在键名是列名的键上连接两个表

Question

I'm trying to join two tables where the first tables contains ID's and measure.

Skey | ID | Measure
1    | A1 | 12
2    | A1 | 34
3    | A2 | Green
4    | A4 | 0.00005

The second tables contains the table name ID and ID data type.

ID | DataType
A1 | int
A2 | character
A4 | decimal

I want to do a join using these tables which will result in the following table

Skey | ID | int | character | decimal
1    | A1 | 12  |    NA     |   NA
2    | A1 | 34  |    NA     |   NA
3    | A2 | NA  |   Green   |   NA
4    | A4 | NA  |    NA     | 0.00005

Can this be done? If yes, need to understand the logic and the way to accomplish it.

Answer 1

What fun! You can join and use case :

select t1.skey, t1.id,
       (case when t2.type = 'int' then cast(t2.measure as int) end) as int_col,
       (case when t2.type = 'character' then cast(t2.measure as varchar(255)) end) as int_col,
       (case when t2.type = 'int' then cast(t2.measure as decimal) end) as decimal_col
from table1 t1 join
     table2 t2
     on t1.id = t2.id;

A couple of caveats:

• You might want a different length, character set, or collation for the string column. How you do that depends on the database.
• Some databases will convert the string '0.0005' to 0.0005 , some to 0 . You might need to include precision and scale for the actual conversion.