https://www.freecodecamp.org/learn/relational-database/learn-sql-by-building-a-student-database-part-1/build-a-student-database-part-1

-insert_data.sh

#!/bin/bash

# Script to insert data from courses.csv and students.csv into students database

PSQL="psql -X --username=freecodecamp --dbname=students --no-align --tuples-only -c"
echo $($PSQL "TRUNCATE students, majors, courses, majors_courses")

cat courses.csv | while IFS="," read MAJOR COURSE
do
  if [[ $MAJOR != "major" ]]
  then
    # get major_id
    MAJOR_ID=$($PSQL "SELECT major_id FROM majors WHERE major='$MAJOR'")

    # if not found
    if [[ -z $MAJOR_ID ]]
    then
      # insert major
      INSERT_MAJOR_RESULT=$($PSQL "INSERT INTO majors(major) VALUES('$MAJOR')")
      if [[ $INSERT_MAJOR_RESULT == "INSERT 0 1" ]]
      then
        echo Inserted into majors, $MAJOR
      fi

      # get new major_id
      MAJOR_ID=$($PSQL "SELECT major_id FROM majors WHERE major='$MAJOR'")
    fi

    # get course_id
    COURSE_ID=$($PSQL "SELECT course_id FROM courses WHERE course='$COURSE'")

    # if not found
    if [[ -z $COURSE_ID ]]
    then
      # insert course
      INSERT_COURSE_RESULT=$($PSQL "INSERT INTO courses(course) VALUES('$COURSE')")
      if [[ $INSERT_COURSE_RESULT == "INSERT 0 1" ]]
      then
        echo Inserted into courses, $COURSE
      fi

      # get new course_id
      COURSE_ID=$($PSQL "SELECT course_id FROM courses WHERE course='$COURSE'")
    fi

    # insert into majors_courses
    INSERT_MAJORS_COURSES_RESULT=$($PSQL "INSERT INTO majors_courses(major_id, course_id) VALUES($MAJOR_ID, $COURSE_ID)")
    if [[ $INSERT_MAJORS_COURSES_RESULT == "INSERT 0 1" ]]
    then
      echo Inserted into majors_courses, $MAJOR : $COURSE
    fi
  fi
done

cat students.csv | while IFS="," read FIRST LAST MAJOR GPA
do
  if [[ $FIRST != "first_name" ]]
  then
    # get major_id
    MAJOR_ID=$($PSQL "SELECT major_id FROM majors WHERE major='$MAJOR'")
    # if not found
    if [[ -z $MAJOR_ID ]]
    then
      # set to null
      MAJOR_ID=null
    fi
    
    # insert student
    INSERT_STUDENT_RESULT=$($PSQL "INSERT INTO students(first_name, last_name, major_id, gpa) VALUES('$FIRST', '$LAST', $MAJOR_ID, $GPA)")
    if [[ $INSERT_STUDENT_RESULT == "INSERT 0 1" ]]
    then
      echo Inserted into students, $FIRST $LAST
    fi
  fi
done

courses.csv

students.csv