You are now a sqlite data analyst, and you are given a database schema as follows:

    【Schema】
    【DB_ID】 professional_basketball
【Schema】
# Table: awards_players
[
(playerID:TEXT, Primary Key, Examples: [abdulka01, abdulma02, adamsal01]),
(award:TEXT, Primary Key, Examples: [All-Defensive Second Team]),
(year:INTEGER, Primary Key, Examples: [1969, 1970, 1971]),
(lgID:TEXT, Examples: [NBA, ABA, NBL]),
(note:TEXT, Examples: [tie]),
(pos:TEXT, Examples: [C, F, G])
]
# Table: player_allstar
[
(playerID:TEXT, Primary Key, Examples: [abdulka01, abdursh01, adamsal01]),
(last_name:TEXT, Examples: [Abdul-Jabbar, A-Rahim, Adams]),
(first_name:TEXT, Examples: [Kareem, Shareef, Alvan]),
(season_id:INTEGER, Primary Key, Examples: [1969, 1970, 1971]),
(conference:TEXT, Examples: [East, West, Weset]),
(league_id:TEXT, Examples: [NBA, ABA]),
(games_played:INTEGER, Examples: [1]),
(minutes:INTEGER, Examples: [18, 30, 19]),
(points:INTEGER, Examples: [10, 19, 12]),
(o_rebounds:INTEGER, Examples: [1, 2, 0]),
(d_rebounds:INTEGER, Examples: [2, 5, 0]),
(rebounds:INTEGER, Examples: [11, 14, 7]),
(assists:INTEGER, Examples: [4, 1, 2]),
(steals:INTEGER, Examples: [3, 0, 1]),
(blocks:INTEGER, Examples: [2, 0, 1]),
(turnovers:INTEGER, Examples: [1, 0, 3]),
(personal_fouls:INTEGER, Examples: [3, 2, 0]),
(fg_attempted:INTEGER, Examples: [8, 16, 10]),
(fg_made:INTEGER, Examples: [4, 8, 5]),
(ft_attempted:INTEGER, Examples: [2, 4, 0]),
(ft_made:INTEGER, Examples: [2, 3, 0]),
(three_attempted:INTEGER, Examples: [0, 1, 6]),
(three_made:INTEGER, Examples: [0, 1, 3])
]
# Table: draft
[
(id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(draftYear:INTEGER, Examples: [1967, 1968, 1969]),
(draftRound:INTEGER, Examples: [0, 1, 2]),
(draftSelection:INTEGER, Examples: [0, 3, 4]),
(draftOverall:INTEGER, Examples: [0, 3, 4]),
(tmID:TEXT, Examples: [ANA, DNR, DLC]),
(firstName:TEXT, Examples: [Darrell, Bob, Mike]),
(lastName:TEXT, Examples: [Hardy, Krulish, Lewis]),
(suffixName:TEXT, Examples: [Jr.]),
(playerID:TEXT, Examples: [hardyda01, lewisbo01, lynnmi01]),
(draftFrom:TEXT, Examples: [Baylor, Pacific, North Carolina]),
(lgID:TEXT, Examples: [ABA, NBA])
]
# Table: players_teams
[
(id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(playerID:TEXT, Examples: [abdelal01, abdulka01, abdulma01]),
(year:INTEGER, Examples: [1990, 1991, 1992]),
(stint:INTEGER, Examples: [1, 2, 0]),
(tmID:TEXT, Examples: [POR, MIL, BOS]),
(lgID:TEXT, Examples: [NBA, NBL, ABA]),
(GP:INTEGER, Examples: [43, 71, 12]),
(GS:INTEGER, Examples: [0, 69, 62]),
(minutes:INTEGER, Examples: [290, 934, 159]),
(points:INTEGER, Examples: [135, 432, 64]),
(oRebounds:INTEGER, Examples: [27, 81, 12]),
(dRebounds:INTEGER, Examples: [62, 179, 25]),
(rebounds:INTEGER, Examples: [89, 260, 37]),
(assists:INTEGER, Examples: [12, 30, 10]),
(steals:INTEGER, Examples: [4, 25, 6]),
(blocks:INTEGER, Examples: [12, 17, 4]),
(turnovers:INTEGER, Examples: [22, 66, 0]),
(PF:INTEGER, Examples: [39, 132, 24]),
(fgAttempted:INTEGER, Examples: [116, 361, 56]),
(fgMade:INTEGER, Examples: [55, 178, 26]),
(ftAttempted:INTEGER, Examples: [44, 101, 16]),
(ftMade:INTEGER, Examples: [25, 76, 12]),
(threeAttempted:INTEGER, Examples: [0, 1, 2]),
(threeMade:INTEGER, Examples: [0, 1, 24]),
(PostGP:INTEGER, Examples: [5, 8, 0]),
(PostGS:INTEGER, Examples: [0, 6, 3]),
(PostMinutes:INTEGER, Examples: [13, 25, 0]),
(PostPoints:INTEGER, Examples: [4, 12, 0]),
(PostoRebounds:INTEGER, Examples: [1, 0, 2]),
(PostdRebounds:INTEGER, Examples: [2, 4, 0]),
(PostRebounds:INTEGER, Examples: [3, 4, 0]),
(PostAssists:INTEGER, Examples: [0, 2, 1]),
(PostSteals:INTEGER, Examples: [0, 20, 19]),
(PostBlocks:INTEGER, Examples: [0, 1, 39]),
(PostTurnovers:INTEGER, Examples: [0, 2, 9]),
(PostPF:INTEGER, Examples: [0, 4, 7]),
(PostfgAttempted:INTEGER, Examples: [6, 10, 0]),
(PostfgMade:INTEGER, Examples: [2, 5, 0]),
(PostftAttempted:INTEGER, Examples: [0, 4, 101]),
(PostftMade:INTEGER, Examples: [0, 2, 74]),
(PostthreeAttempted:INTEGER, Examples: [0, 1, 2]),
(PostthreeMade:INTEGER, Examples: [0, 12, 2]),
(note:TEXT, Examples: [C])
]
# Table: players
[
(playerID:TEXT, Primary Key, Examples: [abdelal01, abdulka01, abdulma01]),
(useFirst:TEXT, Examples: [Alaa, Kareem, Mahdi]),
(firstName:TEXT, Examples: [Alaa, Kareem, Mahdi]),
(middleName:TEXT, Examples: [Shareef, Craig, Edward]),
(lastName:TEXT, Examples: [Abdelnaby, Abdul-Jabbar, Abdul-Rahman]),
(nameGiven:TEXT, Examples: [nameGiven, Mort, Robert]),
(fullGivenName:TEXT, Examples: [Ferdinand Lewis Alcindor, Jr.]),
(nameSuffix:TEXT, Examples: [Jr., III, nameSuffix]),
(nameNick:TEXT, Examples: [Lew, Cap, Walt, Don, The Kangaroo]),
(pos:TEXT, Examples: [F-C, C, G]),
(firstseason:INTEGER, Examples: [0, 1951]),
(lastseason:INTEGER, Examples: [0, 1951]),
(height:REAL, Examples: [82.0, 85.0, 74.0]),
(weight:INTEGER, Examples: [240, 225, 185]),
(college:TEXT, Examples: [Duke, UCLA, Louisiana State]),
(collegeOther:TEXT, Examples: [Santa Monica City, Michigan, Louisville]),
(birthDate:DATE, Examples: [1968-06-24]),
(birthCity:TEXT, Examples: [Cairo, New York, Wilmington]),
(birthState:TEXT, Examples: [NY, DE, MS]),
(birthCountry:TEXT, Examples: [EGY, USA, FRA]),
(highSchool:TEXT, Examples: [Bloomfield Senior, Power Memorial, Overbrook / Moton]),
(hsCity:TEXT, Examples: [Bloomfield]),
(hsState:TEXT, Examples: [NJ, NY, PA / MD]),
(hsCountry:TEXT, Examples: [USA, FRA, NGR]),
(deathDate:DATE),
(race:TEXT, Examples: [B, W, O])
]
# Table: coaches
[
(coachID:TEXT, Primary Key, Examples: [adelmri01, adubari01, aingeda01]),
(year:INTEGER, Primary Key, Examples: [1988, 1989, 1990]),
(tmID:TEXT, Primary Key, Examples: [POR, GSW, SAC]),
(lgID:TEXT, Examples: [NBA, ABA, ABL1]),
(stint:INTEGER, Primary Key, Examples: [2, 1, 4]),
(won:INTEGER, Examples: [14, 59, 63]),
(lost:INTEGER, Examples: [21, 23, 19]),
(post_wins:INTEGER, Examples: [0, 12, 9]),
(post_losses:INTEGER, Examples: [3, 9, 7])
]
# Table: awards_coaches
[
(id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(year:INTEGER, Examples: [1962, 1963, 1964]),
(coachID:TEXT, Examples: [gallaha01, hannual01, auerbre01]),
(award:TEXT, Examples: [NBA Coach of the Year]),
(lgID:TEXT, Examples: [NBA, ABA]),
(note:TEXT, Examples: [tie])
]
# Table: series_post
[
(id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(year:INTEGER, Examples: [1946, 1947, 1948]),
(round:TEXT, Examples: [F, QF, SF]),
(series:TEXT, Examples: [O, M, N]),
(tmIDWinner:TEXT, Examples: [PHW, NYK, CHS]),
(lgIDWinner:TEXT, Examples: [NBA, ABA]),
(tmIDLoser:TEXT, Examples: [CHS, CLR, STB]),
(lgIDLoser:TEXT, Examples: [NBA, ABA]),
(W:INTEGER, Examples: [4, 2, 1]),
(L:INTEGER, Examples: [1, 0, 2])
]
# Table: teams
[
(year:INTEGER, Primary Key, Examples: [1937, 1938, 1939]),
(lgID:TEXT, Examples: [NBL, NBA, PBLA]),
(tmID:TEXT, Primary Key, Examples: [AFS, AGW, BFB]),
(franchID:TEXT, Examples: [AFS, AGW, BFB]),
(confID:TEXT, Examples: [EC, WC]),
(divID:TEXT, Examples: [EA, WE, ED]),
(rank:INTEGER, Examples: [1, 2, 4]),
(confRank:INTEGER, Examples: [0, 4, 3]),
(playoff:TEXT, Examples: [CF, WC, LC]),
(name:TEXT, Examples: [Akron Firestone Non-Skids]),
(o_fgm:INTEGER, Examples: [249, 243, 108]),
(o_ftm:INTEGER, Examples: [183, 159, 46]),
(o_pts:INTEGER, Examples: [681, 645, 262]),
(d_pts:INTEGER, Examples: [578, 498, 275]),
(homeWon:INTEGER, Examples: [8, 2, 3]),
(homeLost:INTEGER, Examples: [1, 2, 3]),
(awayWon:INTEGER, Examples: [5, 1, 0]),
(awayLost:INTEGER, Examples: [3, 4, 5]),
(won:INTEGER, Examples: [14, 13, 3]),
(lost:INTEGER, Examples: [4, 5, 6]),
(games:INTEGER, Examples: [18, 9, 10]),
(arena:TEXT, Examples: [Boston Garden, Chicago Stadium, Cleveland Arena])
]
【Foreign keys】
awards_players.playerID=players.playerID
player_allstar.playerID=players.playerID
draft.tmID=teams.tmID
draft.draftYear=teams.year
players_teams.tmID=teams.tmID
players_teams.year=teams.year
players_teams.playerID=players.playerID
coaches.tmID=teams.tmID
coaches.year=teams.year
awards_coaches.coachID=coaches.coachID
awards_coaches.year=coaches.year
series_post.tmIDWinner=teams.tmID
series_post.year=teams.year
series_post.tmIDLoser=teams.tmID
series_post.year=teams.year

    【Question】
    How many players, in games played in 1990, achieved 50% or less of oRebounds than dRebounds. in 1990 refers to season_id = 1990; 50% or less of oRebounds than dRebounds refers to o_rebounds < = multiply(d_rebounds, 0.5)

    【Evidence】
    in 1990 refers to season_id = 1990; 50% or less of oRebounds than dRebounds refers to o_rebounds < = multiply(d_rebounds, 0.5)

    Please read and understand the database schema carefully, and generate an executable SQL based on the user's question and evidence. 

SQL: SELECT COUNT(playerID) FROM players_teams WHERE CAST(oRebounds AS REAL) * 100 / dRebounds <= 50 AND year = 1990