如何 select 列名来自 SQL 中另一个表的值？

Question

I have two tables table B has some column names of table A which are divide into different groups, now I want to select data from A which belong to a certain group in B, how to write such query?

To illustrate

Table A looks like this

|key|c1|c2|c3|c4|
|p1 |11|21|23|23|
|p2 |10|22|33|21|
|p3 |20|32|53|90|
|p4 |20|42|43|98|

Table B looks like this

|cloumnName|Group|
|c1|g1|
|c2|g1|
|c3|g2|
|c4|g2|

I know to select c1 c2 from B is

select columnName from B where Group='g1'

However how can I select data from table A where key='p1' and contains the columns(c1, c2) from the result above? like (p1, 11,21)

Answer 1

you can do pivot and join

 select b.*,a.* from

(select max(case when cloumnName='c1' then [group] end) as c1,
       max(case when cloumnName='c2' then [group] end) as c2,
       max(case when cloumnName='c3' then [group] end) as c3,
      max(case when cloumnName='c4' then [group] end) as c4
     from tableB
) b join tableA a on b.c1=a.c1 and b.c2=a.c2 and b.c3=a.c3 and b.c4=a.c4