Well, that's not how SQL works, but, in the interest of fun....
Are the tables ALWAYS the same layout? (i.e. have the exact same columns?)
If that is the case, then one can do something like this:
```
WITH normalized(age, weight, percentile) AS (
SELECT age, c10, 10 FROM centiles UNION ALL
SELECT age, c25, 25 FROM centiles UNION ALL
SELECT age, c50, 50 FROM centiles UNION ALL
SELECT age, c75, 75 FROM centiles UNION ALL
SELECT age, c90, 90 FROM centiles
)
SELECT *
FROM normalized
;
-- And to get the specific percentile for Age 3 at weight 9 - simply chenge the end query to
SELECT percentile
FROM normalized
WHERE age = 3 AND weight = 9
;
EDIT: I should add that the table "centiles" being used is constructed from the OP's given layout - resulting in:
CREATE TABLE centiles(age, c10, c25, c50, c75, c90);
INSERT INTO centiles VALUES
( 1, 5, 6, 7, 8, 9)
,( 2, 6, 7, 8, 9, 10)
,( 3, 7, 8, 9, 10, 11)
;
```
This will work for any size table and can be adjusted to suit more columns.