什么是 select 的正确方法是列中的最大值而不是主键

Question

I have a table (report) consist of several records and one of them about int values (column) I am trying to get the highest number of the fall_value column the id only primary key, the table as following:

id (P)	fall_value	date
3	1.2	2021-01-29
4	1.5	2021-01-30
5	1.6	2021-01-30
6	1	2021-01-31
7	5	2021-01-31
8	1.5	2021-01-31
9	1.5	2021-01-31
10	14	2021-01-31
11	15	2021-01-31

expected result: 15

I have tried the following inquiry:

SELECT max(fall_value) from report;

I got an unexpected result: 5

and also I got a message saying:

Current selection does not contain a unique column. Grid edit, checkbox, Edit, Copy and Delete features are not available

Answer 1

It sounds like fall_value is a string, not a number, and the string "5" is indeed greater than the string "15".

Try converting to a number. A convenient way is to use implicit conversion:

SELECT max(fall_value + 0) 
FROM report;