SAS 中的 sql 语句的使用------多表使用

SAS 中的多表使用一般为多表之间的连接查询

连接查询分为：

（1）表内连接

（2）表与表之间的连接

这里我们只讨论表与表之间的连接，而表与表之间的连接分为：

（1）全连接

　　这里的全连接就是基本的笛卡尔积，笛卡尔积通俗一点说就是每条数据的交叉相乘，使用full join

data temp;
input visit $ visit_dat $ age type $;
cards;
v1 20190201 18 a
v2 20200304 21 f
v3 20190825 34 e
v1 20180431 58 c
v2 20170902 23 d
v4 20160826 25 r
;
run;

data temp2;
input visit $ visit_dat $ age type $;
cards;
v3 20190725 25 d
v4 20200431 35 e
v5 20190921 38 g
;
run;

/* 创建表,含条件语句 */
proc sql;
create table join_visit as
select
    table1.visit as visit1,
    table1.visit_dat as visit_dat1,
    table1.age as age1,
    table1.type as type1,
    table2.visit as visit1,
    table2.visit_dat as visit_dat2,
    table2.age as age2,
    table2.type as type2
from
    work.temp as table1
full join
    work.temp2 as table2
on 
    table1.visit = table2.visit;
run;

/* 打印创建的表 */
proc print data=join_visit;
run;

结果为：

（2）左外连接

　　保留左边的所有数据，对于右边的，只保留符合条件的数据，使用 left join

data temp;
input visit $ visit_dat $ age type $;
cards;
v1 20190201 18 a
v2 20200304 21 f
v3 20190825 34 e
v1 20180431 58 c
v2 20170902 23 d
v4 20160826 25 r
;
run;

data temp2;
input visit $ visit_dat $ age type $;
cards;
v3 20190725 25 d
v4 20200431 35 e
v5 20190921 38 g
;
run;

/* 创建表,含条件语句 */
proc sql;
create table join_visit as
select
    table1.visit as visit1,
    table1.visit_dat as visit_dat1,
    table1.age as age1,
    table1.type as type1,
    table2.visit as visit1,
    table2.visit_dat as visit_dat2,
    table2.age as age2,
    table2.type as type2
from
    work.temp as table1
left join
    work.temp2 as table2
on 
    table1.visit = table2.visit;
run;

/* 打印创建的表 */
proc print data=join_visit;
run;

（3）右外连接

　　保留右边的所有数据，对于左边的，只保留符合条件的数据，使用 right join

data temp;
input visit $ visit_dat $ age type $;
cards;
v1 20190201 18 a
v2 20200304 21 f
v3 20190825 34 e
v1 20180431 58 c
v2 20170902 23 d
v4 20160826 25 r
;
run;

data temp2;
input visit $ visit_dat $ age type $;
cards;
v3 20190725 25 d
v4 20200431 35 e
v5 20190921 38 g
;
run;

/* 创建表,含条件语句 */
proc sql;
create table join_visit as
select
    table1.visit as visit1,
    table1.visit_dat as visit_dat1,
    table1.age as age1,
    table1.type as type1,
    table2.visit as visit1,
    table2.visit_dat as visit_dat2,
    table2.age as age2,
    table2.type as type2
from
    work.temp as table1
right join
    work.temp2 as table2
on 
    table1.visit = table2.visit;
run;

/* 打印创建的表 */
proc print data=join_visit;
run;

结果为：

 注意：

要注意的是，多表连接使用的时候，重要的不是语句的使用，而是选择哪一个连接，才是最重要的。