SAS 9.1 SQL教程：初学者指南

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"SAS Base SQL Procedure（SAS SQL语言）" SAS SQL语言是SAS编程环境中的一个强大工具，用于数据管理和分析。它基于标准的SQL（结构化查询语言），但添加了一些特定于SAS的功能，使得在SAS环境中处理数据变得更加高效和灵活。SAS 9.1 SQL Procedure User's Guide是学习和理解SAS SQL的一个重要参考资料，它为初学者提供了清晰的指导，包括实际操作实例，帮助用户快速上手。该指南由SAS Institute Inc.于2004年出版，包含了SAS SQL的所有基本概念、语法和高级特性。通过学习此教程，用户可以掌握如何使用SQL在SAS环境中进行数据查询、数据操纵、数据聚合以及报告生成等任务。以下是SAS SQL的一些关键知识点： 1. **数据集操作**：SAS SQL允许用户创建、修改和删除数据集。例如，使用`CREATE TABLE`语句创建新数据集，`INSERT INTO`语句向数据集中添加记录，`UPDATE`语句修改现有记录，以及`DELETE`语句删除指定记录。 2. **查询与联接**：SAS SQL支持多表查询，通过`JOIN`操作（如INNER JOIN、LEFT JOIN、RIGHT JOIN和FULL JOIN）来合并来自多个数据集的信息。此外，`SELECT`语句用于选择需要的字段，并可配合`WHERE`子句进行条件过滤。 3. **聚合函数**：SAS SQL提供了诸如`SUM`、`AVG`、`MAX`、`MIN`等聚合函数，用于计算总和、平均值、最大值和最小值。`GROUP BY`语句用于按指定字段对数据进行分组，`HAVING`语句则在分组后进行条件筛选。 4. **窗口函数**：SAS SQL支持窗口函数，如`LAG`、`LEAD`、`RANK`、`ROW_NUMBER`等，它们在处理时间序列数据或需要计算排名和差异时非常有用。 5. **子查询**：嵌套查询是SQL中的一个重要概念，SAS SQL也支持子查询，可以在主查询中嵌入一个或多个查询，以实现更复杂的逻辑。 6. **数据转换**：SAS SQL提供了丰富的数据类型和转换功能，如日期和时间处理、字符数据的处理等，允许用户根据需要转换和清洗数据。 7. **过程调用**：SAS SQL可以与其他SAS过程（如PROC SORT、PROC FORMAT等）结合使用，以实现更复杂的处理流程。 8. **程序控制**：除了基本的SQL语句，SAS SQL还包含一些程序控制结构，如`IF-THEN-ELSE`和`CASE`语句，使用户能够在SQL代码中实现条件逻辑。 9. **性能优化**：SAS SQL提供了索引、分区、并行处理等机制来优化查询性能，尤其是在处理大型数据集时。 SAS 9.1 SQL Procedure User's Guide不仅涵盖了以上所有知识点，还可能包含更多实用技巧和最佳实践，是SAS SQL学习者和使用者的重要参考文献。通过深入学习并实践其中的例子，用户可以熟练掌握SAS SQL，从而更好地利用SAS进行数据分析和决策支持。

12 Overview of the SELECT Statement

Chapter 2

Using a WHERE Clause with Missing Values

Summarizing Data

Using Aggregate Functions

Summarizing Data with a WHERE Clause

Using the MEAN Function with a WHERE Clause

Displaying Sums

Combining Data from Multiple Rows into a Single Row

Remerging Summary Statistics

Using Aggregate Functions with Unique Values

Counting Unique Values

Counting Nonmissing Values

Counting All Rows

Summarizing Data with Missing Values

Finding Errors Caused by Missing Values

Grouping Data

Grouping by One Column

Grouping without Summarizing

Grouping by Multiple Columns

Grouping and Sorting Data

Grouping with Missing Values

Finding Grouping Errors Caused by Missing Values

Filtering Grouped Data

Using a Simple HAVING Clause

Choosing Between HAVING and WHERE

Using HAVING with Aggregate Functions

Validating a Query

Overview of the SELECT Statement

This chapter shows you how to

retrieve data from a single table by using the SELECT statement

validate the correctness of a SELECT statement by using the VALIDATE

statement.

With the SELECT statement, you can retrieve data from tables or data that is

described by SAS data views.

Note: The examples in this chapter retrieve data from tables that are SAS data

sets. However, you can use all of the operations that are described here with SAS data

views.

The SELECT statement is the primary tool of PROC SQL. You use it to identify,

retrieve, and manipulate columns of data from a table. You can also use several

optional clauses within the SELECT statement to place restrictions on a query.

SELECT and FROM Clauses

The following simple SELECT statement is sufﬁcient to produce a useful result:

select Name

from sql.countries;

The SELECT statement must contain a SELECT clause and a FROM clause, both of

which are required in a PROC SQL query. This SELECT statement contains

Retrieving Data from a Single Table

Overview of the SELECT Statement 13

a SELECT clause that lists the Name column

a FROM clause that lists the table in which the Name column resides.

WHERE Clause

The WHERE clause enables you to restrict the data that you retrieve by specifying a

condition that each row of the table must satisfy. PROC SQL output includes only those

rows that satisfy the condition. The following SELECT statement contains a WHERE

clause that restricts the query output to only those countries that have a population

that is greater than 5,000,000 people:

select Name

from sql.countries

where Population gt 5000000;

ORDER BY Clause

The ORDER BY clause enables you to sort the output from a table by one or more

columns; that is, you can put character values in either ascending or descending

alphabetical order, and you can put numerical values in either ascending or descending

numerical order. The default order is ascending. For example, you can modify the

previous example to list the data by descending population:

select Name

from sql.countries

where Population gt 5000000

order by Population desc;

GROUP BY Clause

The GROUP BY clause enables you to break query results into subsets of rows.

When you use the GROUP BY clause, you use an aggregate function in the SELECT

clause or a HAVING clause to instruct PROC SQL how to group the data. For details

about aggregate functions, see “Summarizing Data” on page 39. PROC SQL calculates

the aggregate function separately for each group. When you do not use an aggregate

function, PROC SQL treats the GROUP BY clause as if it were an ORDER BY clause,

and any aggregate functions are applied to the entire table.

The following query uses the SUM function to list the total population of each

continent. The GROUP BY clause groups the countries by continent, and the ORDER

BY clause puts the continents in alphabetical order:

select Continent, sum(Population)

from sql.countries

group by Continent

order by Continent;

HAVING Clause

The HAVING clause works with the GROUP BY clause to restrict the groups in a

query’s results based on a given condition. PROC SQL applies the HAVING condition

after grouping the data and applying aggregate functions. For example, the following

query restricts the groups to include only the continents of Asia and Europe:

select Continent, sum(Population)

from sql.countries

group by Continent

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