MySQL中的SQL查询包含数学比较

Question

I need to have a SQL that finds values from table B using (randomize) values on table A in comparative manner. Table A values has been produces in randomize manner. Table B values have been order in a way of cumulative distribution function. What is needed is that SQL will get the first row from table B which satisfy the criteria.

Table A:
+----+-------+
| ID | value |
+----+-------+
|  1 | 0.1234|
|  2 | 0.8923|
|  3 | 0.5221|
+----+-------+

Table B:
+----+-------+------+
| ID | value | name | 
+----+-------+------+
|  1 | 0.2000| Alpha|
|  2 | 0.5000| Beta |
|  3 | 0.7500| Gamma|
|  4 | 1.0000| Delta|
+----+-------+------+

Result should be:
+----+-------+------+
| ID | value | name |
+----+-------+------+
|  1 | 0.1234| Alpha|
|  2 | 0.8923| Delta|
|  3 | 0.5221| Gamma|
+----+-------+------+

Value 0.1234 is smaller than all the values of B, but Alpha has smallest value.

Value 0.8923 is smaller than 1.000 --> Delta.

Value 0.5221 is smaller than both 0.7500 and 1.000 but 0.7500 is smallest --> Gamma.

This query works only if table A has one value:

select value, name
from B
where (select value from A) < value;

Any ideas how to get this work with full table A?

Answer 1

You can use subquery to get the data you need:

SELECT a.ID, a.value, 
    (SELECT b.name FROM TableB b WHERE a.value < b.value ORDER BY b.ID ASC LIMIT 1) as name
FROM TableA a

In this case for each row in table A you find the first record in table B, that has larger number in column value . Depending on your requirements the operator < might beed to be updated to <= - it depends on your requirements