##测试表结构
CREATE TABLE t (
id int NOT NULL,
a int DEFAULT NULL,
c int DEFAULT NULL,
PRIMARY KEY (id),
KEY a (a)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
CREATE TABLE t1 (
id int NOT NULL,
a int DEFAULT NULL,
b int DEFAULT NULL,
c int DEFAULT NULL,
PRIMARY KEY (id),
KEY a (a)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
###测试数据
insert into t(id,a,c) values(1,1,1);\
insert into t1(id,a,b,c) values(2,1,2,2)