Question

I’m writing a SQL embedded in C program with tables below:

table index:id, xx

table a:id, year, yy

table b:id, year, zz

table c:id, year, vv

id in a,b,c belong to id in index

Then how to select all the id order by year?

Answer 1

You question is not very clear about what you are after. Superficially, one possible answer might be:

SELECT i.id, i.xx, a.year, a.yy
  FROM index AS i
  JOIN a ON i.id = a.id
UNION
SELECT i.id, i.xx, b.year, b.zz
  FROM index AS i
  JOIN b ON i.id = b.id
UNION
SELECT i.id, i.xx, c.year, c.vv
  FROM index AS i
  JOIN c ON i.id = c.id
ORDER BY year, id;

If all of tables A, B, and C join to a single row in Index, then there are alternative queries (using more joins, possibly some of them being LEFT OUTER JOIN). If the columns represented by yy, zz and vv are not compatible, then you need to specify what to do with them (or simply leave them out of the query).