINCT cpu_time 
    FROM TestExecutions 
    WHERE test_type_letter BETWEEN $testletter AND $testletter
)