在添加order by之前，您的条件已连接到where子句。现在order by位于sql变量中查询文本的末尾，稍后的连接将向order by（而不是where部分）添加内容，第一个内容以bk_title and bk_title ilike ...结束，这会导致错误。
给定一个searchterm='The Lord of The Rings'，它曾经是

SELECT bk_title, bk_author, genre_name, bk_pub_yr, bk_inv_count, bk_id
FROM books INNER JOIN genres on books.genre_id = genres.genre_id
WHERE NOT bk_delete_ind AND bk_title ILIKE '%The Lord of The Rings%'

现在它结束为：

SELECT bk_title, bk_author, genre_name, bk_pub_yr, bk_inv_count, bk_id
FROM books INNER JOIN genres on books.genre_id = genres.genre_id
WHERE NOT bk_delete_ind
ORDER BY bk_title AND bk_title ILIKE '%The Lord of The Rings%'; --invalid
         ^        ^   ^
         varchar  ^   (varchar ILIKE text) evaluates to boolean
                  ^   
                  "AND" requires a boolean to the left and right
                  it is now getting varchar on the left and boolean on the right

你可能想

SELECT bk_title, bk_author, genre_name, bk_pub_yr, bk_inv_count, bk_id
FROM books INNER JOIN genres on books.genre_id = genres.genre_id
WHERE NOT bk_delete_ind AND bk_title ILIKE '%The Lord of The Rings%' 
ORDER BY bk_title

从初始的sql变量值中删除order by，并在填写完where条件后添加它。

def updatebooks_allbooks_list_atoz(pathname, searchterm):
if pathname == '/' or '/books':
    
    sql = """ SELECT bk_title, bk_author, genre_name, bk_pub_yr, bk_inv_count, bk_id
            FROM books
                INNER JOIN genres on books.genre_id = genres.genre_id
            WHERE NOT bk_delete_ind """ #remove ORDER BY here
    val = []
    cols = ["Title", "Author", "Genre","Publication Year","Stock Quantity","Book ID"]
    

    if searchterm:
        sql += """ AND bk_title ILIKE %s"""
        val += [f"%{searchterm}%"]
    
    sql += """ ORDER BY bk_title """ #add ORDER BY here
    books_allbooks_atoz = db.querydatafromdatabase(sql,val,cols)

    #...