MySQL GROUP by name group to the maximum value of one, do not understand AH seek doubts. Solution Ideas

Source: Internet
Author: User
MySQL GROUP by name Group to get the most value one, do not understand Ah, ask for doubts.
Select A.* from Test a where 1 > (select COUNT (*) from test where name = A.name and val > A.val)
SQL statement, the field that displays the largest Val value by name group
Issue: SELECT COUNT (*) from test where name = A.name and val > a.val subquery is not a numeric value detected? The SQL statement doesn't have to be.
Select A.* from Test a where 1 >1? But this logic is obviously wrong, what is the right logic? How are the outer and inner layers compared? It's not enough to understand the IQ.
------to solve the idea----------------------
When the Val maximum is obtained, COUNT (*) is 0, 1>0 is not exactly satisfied
------to solve the idea----------------------
When the a.val is the maximum value
Val > A.val not set, (SELECT COUNT (*) from test where name = A.name and val > A.val) return 0 (no qualifying record)
1 > (select COUNT (*) from test where name = A.name and val > A.val)
Established, the record was elected

You already know, but you didn't get around bend.
Select A.* from Test a where 1 > Count
Count is the number of records that are greater than a.val, and only conut equals 0 when it does not exist. Expression 1 > 0 established
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