Teradata sql Analytics - derived a new column for partitioned clause

Question

I have a Book table, and i want to derived a new column word1 as below:

Book:

+-------+------+------+-------+
| name  | page | line | word  |
+-------+------+------+-------+
| Book1 | 1    | 1    | The   |
+-------+------+------+-------+
| Book1 | 1    | 2    | A     |
+-------+------+------+-------+
| Book1 | 1    | 3    | Time  |
+-------+------+------+-------+
| Book1 | 1    | 4    | A     |
+-------+------+------+-------+
| Book1 | 2    | 1    | An    |
+-------+------+------+-------+
| Book1 | 2    | 2    | Tom   |
+-------+------+------+-------+
| Book1 | 2    | 3    | A     |
+-------+------+------+-------+
| Book1 | 3    | 1    | A     |
+-------+------+------+-------+
| Book1 | 3    | 2    | Jack  |
+-------+------+------+-------+
| Book1 | 3    | 3    | A     |
+-------+------+------+-------+
| Book1 | 4    | 1    | Since |
+-------+------+------+-------+
| Book1 | 4    | 2    | They  |
+-------+------+------+-------+
| Book1 | 4    | 3    | Sam   |
+-------+------+------+-------+

Derived Word1 as
CASE
if any of the line for same page has 'The' then 'The'
if any of the line for same page has 'An' then 'An'
if any of the line for same page has 'A' then 'A'
ELSE
word at line 1

+-------+------+------+-------+-------+
| name  | page | line | word  | word1 |
+-------+------+------+-------+-------+
| Book1 | 1    | 1    | The   | The   |
+-------+------+------+-------+-------+
| Book1 | 1    | 2    | A     | The   |
+-------+------+------+-------+-------+
| Book1 | 1    | 3    | Time  | The   |
+-------+------+------+-------+-------+
| Book1 | 1    | 4    | A     | The   |
+-------+------+------+-------+-------+
| Book1 | 2    | 1    | An    | An    |
+-------+------+------+-------+-------+
| Book1 | 2    | 2    | Tom   | An    |
+-------+------+------+-------+-------+
| Book1 | 2    | 3    | A     | An    |
+-------+------+------+-------+-------+
| Book1 | 3    | 1    | A     | A     |
+-------+------+------+-------+-------+
| Book1 | 3    | 2    | Jack  | A     |
+-------+------+------+-------+-------+
| Book1 | 3    | 3    | A     | A     |
+-------+------+------+-------+-------+
| Book1 | 4    | 1    | Since | Since |
+-------+------+------+-------+-------+
| Book1 | 4    | 2    | They  | Since |
+-------+------+------+-------+-------+
| Book1 | 4    | 3    | Sam   | Since |
+-------+------+------+-------+-------+

Answer 1

Apply FIRST_VALUE and order by priority:

SELECT ...
   First_Value(word) 
   Over (PARTITION BY NAME, page
         ORDER BY 
            CASE word 
              WHEN 'The' THEN 1
              WHEN 'An'  THEN 2
              WHEN 'A'   THEN 3
              ELSE 99
            END, line)
FROM tab