mysql：将多行合并为一个

Question

I have two tables: state_current and state_snapshots . state_current contains exactly 4 rows, the current values for 4 different keys:

+-----+-------+
| key | value |
+-----+-------+
| A   |     1 |
| B   |     2 |
| C   |     3 |
| D   |     4 |
+-----+-------+

Now, I want to add a row to state_snapshots that contains the values of each key in a seperate column:

+---+---+---+---+
| A | B | C | D |
+---+---+---+---+
| 1 | 2 | 3 | 4 |
| 1 | 2 | 3 | 5 |
| 1 | 2 | 4 | 5 |
 ...
+---+---+---+---+

Of course, the keys never change in state_current , only the values. What mySQL-query will create a row with the value of A in state_current in the first column, the value of B in state_current in the second and so on?

I'm new to mySQL, so thanks in advance for any help!

Answer 1

The simplest answer I can think about is:

insert into state_snapshots(a,b,c,d)
   values ( (select value from state_current where key='A'),
            (select value from state_current where key='B'),
            (select value from state_current where key='C'),
            (select value from state_current where key='D')
          );