The Bluesier Side Of Jazz for Piano/Keyboards by Andrew D. Gordon

...and that is exactly at the top of the page 4, on the first example he gives, when the tonality is D Major 'Basic Major Blues Solo Riffs', but, the beginner musician doesn't know why a major chord whose 3rd is major (F#) has in the melody an altered F (when it should be E#), but it's not because most people write wrong over time that things get right, the human being has an incredible tendency to make repeated errors to what we call 'historical constant errors', since we know that the tendency of most people to be stupid is always accurate.

Many non-musicians have been writing music books for decades, the rule is they didn't have a good education to be a musician, so they write a book, this way their families don't realize their incompetences. So wasting time reading bad books slows you to reach your goals.

The author 'A.D G' could have written the harmony correctly: when in the chord D7 on page 4, the correct one would be D7 #9, since the melody is also over this augmented 9 (#9) of this chord, looking to it seems to be D minor on the melody, then the harmony goes to the chord IV = G7

This '#9' belonging to D chord, with the melody on the written 'natural F, but E#' that leads the Blues with its greater identity, is one of the spiral components of the Blues DNA, of course no book brings this, and unfortunately you will only play but will never know the reason for it, how frustrating.
Although the minor seventh chords of the Blues don't have a dominant function, there will always be a single chord in the middle of the musical discourse that has this dominant function, as is this chord in question (D7 #9), whose 9 and 13 changed or not only happen in a dominant chord, this is the clue that the tonality is not D major but G major, since in Blue it is easy to lose the tonal axis, so this tonality could also be written G major. The G7 chord could have the major 9 (G7 9) or not, because the melody rests on that 9 of this G-chord on his example on page 4..

The axis is lost because the Blue's lament text is so repetitive and goes through 'n' melodies and the tendency for repetition can cause a fade-out in harmonic structure 'I-IV', when the ' I ' chord in D major becoming a secondary dominant: ' i = V7 / IV7 ' in which this 'IV 7' loses the dominant harmony function, to aid in the monotony of the Blues text.

Only on page 24 does the author write a single chord with the augmented 9 (D 7 # 9 b9) that has nothing to do with my quote on Blues DNA, and in the 3rd system of this same page, he simply writes a 'F9 chord', when it should be F6 9.

Anyway, it may be interesting to touch these small examples and bring some pleasure, but, forget learning some rules the book will not give you, is a book to play, not to understand the functions of harmony and why of having 9ªs and 6ªs in the chords.