How to use MySQL group

Q: How can I filter repeated items using group by? Could you give me an example?

 

Answer:

Example AA Table a B 123 10 123 12 1234 11 1234 14 first, group is used to group data, not to filter duplicate items. Duplicate deletion statement distinct uses this. The Select distinct (a) from AA result is the select a, sum (B) from AA group by a sum used for grouping by a 123 group. The result is that the B 123 22 1234 25 Statement aims to set a as the target and needs to know the total number of items with the same name in column B. Select a, count (B) from AA group by a count indicates the sum of the number of rows. The result is a B 123 2 1234 2 Statement, which indicates the total number of rows of an item with the same name.