### Database Schema
CREATE TABLE langs(lid    INTEGER PRIMARY KEY AUTOINCREMENT,
                            lang   TEXT UNIQUE,
                            locale TEXT UNIQUE,
                            pages  INTEGER DEFAULT 0,  -- total pages in this language
                            words  INTEGER DEFAULT 0)

CREATE TABLE sqlite_sequence(name,seq)

CREATE TABLE pages(pid INTEGER PRIMARY KEY AUTOINCREMENT,
                            lid INTEGER REFERENCES langs(lid) ON UPDATE CASCADE ON DELETE CASCADE,
                            page INTEGER DEFAULT NULL, -- wikipedia page id
                            revision INTEGER DEFAULT NULL, -- wikipedia revision page id
                            title TEXT,
                            words INTEGER DEFAULT 0, -- number of different words in this page
                            UNIQUE(lid,page,title))

CREATE TABLE words(wid INTEGER PRIMARY KEY AUTOINCREMENT,
                            word        TEXT UNIQUE,
                            occurrences INTEGER DEFAULT 0)

CREATE TABLE langs_words(lid INTEGER REFERENCES langs(lid) ON UPDATE CASCADE ON DELETE CASCADE,
                                        wid INTEGER REFERENCES words(wid) ON UPDATE CASCADE ON DELETE CASCADE,
                                        occurrences INTEGER, -- repetitions of this word in this language
                                        PRIMARY KEY(lid,wid))
                                        WITHOUT ROWID

CREATE TABLE pages_words(pid INTEGER REFERENCES pages(pid) ON UPDATE CASCADE ON DELETE CASCADE,
                                        wid INTEGER REFERENCES words(wid) ON UPDATE CASCADE ON DELETE CASCADE,
                                        occurrences INTEGER DEFAULT 0, -- times this word appears into this page
                                        PRIMARY KEY(pid,wid))
                                        WITHOUT ROWID

CREATE TABLE biwords(lid    INTEGER REFERENCES langs(lid) ON UPDATE CASCADE ON DELETE CASCADE,
                                w1st   INTEGER REFERENCES words(wid) ON UPDATE CASCADE ON DELETE CASCADE,
                                w2nd   INTEGER REFERENCES words(wid) ON UPDATE CASCADE ON DELETE CASCADE,
                                occurrences INTEGER DEFAULT 0, -- times this pair appears in this language/page
                                PRIMARY KEY(lid,w1st,w2nd))
                                WITHOUT ROWID

### Question
How much higher in percentage does the word "grec" occur on the page titled "Àbac" than on the page titled "Astronomia"?

### Hint
grec refers to word = 'grec'; Àbac refers to title = 'Àbac'; Astronomia refers to title = 'Astronomia'; percentage = DIVIDE(SUBTRACT(occurrences where title = 'Àbac' AND word = 'grec', occurrences where title = 'Astronomia' AND word = 'grec'), occurrences where title = 'Astronomia' AND word = 'grec')

### SQL
SELECT CAST((SUM(CASE WHEN T3.title = 'Àbac' THEN T2.occurrences END) - SUM(CASE WHEN T3.title = 'Astronomia' THEN T2.occurrences END)) AS REAL) * 100 / SUM(CASE WHEN T3.title = 'Astronomia' THEN T2.occurrences END) FROM words AS T1 INNER JOIN pages_words AS T2 ON T1.wid = T2.wid INNER JOIN pages AS T3 ON T2.pid = T3.pid WHERE T1.word = 'grec'