Using a column in a CTE that does not exist in another table - sql

Question

I am new to writing recursive queries and I am trying to write my first one. I am trying to determine levels of a corporate hierarchy and have the result table include two columns- the consultant ID and the level that has been determined by the recursive query. In the CTE, I can't figure out how to reference "level" since it is a column that doesn't yet exist in a table. What am I doing wrong?
WITH consultantsandlevels
(c."ConsultantDisplayID",
consultantsandlevels."level"
)
AS
(
SELECT c."ConsultantDisplayID",
0
FROM flight_export_consultant AS c
WHERE c."ParentPersonDisplayID" IS NULL
UNION all
SELECT c."ConsultantDisplayID",
c."ParentPersonDisplayID",
consultantsandlevels."level" + 1
FROM flight_export_consultant
JOIN consultantsandlevels ON c."ParentPersonDisplayID" = consultantsandlevels."ConsultantDisplayID"
)
SELECT *
FROM consultantsandlevels;

Answer 1

I think you want:
WITH RECURSIVE consultantsandlevels(ConsultantDisplayID, level) AS (
SELECT "ConsultantDisplayID", 0
FROM flight_export_consultant
WHERE "ParentPersonDisplayID" IS NULL
UNION ALL
SELECT fec."ConsultantDisplayID", cal.level + 1
FROM flight_export_consultant fec
INNER JOIN consultantsandlevels cal
ON fec."ParentPersonDisplayID" = cal.ConsultantDisplayID
)
SELECT * FROM consultantsandlevels;
Rationale:
The WITH clause must start with keyword RECURSIVE
The declaration of the comon-table-expression just enumerates the column names (no table prefix should appear there).
The level is initially set to 0, and you can then increment it at each iteration by refering to corresponding common-table-expression column.
Queries on both sides of UNION ALL must return the same count of columns (that correspond to the declaration of the cte) with corresponding datatypes.