Number courses taught Fall semester but never Spring

Write a SQL statement to find out the number of courses which have been taught in Fall semester but never in Spring semester.

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Database schema

CREATE TABLE "public"."prereq" (
    "course_id" varchar(8) NOT NULL,
    "prereq_id" varchar(8) NOT NULL,
    PRIMARY KEY ("course_id","prereq_id")
);

CREATE TABLE "public"."classroom" (
    "building" varchar(15) NOT NULL,
    "room_number" varchar(7) NOT NULL,
    "capacity" numeric(4,0),
    PRIMARY KEY ("building","room_number")
);

CREATE TABLE "public"."student" (
    "id" varchar(5) NOT NULL,
    "name" varchar(20) NOT NULL,
    "dept_name" varchar(20),
    "tot_cred" numeric(3,0) CHECK (tot_cred >= (0)::numeric),
    PRIMARY KEY ("id")
);

CREATE TABLE "public"."takes" (
    "id" varchar(5) NOT NULL,
    "course_id" varchar(8) NOT NULL,
    "sec_id" varchar(8) NOT NULL,
    "semester" varchar(6) NOT NULL,
    "year" numeric(4,0) NOT NULL,
    "grade" varchar(2),
    PRIMARY KEY ("id","course_id","sec_id","semester","year")
);

CREATE TABLE "public"."department" (
    "dept_name" varchar(20) NOT NULL,
    "building" varchar(15),
    "budget" numeric(12,2) CHECK (budget > (0)::numeric),
    PRIMARY KEY ("dept_name")
);

CREATE TABLE "public"."time_slot" (
    "time_slot_id" varchar(4) NOT NULL,
    "day" varchar(1) NOT NULL,
    "start_hr" numeric(2,0) NOT NULL CHECK ((start_hr >= (0)::numeric) AND (start_hr < (24)::numeric)),
    "start_min" numeric(2,0) NOT NULL CHECK ((start_min >= (0)::numeric) AND (start_min < (60)::numeric)),
    "end_hr" numeric(2,0) CHECK ((end_hr >= (0)::numeric) AND (end_hr < (24)::numeric)),
    "end_min" numeric(2,0) CHECK ((end_min >= (0)::numeric) AND (end_min < (60)::numeric)),
    PRIMARY KEY ("time_slot_id","day","start_hr","start_min")
);

CREATE TABLE "public"."course" (
    "course_id" varchar(8) NOT NULL,
    "title" varchar(50),
    "dept_name" varchar(20),
    "credits" numeric(2,0) CHECK (credits > (0)::numeric),
    PRIMARY KEY ("course_id")
);

CREATE TABLE "public"."section" (
    "course_id" varchar(8) NOT NULL,
    "sec_id" varchar(8) NOT NULL,
    "semester" varchar(6) NOT NULL CHECK ((semester)::text = ANY (ARRAY[('Fall'::character varying)::text, ('Winter'::character varying)::text, ('Spring'::character varying)::text, ('Summer'::character varying)::text])),
    "year" numeric(4,0) NOT NULL CHECK ((year > (1701)::numeric) AND (year < (2100)::numeric)),
    "building" varchar(15),
    "room_number" varchar(7),
    "time_slot_id" varchar(4),
    PRIMARY KEY ("course_id","sec_id","semester","year")
);

CREATE TABLE "public"."teaches" (
    "id" varchar(5) NOT NULL,
    "course_id" varchar(8) NOT NULL,
    "sec_id" varchar(8) NOT NULL,
    "semester" varchar(6) NOT NULL,
    "year" numeric(4,0) NOT NULL,
    PRIMARY KEY ("id","course_id","sec_id","semester","year")
);

CREATE TABLE "public"."instructor" (
    "id" varchar(5) NOT NULL,
    "name" varchar(20) NOT NULL,
    "dept_name" varchar(20),
    "salary" numeric(8,2) CHECK (salary > (29000)::numeric),
    PRIMARY KEY ("id")
);

CREATE TABLE "public"."advisor" (
    "s_id" varchar(5) NOT NULL,
    "i_id" varchar(5),
    PRIMARY KEY ("s_id")
);