Jak se interpretuje SQL s rekurzivním příkazem?

Žádná "rekurze" se zde nekoná a myslím si, že právě zde máte zmatek.

Z dokumentace PostgreSQL:http://www.postgresql.org/docs/9.4/static/queries-with.html

Note: Strictly speaking, this process is iteration not recursion, 
but RECURSIVE is the terminology chosen by the SQL standards committee.

Abychom parafrázovali tuto větu, WITH RECURSIVE lze zobrazit jako jednoduchý WHILE smyčka.

WITH RECURSIVE t(n) AS (
  VALUES (1)
  UNION ALL
  SELECT n+1 FROM t WHERE n < 100
)
SELECT * FROM t;

Zde je nějaký na míru vyrobený pseudokód, který tento proces podrobně vysvětluje

# Step 1: initialisation
LET cte_result = EMPTY
LET working_table = VALUES (1)
LET intermediate_table = EMPTY

# Step 2: result initialisation, merge initialisation into cte_result
cte_result = cte_result UNION working_table

# Step 3: iteration test
WHILE (working_table is not empty) DO
    # Step 4: iteration select, we substitute the self-reference with working_table
    intermediate_table = SELECT n+1 FROM working_table WHERE n < 100

    # Step 5: iteration merge, merge the iteration result into cte_result
    cte_result = cte_result UNION intermediate_table

    # Step 6: iteration end, prepare for next iteration
    working_table = intermediate_table
    intermediate_table = EMPTY
END WHILE

# Step 7: return
RETURN cte_result

A pomocí příkladu

# Step 1: initialisation
cte_result: EMPTY    | working_table: 1        | intermediate_table: EMPTY

# Step 2: result initialisation
cte_result: 1        | working_table: 1        | intermediate_table: EMPTY

# Step 3: iteration test
count(working_table) = 1 # OK
# Step 4: iteration select
cte_result: 1             | working_table: 1        | intermediate_table: 2
# Step 5: iteration merge
cte_result: 1, 2          | working_table: 1        | intermediate_table: 2
# Step 6: iteration end
cte_result: 1, 2          | working_table: 2        | intermediate_table: EMPTY

# Step 3: iteration test
count(working_table) = 1 # OK
# Step 4: iteration select
cte_result: 1, 2         | working_table: 2        | intermediate_table: 3
# Step 5: iteration merge
cte_result: 1, 2, 3      | working_table: 2        | intermediate_table: 3
# Step 6: iteration end
cte_result: 1, 2, 3      | working_table: 3        | intermediate_table: EMPTY

# … 97 more iterations and you get this state
cte_result: 1, 2, …, 100  | working_table: 100       | intermediate_table: EMPTY

# Step 3: iteration test
count(working_table) = 1 # OK
# Step 4: iteration select, the iteration query does not return any rows due to the WHERE clause
cte_result: 1, 2, …, 100  | working_table: 100       | intermediate_table: EMPTY
# Step 5: iteration merge, nothing is merged into the cte_result
cte_result: 1, 2, …, 100  | working_table: 100       | intermediate_table: EMPTY
# Step 6: iteration end
cte_result: 1, 2, …, 100  | working_table: EMPTY | intermediate_table: EMPTY

# Step 3: iteration test
count(working_table) = 0 # STOP

# Step 7: return
cte_result: 1, 2, …, 100

Takže výsledkem CTE jsou všechna čísla od 1 do 100.