SQL custom sorting

There was a demand for a while ago, and the sorting rules should be arranged according to the user's needs:

Example:

The database is Oracle, which sorts the class fields of table table_example. The class fields include A, B, C, and D.

The user requires that the data in table_example be ordered by class field values C, A, D, and B.

Method 1:

I started to think of a way to add a custom Field custom when selecting, when the class values are C, A, D, and B, the m values are 1, 2, 3, and 4.

When using case when, we can achieve this without adding custom fields:

Teble_exaple

Method 2:

Using Program-side control, the implementation logic is still complicated due to PB, without further research. The idea is as follows: (for reference only, not implemented .)

Dw _. setsort (class =, (class =,. sort

Method 3:

Use the decode function:

Table_example decode (class ,,,,,,,,)

The function with similar functions in sqlserver is charindex.

Method 3 is the most concise solution. I personally feel that in many cases, the functions implemented by SQL are more direct than those implemented by the program.