SQL to re-display the first piece of data to display a single piece of data

Requirement Description: To display any data, first or last, according to a field or several fields.

Data styles such as:

Try to resolve:

-- Count (*) method (only shows the number of bars is 1, more than 1 filter all) Select *  from where inch (Selectfromgroupby hasCount(id)=  1)

The above method will show only 1 records, but the repetition does not keep one of them, also filtered out.

So, we need to change a bit and provide three solutions:

First, by the row_number by the repeating field grouping sorts, then displays 1th, uses the AB table way:

--Select  A.* from T4 A, (Selectthrough  order by as from T4) bwhere=  and B.nid=1

Second, the same method, by Row_number by repeating the field of grouping sorting, and then display 1th. But using sub-query mode:

Select A.*fromselect row_number ()throughorder   by as Nid,* from T4  ) awhere a.nid=  1

Third, by grouping to take the minimum or maximum value for resolution.

Select *  from where inch (Selectminfromgroup by self-coding)

This is the simplest approach, but the ID requirement must be a number that can be calculated for min or max. If there is no pure digital ID, you can use Row_number to establish NID first, then Min.

Select Row_number ()throughorder by as Nid,*from T4

The above three kinds of schemes have the same effect.

SQL to re-display the first data to display a single piece of data