Add DROP TABLE IF EXISTS.

main/install/db_main.sql

@@ -3464,8 +3464,10 @@ CREATE TABLE track_e_attempt_coeff (
 );
 
 -- Course
-
+DROP TABLE IF EXISTS c_student_publication_rel_document;
 CREATE TABLE IF NOT EXISTS c_student_publication_rel_document (id  INT PRIMARY KEY NOT NULL AUTO_INCREMENT, work_id INT NOT NULL, document_id INT NOT NULL, c_id INT NOT NULL);
+DROP TABLE IF EXISTS c_student_publication_rel_user;
 CREATE TABLE IF NOT EXISTS c_student_publication_rel_user ( id  INT PRIMARY KEY NOT NULL AUTO_INCREMENT, work_id INT NOT NULL, user_id INT NOT NULL, c_id INT NOT NULL);
+DROP TABLE IF EXISTS c_student_publication_comment;
 CREATE TABLE IF NOT EXISTS c_student_publication_comment ( id INT PRIMARY KEY NOT NULL AUTO_INCREMENT, work_id INT NOT NULL, c_id INT NOT NULL, comment text, file VARCHAR(255), user_id int NOT NULL, sent_at datetime NOT NULL);