【SAS ADVANCE】Performing Queries Using PROC SQL

SQL: Structured Query Language

一、Objectives in this chapter:

• invoke the SQL procedure
• select columns
• define new columns
• specify the table(s) to read
• specify subsetting criteria
• order rows by values of one or more columns
• group results by values of one or more columns
• end the SQL procedure
• summarize data 
• generate a report as the output of a query
• create a table of the output of a query

二、PROC SQL有何不同？

• 与其他PROC步骤不同的是，PROC SQL由很多个子句构成。最常见的情形是PROC SQL代码中包含两个语句：第一季是PROC SQL;第二季是SELECT语句，而SELECT语句中就包含多了子句，例如：SELECT ...,.. FROM ...,....WEHER和ORDER BY;
• PROC SQL过程不需要RUN语句，PROC SQL自动执行每一个查询；
• 建议在末尾加上QUIT语句来结束运行；

三、PROC SQL的基本格式

LIBNAME libref 'SAS-data-library';
1 PROC SQL;                                             /*invoke the SQL procedure*/      
2    CREATE TABLE table-name AS                            

    SELECT column-1<,...,column-n>                   /*specifies the column(s) to be selectd*/
       from table-1|view-1<,...,table-n|view-n>      /*specifies the table(s) to be queried*/
       <WHERE expression>                            /*subsets the data based on a condition*/
       <GROUP BY column-1<,...column-n>>             /*classifies the data into groups based  on the specifyed column*/
        <ORDER BY column-1<,...column-n>>;           /*sorts the rows that the query returns by the values of the specified columns*/
8  QUIT;

 【注意事项】：

    SELECT语句包含多个子句，以分号结束

四、PROC SQL输出

PROC SQL语句	TYPE Of Output
SELECT	report
CREATE TABLE and SELECT	table
CREATE VIEW AND SELECT	PROC SQL VIEW

 五、Order by语句中的编程注意事项

1) 常常放在select语句的最后；
2) 若用户需要逆序排序，则需将关键词DESC放在order by语句中需要逆序排列的变量后面，例如：

order by jobcode desc;

3) 在order by子句中，用户可通过指定select语句中变量的位置来代替其变量名，例如：

proc sql;
     select empid,jobcode,salary,salary*.06 as bonus
     from sasuser.payrollmaster
     where salary<32000
     order by 2;

4）在order by语句中，通过逗号列出变量，进行多变量排序

 proc sql;
      select empid,jobcode,salary,salary*.06 as bonus
      from sasuser.payrollmaster
      where salary<32000
      order by jobcode,empid;/order by 2,empid;

六、join two or more tables 

• 若需要join两个或多个tables，list the columns that you want to select from both tables in the SELECT clause.
• Seperate all column names with commas.
• 若用户需要引用的变量名出现在多个表中，则需要在该变量前加上表明的前缀，来指定其表名；
• 若用户需要连接多个表，则需在from子句中加上多了表名，并用逗号隔开；

  proc sql;
      select salcomp.empid, lastname,
                 newsals.salary,mewsalay
      from sasuser.salcomps, sasuser.newsals
      where salcomps.empid=newsals.empid
      order by lastname;

七、Summarizing Groups of Data

       If you specify a GROUP BY clause in a query that does not contain a summary function, your clause is changed to an ORDER BY clause, and a message to the effect is written to the SAS log.

proc sql;
    select membertype 
              sum(milestraveled) as TotalMiles
     from sasuser.frequentflyer
    group by membertype;
/*输出每个membertype的milestraveled的和*/

八、HAVING语句：在含有GROUP BY子句的PROC SQL中筛选行

    A HAVING clause works with the GROUP BY clause to restrict the groups that are displayed in the output,based one or more specified conditions.

proc sql;
    select jobcode, avg(salary) as Avg
         from sasuser.payrollmaster
         group by jobcode
         having avy(salary)>40000
         order by jobcode;