现有某乎问答题目信息表issue_tb如下（其中issue_id代表问题编号，issue_type表示问题类型）：
| issue_id | issue_type |
| E001 | Education |
| E002 | Education |
| E003 | Education |
| C001 | Career |
| C002 | Career |
| C003 | Career |
| C004 | Career |
| P001 | Psychology |
| P002 | Psychology |
创作者回答情况表answer_tb如下（其中answer_date表示创作日期、author_id指创作者编号、issue_id指回答问题编号、char_len表示回答字数）：
| answer_date | author_id | issue_id | char_len |
| 2021-11-01 | 101 | E001 | 150 |
| 2021-11-01 | 101 | E002 | 200 |
| 2021-11-01 | 102 | C003 | 50 |
| 2021-11-01 | 103 | P001 | 35 |
| 2021-11-01 | 104 | C003 | 120 |
| 2021-11-01 | 105 | P001 | 125 |
| 2021-11-01 | 102 | P002 | 105 |
| 2021-11-02 | 101 | P001 | 201 |
| 2021-11-02 | 110 | C002 | 200 |
| 2021-11-02 | 110 | C001 | 225 |
| 2021-11-02 | 110 | C002 | 220 |
| 2021-11-03 | 101 | C002 | 180 |
| 2021-11-04 | 109 | E003 | 130 |
| 2021-11-04 | 109 | E001 | 123 |
| 2021-11-05 | 108 | C001 | 160 |
| 2021-11-05 | 108 | C002 | 120 |
| 2021-11-05 | 110 | P001 | 180 |
| 2021-11-05 | 106 | P002 | 45 |
| 2021-11-05 | 107 | E003 | 56 |
请你统计回答过教育类问题的用户里有多少用户回答过职场类问题，以上例子的输出结果如下：
| num |
| 1 |
示例1
输入
drop table if exists issue_tb;
CREATE TABLE issue_tb(
issue_id char(10) NOT NULL,
issue_type char(10) NOT NULL);
INSERT INTO issue_tb VALUES('E001' ,'Education');
INSERT INTO issue_tb VALUES('E002' ,'Education');
INSERT INTO issue_tb VALUES('E003' ,'Education');
INSERT INTO issue_tb VALUES('C001', 'Career');
INSERT INTO issue_tb VALUES('C002', 'Career');
INSERT INTO issue_tb VALUES('C003', 'Career');
INSERT INTO issue_tb VALUES('C004', 'Career');
INSERT INTO issue_tb VALUES('P001' ,'Psychology');
INSERT INTO issue_tb VALUES('P002' ,'Psychology');
drop table if exists answer_tb;
CREATE TABLE answer_tb(
answer_date date NOT NULL,
author_id int(10) NOT NULL,
issue_id char(10) NOT NULL,
char_len int(10) NOT NULL);
INSERT INTO answer_tb VALUES('2021-11-1', 101, 'E001' ,150);
INSERT INTO answer_tb VALUES('2021-11-1', 101, 'E002', 200);
INSERT INTO answer_tb VALUES('2021-11-1',102, 'C003' ,50);
INSERT INTO answer_tb VALUES('2021-11-1' ,103, 'P001', 35);
INSERT INTO answer_tb VALUES('2021-11-1', 104, 'C003', 120);
INSERT INTO answer_tb VALUES('2021-11-1' ,105, 'P001', 125);
INSERT INTO answer_tb VALUES('2021-11-1' , 102, 'P002', 105);
INSERT INTO answer_tb VALUES('2021-11-2', 101, 'P001' ,201);
INSERT INTO answer_tb VALUES('2021-11-2', 110, 'C002', 200);
INSERT INTO answer_tb VALUES('2021-11-2', 110, 'C001', 225);
INSERT INTO answer_tb VALUES('2021-11-2' , 110, 'C002', 220);
INSERT INTO answer_tb VALUES('2021-11-3', 101, 'C002', 180);
INSERT INTO answer_tb VALUES('2021-11-4' ,109, 'E003', 130);
INSERT INTO answer_tb VALUES('2021-11-4', 109, 'E001',123);
INSERT INTO answer_tb VALUES('2021-11-5', 108, 'C001',160);
INSERT INTO answer_tb VALUES('2021-11-5', 108, 'C002', 120);
INSERT INTO answer_tb VALUES('2021-11-5', 110, 'P001', 180);
INSERT INTO answer_tb VALUES('2021-11-5' , 106, 'P002' , 45);
INSERT INTO answer_tb VALUES('2021-11-5' , 107, 'E003', 56);输出
1
