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
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