column Posting List ==> "10 20;3 21 2; 43 100;105;......

##</code><code>##

WORD
IN_DOCUMENT
AT_POSITION

##</code><code>##

TABLE words
    word    CHAR(32) PRIMARY KEY
    word_id INT

TABLE docs
    doc_id   INT PRIMARY KEY
    doc_name VARCHAR

TABLE word_doc
    word_id  INT
    doc_id   INT
    pos      INT

##</code><code>##

CREATE INDEX warpspeed ON word_doc (word_id)

##</code><code>##

SELECT doc_id FROM word_doc WHERE word_id = ?
INTERSECT
SELECT doc_id FROM word_doc WHERE word_id = ?