Task: NL2SQL (source dataset: Spider)

Natural language to SQL, also known as NL2SQL, is the problem of generating a SQL query that can be executed on a input table, for a given natural language question.

You will be given an input table called "table" in the markdown format, as well as a question. Your task is to generate an SQL query that can be executed on the input table to answer the question.

Please ensure that the generated SQL only return relevant columns being specifically asked in the question (e.g., in SQL please don't return more than one columns in SELECT if only one column is needed to answer the given question, and similarly please refrain from using SELECT * unless the entire row is needed to answer the question).
 
When generating SQL code, please use the SQLite syntax to ensure that your SQL is executable on SQLite3. Use only columns that are present in the table, always use quotes around your column and table names (some column names have punctuation or special characters), and refer to the columns using the column-names exactly as they appear in the table, do not add or remove punctuation (underscore, slash, etc.)

No explanation, return the code only with the following markdown codeblock format : ```sql<SQL CODE>```. For example, ```sql
SELECT * FROM "table"
``` is a valid format.

Database:
online_exams

Tables:

Table: Students
|   Student_ID | First_Name   | Middle_Name   | Last_Name   | Gender_MFU   | Student_Address                  | Email_Adress                 | Cell_Mobile_Phone   | Home_Phone           |
|-------------:|:-------------|:--------------|:------------|:-------------|:---------------------------------|:-----------------------------|:--------------------|:---------------------|
|            5 | Wilbert      | Mia           | Conroy      | F            | 2908 Breana Streets Suite 638    | rjast@example.com            | 620.962.4384x340    | 017-084-5752x96504   |
|            6 | Abdul        | Era           | Renner      | M            | 009 Vandervort Ferry             | green.jesus@example.net      | 03437137203         | (054)515-8842x4046   |
|           11 | Ari          | Jacinthe      | Kessler     | M            | 053 Candido Port Suite 568       | oschamberger@example.net     | 207-458-7971        | 220.735.2352x52387   |
|           15 | Cassidy      | Karson        | Gerhold     | U            | 25250 Alexander Spring Apt. 106  | alvera52@example.com         | 1-077-467-7564      | 715.670.8396x276     |
|           17 | Alfreda      | Queen         | Schuster    | M            | 1110 Kaylee Greens Apt. 491      | bogan.barton@example.net     | 038-482-3730x66922  | 1-400-038-3818x39652 |
|           22 | Betsy        | Larue         | Orn         | M            | 71938 Dickinson Summit Suite 683 | jana90@example.com           | 1-922-743-4349      | 377-581-9036         |
|           24 | Yadira       | Matteo        | Rohan       | U            | 3679 Huels Ranch                 | gusikowski.retta@example.net | 084-076-8037x1728   | 743.322.8573x380     |
|           35 | Deven        | Gino          | Deckow      | U            | 49860 Cesar Pine                 | ezekiel53@example.com        | +08(7)2834974200    | +23(7)3611361591     |
|           37 | Haylie       | Rupert        | Wiegand     | U            | 988 Hettinger Pine Apt. 005      | kschroeder@example.org       | 1-185-860-6666x236  | 048.938.2113x0806    |
|           38 | Jeromy       | Rebekah       | Torp        | F            | 59773 Misty Loop                 | dhermiston@example.net       | 1-197-438-2369      | 015.452.3914         |


Table: Questions
|   Question_ID | Type_of_Question_Code   | Question_Text                                    |
|--------------:|:------------------------|:-------------------------------------------------|
|           285 | Single Choice           | When is middle age period                        |
|           321 | Multiple Choice         | Who are from Renaissance age                     |
|           585 | Multiple Choice         | Which are the works from Picasso                 |
|           603 | Multiple Choice         | Which are the works from Van Gogh                |
|           613 | Multiple Choice         | Which are answers for the blanks in the passage  |
|           655 | Multiple Choice         | Which are answers for the blanks in the passage  |
|           682 | Multiple Choice         | Which are answers for the blanks in the passage? |
|           710 | Free Text               | Is it true that queue is FIFO                    |
|           721 | Multiple Choice         | Choose which structures are linear               |
|           839 | Single Choice           | Choose the definition of a foreign key           |


Table: Exams
|   Exam_ID | Subject_Code   | Exam_Date           | Exam_Name       |
|----------:|:---------------|:--------------------|:----------------|
|         1 | Art History    | 2016-01-28 02:03:40 | 2016 Spring AH  |
|         2 | Art History    | 2017-11-17 09:21:31 | 2017 Fall AH    |
|         3 | English        | 2016-12-19 02:40:33 | 2016 Winter ENG |
|         4 | Database       | 2016-06-17 07:20:06 | 2016 Summer DB  |
|         5 | Database       | 2017-02-26 11:19:52 | 2017 Spring DB  |
|         6 | Art History    | 2016-08-10 21:39:15 | 2016 Summer AH  |
|         7 | Database       | 2017-08-25 07:48:19 | 2017 Summer DB  |
|         8 | Database       | 2015-08-21 22:15:06 | 2015 Summer DB  |
|         9 | Data Structure | 2017-08-04 05:43:39 | 2017 Summer DS  |


Table: Questions_in_Exams
|   Exam_ID |   Question_ID |
|----------:|--------------:|
|         1 |           321 |
|         1 |           285 |
|         2 |           585 |
|         2 |           603 |
|         3 |           613 |
|         3 |           682 |
|         3 |           655 |
|         9 |           710 |
|         9 |           721 |
|         8 |           839 |


Table: Valid_Answers
|   Valid_Answer_ID |   Question_ID | Valid_Answer_Text   |
|------------------:|--------------:|:--------------------|
|                 1 |           321 | ABC                 |
|                 2 |           721 | ABC                 |
|                 3 |           996 | C                   |
|                 4 |           839 | C                   |
|                 5 |           285 | C                   |
|                 6 |           613 | ABC                 |
|                 7 |           603 | ABC                 |
|                 8 |           721 | ABC                 |
|                 9 |           285 | C                   |
|                10 |           655 | ABC                 |


Table: Student_Answers
|   Student_Answer_ID |   Exam_ID |   Question_ID |   Student_ID | Date_of_Answer      | Comments   |   Satisfactory_YN | Student_Answer_Text   |
|--------------------:|----------:|--------------:|-------------:|:--------------------|:-----------|------------------:|:----------------------|
|                 127 |         1 |           321 |           52 | 2017-08-13 06:03:03 | Normal     |                 0 | D                     |
|                 149 |         1 |           285 |           22 | 2017-07-27 06:34:17 | Normal     |                 1 | ABC                   |
|                 169 |         2 |           585 |           40 | 2017-07-30 12:07:59 | Normal     |                 1 | ABC                   |
|                 284 |         2 |           603 |           35 | 2018-02-21 09:14:48 | Normal     |                 1 | ABC                   |
|                 374 |         3 |           655 |            6 | 2017-12-04 10:10:48 | Normal     |                 1 | ABC                   |
|                 397 |         3 |           613 |           52 | 2017-12-21 16:40:17 | Normal     |                 0 | BCD                   |
|                 455 |         3 |           682 |           15 | 2017-05-13 07:29:20 | Normal     |                 1 | ABC                   |
|                 460 |         9 |           721 |           93 | 2018-01-10 21:22:57 | Normal     |                 0 | AC                    |
|                 544 |         8 |           839 |            6 | 2017-11-04 00:23:29 | Normal     |                 1 | C                     |
|                 564 |         8 |           856 |           22 | 2017-07-27 18:22:08 | Normal     |                 1 | C                     |


Table: Student_Assessments
|   Student_Answer_ID |   Valid_Answer_ID | Student_Answer_Text   |   Satisfactory_YN | Assessment   |
|--------------------:|------------------:|:----------------------|------------------:|:-------------|
|                 162 |                 3 | B                     |                 0 | Very Good    |
|                 172 |                 4 | B                     |                 0 | Excellent    |
|                   2 |                 3 | A                     |                 1 | Very Good    |
|                 307 |                 2 | True                  |                 0 | Very Good    |
|                 340 |                 3 | False                 |                 1 | OK           |
|                 421 |                 1 | B                     |                 1 | Excellent    |
|                 438 |                 2 | True                  |                 0 | Excellent    |
|                 518 |                 3 | B                     |                 0 | OK           |
|                 536 |                 4 | A                     |                 1 | Excellent    |
|                 540 |                 5 | True                  |                 1 | OK           |


Question: How many different comments are there for student answers?

db_id: online_exams
tables: name: Students
data: Students.csv
name: Questions
data: Questions.csv
name: Exams
data: Exams.csv
name: Questions_in_Exams
data: Questions_in_Exams.csv
name: Valid_Answers
data: Valid_Answers.csv
name: Student_Answers
data: Student_Answers.csv
name: Student_Assessments
data: Student_Assessments.csv
label: SELECT count(DISTINCT Comments) FROM Student_Answers
sqlite_path: $MMTU_HOME/data_sqlite/spider/spider_data/test_database/online_exams/online_exams.sqlite