Ask the Expert - Sas Institute...To understand how SQL processes a join, it is important to...

Copyright © SAS Inst itute Inc. A l l r ights reserved.

Ask the ExpertSAS SQL: An Introduction


Ask the ExpertSAS SQL: An Introduction

Presenter

Cynthia JohnsonSenior Systems Engineer, SAS Customer Loyalty Team


The SQL Procedure

The SQL procedure: enables the use of SQL in SAS

is part of Base SAS software

follows American National Standards Institute (ANSI) standards

includes enhancements for compatibility with SAS software


The SQL Procedure

The SQL procedure is a tool for querying data

a tool for data manipulation and management

an augmentation to the DATA step.

The SQL procedure is not a DATA step replacement

a custom reporting tool.


Structured Query Language

Input Output

PROC

SQL

Report

PROC SQL

SAS Data Set

SAS Data View

SAS Data Set

SAS Data View

DBMS Table

DBMS Table


SELECT Statement Syntax

General form of the SELECT statement with selected clauses:

SELECT column-1<, ...column-n>

FROM table-1|view-1<, ...table-n|view-n>

<WHERE expression>

<GROUP BY column-1<, …column-n>>

<HAVING expression>

<ORDER BY column-1<DESC><, …column-n>>;


Select Statement Syntax

To help you remember…

So

Few

Workers

Go

Home

On time;


SELECT Statement Syntax

Order of execution for SQL clauses:

5 SELECT column-1<, ...column-n>

1 FROM table-1|view-1<, ...table-n|view-n>

2 <WHERE expression>

3 <GROUP BY column-1<, …column-n>>

4 <HAVING expression>

6 <ORDER BY column-1<DESC><, …column-n>>;


Order of Execution

• The FROM clause is processed first. This clause identifies the data sets from which SQL is reading

• The WHERE clause is a pre-processor. As with the DATA step, the WHERE clause searches the original data set(s) for values that meet the WHERE condition. These results are stored in an intermediate table.

• The GROUP BY is the next clause that processes. The GROUP BY clause creates groupings within the data.


Order of Execution

• The HAVING clause is processed next. This clause subsets based upon groups that were created by the GROUP BY clause. It also builds an intermediate table.

• The SELECT clause selects the columns for the results set.

• The ORDER BY clause orders (or sorts) the rows.


Demonstration

Let’s use SQL to query and manipulate a data set.


Combining Data from Multiple Tables

SQL uses joins to combine tables horizontally.

Table A Table B


Types of Joins

PROC SQL supports two types of joins: inner joins

outer joins


Inner JoinsInner joins return only matching rows

enable a maximum of 256 tables to be joined at the same time.


Types of Joins

Outer joins return all matching rows, plus nonmatching rows

from one or both tables can be performed on only two tables or views

at a time.

Full RightLeft


Cartesian Product

To understand how SQL processes a join, it is important to understand the concept of the Cartesian product.

A query that lists multiple tables in the FROM clause without a WHERE clause produces all possible combinations of rows from all tables. This result is called the Cartesian product.

select *from one, two;


Cartesian Product

Table OneX A

1 a

4 d

2 b

Table TwoX B

2 x

3 y

5 v


Cartesian Product

Table OneX A

1 a

4 d

2 b

Table TwoX B

2 x

3 y

5 v

Result SetX A X B

1 a 2 x

1 a 3 y

1 a 5 v

4 d 2 x

4 d 3 y

4 d 5 v

2 b 2 x

2 b 3 y

2 b 5 v


Demonstration

Write a query that performs an inner join.


Outer Joins

Full Join Retrieve the matching rows as well as the non-matches from the left table and

the non-matches from the right table.

Full


Full Join

select * from one full join two

on one.x = two.x;

Table OneX A

1 a

4 d

2 b

Table TwoX B

2 x

3 y

5 v

X A X B

1 a .

2 b 2 x

. 3 y

4 d .

. 5 v


SQL Full Join

SQL joins do not automatically overlay same-named columns.

Table One

b2d4a1

AX

Table Two

v5y3x2

BX

proc sql;select one.x, a, b

from one full join twoon one.x=two.x

;quit;

X A B1 a2 b x

y4 d

v

Output


The COALESCE Function

The COALESCE function returns the value of the first non-missing argument.

General form of the COALESCE function:COALESCE(argument-1,argument-2<, ...argument-n)


SQL Full Join

You can use the COALESCE function to overlay columns.

Table One

b2d4a1

AX

Table Two

v5y3x2

BX

proc sql;select

coalesce(one.x,two.x)as x,a,b

from one full join twoon one.x=two.x;

quit;

Output

X A B1 a2 b x3 y4 d5 v


SQL Join versus DATA Step Merge

The DATA step code producing similar results:

Table One

b2d4a1

AX

Table Two

v5y3x2

BX

proc sort data=one;

by x;

run;

data three;

merge one two;

by x;

run;

Output


SQL Join versus DATA Step Merge

Key Points SQL Join DATA Step

Merge

Explicit sorting of data

before join/merge

Not required Required

Same-named columns in

join/merge expressions


Equality in join or merge

expressions



PROC SQL and Macro Variables

PROC SQL creates or updates macro variables using an INTO clause.

The INTO clause has varied syntaxes, and each produces a different result.


PROC SQL and Macro Variables

The following syntax places values from the first row returned by an SQL query into macro variable(s). Data from additional rows returned by the query is ignored.

General form of the SELECT statement with an INTO clause:

The value from the first column in the SELECT list is placed in the first macro variable listed in the INTO clause, and so on.

SELECT column-1<, …column-n>

INTO :macvar_1<, ... :macvar_n>

FROM table|view …


Demonstration

Create macro variables with PROC SQL.


support.sas.com Resources

• SAS ® Base SAS Documentation

http://support.sas.com/documentation/onlinedoc/base/index.html

• Papers & SAS Notes

http://support.sas.com/resources/papers/sgf09/336-2009.pdf

http://support.sas.com/kb/20/783.html

• SAS Training

https://support.sas.com/edu/schedules.html?ctry=us&id=2579

http://support.sas.com/documentation/onlinedoc/base/index.html

http://support.sas.com/resources/papers/sgf09/336-2009.pdf

http://support.sas.com/kb/20/783.html

https://support.sas.com/edu/schedules.html?ctry=us&id=2579


support.sas.com Resources

• Support Communities

https://communities.sas.com/

• Blogs

http://blogs.sas.com/content/

https://communities.sas.com/


sas.com


Thank you for attending!

http://www.sas.com/


Q&APlease submit your questions in the Q&A window


@SASSoftware

SASSoftware

communities.sas.com

SAS Software, SASUsersgroup

SAS, SAS Users Group

blogs.sas.com/content

http://twitter.com/sassoftware

http://www.youtube.com/sassoftware

http://communities.sas.com/

https://www.facebook.com/SASsoftware/

https://www.facebook.com/SASUsersgroup

https://www.linkedin.com/company/sas

https://www.linkedin.com/groups/4000846



Learn SAS with SAS Education

SAS Education will support you in continual learning to grow your career.

• SAS Training Coursessupport.sas.com/training

• Get SAS Certifiedsupport.sas.com/certify

• SAS Bookssupport.sas.com/books

Contact SAS Training Customer Service(800) 727-0025 or [email protected] your webinar host, Rochelle Whittle at (919) 531-3090

http://support.sas.com/training

http://support.sas.com/certify/index.html

http://support.sas.com/publishing/index.html

mailto:[email protected]


Ask the ExpertFeedback

Please fill out survey as you leave WebEx today.

Thank you for joining us today!

Ask the Expert - Sas Institute...To understand how SQL processes a join, it is important to...

Documents

Transcript of Ask the Expert - Sas Institute...To understand how SQL processes a join, it is important to...