left join时筛选条件对查询结果的

-- 创建表
CREATE TABLE `table1`
(
    `id`          int(11) NOT NULL AUTO_INCREMENT,
    `card_num`    varchar(60) DEFAULT NULL,
    `customer_id` varchar(60) DEFAULT NULL,
    PRIMARY KEY (`id`)
) ENGINE = InnoDB
  AUTO_INCREMENT = 12
  DEFAULT CHARSET = utf8mb4 COMMENT ='测试表1';

-- 创建表
CREATE TABLE `table2`
(
    `id`          int(11)     NOT NULL AUTO_INCREMENT,
    `customer_id` varchar(60) DEFAULT NULL,
    `type`        varchar(60) DEFAULT NULL COMMENT '联系方式',
    `phone`       varchar(60) NOT NULL COMMENT '联系号码',
    PRIMARY KEY (`id`)
) ENGINE = InnoDB
  AUTO_INCREMENT = 12
  DEFAULT CHARSET = utf8mb4 COMMENT ='测试表2';

-- 插入数据
insert into table1
values (1, 6223123456781001, 1001)
insert into table1
values (2, 6223123456781002, 1002)
insert into table1
values (3, 6223123456781003, 1003)

-- 插入数据
insert into table2
values (1, 1001, 1, 010 - 78586)
insert into table2
values (2, 1001, 2, 18810123456)
insert into table2
values (3, 1002, 1, 010 - 837433)
insert into table2
values (4, 1003, 1, 010 - 837433)

-- 筛选条件在最外层
select t1.card_num, t2.phone, t2.type
from table1 t1
         left join ssm.table2 t2 on t1.customer_id = t2.customer_id
where t2.type = '2'

-- 筛序条件在内层
select t1.card_num, t2.phone,t2.type
from table1 t1
         left join (select * from table2
where type = '2') t2 on t1.customer_id = t2.customer_id

创建的表格：

table1

table2

结果：