Lesson 1 : PROC SQL Tutorial for Beginners (20 Examples)

This tutorial is designed for beginners who want to get started with PROC SQL. Also, it will attempt to compare the techniques of DATA Step and PROC SQL.

TERMINOLOGY
The difference between SAS and SQL terminology is shown in the table below.

SAS vs. SQL

SYNTAX

PROC SQL;

 SELECT column(s)

 FROM table(s) | view(s)

 WHERE expression

 GROUP BY column(s)

 HAVING expression

 ORDER BY column(s);

QUIT;

The SELECT statement must be specified in the following order: 

1.SELECT 

2.FROM 

3.WHERE 

4.GROUP BY 

5.HAVING 

6.ORDER BY 

Note:  Only the SELECT and FROM clauses are required. All the other clauses are optional.

Tip to Memorize SQL Query Order

EXPLANATION

PROC SQL: calls the SQL procedure
SELECT: specifies the column(s) (variables) to be selected
FROM: specifies the table(s) (data sets) to be queried
WHERE: subsets the data based on a condition
GROUP BY: classifies the data into groups based on the specified column(s)
ORDER BY: sorts the resulting rows (observations) by the specified column(s)
QUIT: ends the PROC SQL procedure

We are going to look at the difference between Non-SQL Base SAS and PROC SQL.

SAS Functions & Procedures vs SQL Statements & Clauses

Important Terminology

You would hear the word 'schema' from SQL programmers. It refers to design of database. In other words, it is the framework of database.

Prepare Dummy Data for Illustration
In the SAS program below, mylib is a name of permanent library which we are creating. Make sure you change the directory location of libname. We are using a sample of dataset which is stored in SASHELP library. This data set contains birth weight data.

libname mylib '/home/deepanshu/';

data mylib.outdata ;
 set SASHELP.BWEIGHT (obs=1000);
run;

PROC SQL STATEMENTS
1. Selecting all variables from the data set

proc sql; select * from mylib.outdata; Quit;

Asterisk (*) is used to select all columns (variables) in the order in which they are stored in the table.
Outdata is the table (data set) from which we need to select the columns (variables) . It is stored in MYLIB library.

To display the list of columns to the SAS log, use FEEDBACK option in the PROC SQL statement

proc sql feedback; select * from mylib.outdata; Quit;

The SAS log is shown below:

 71         proc sql feedback;
 72          select *
 73          from mylib.outdata;
 NOTE: Statement transforms to:
 
         select OUTDATA.Weight, OUTDATA.Black, OUTDATA.Married, OUTDATA.Boy, OUTDATA.MomAge, OUTDATA.MomSmoke, OUTDATA.CigsPerDay, 
 OUTDATA.MomWtGain, OUTDATA.Visit, OUTDATA.MomEdLevel
           from MYLIB.OUTDATA;
 
 74         Quit;

2. Selecting specific variables from the data set
In the SELECT clause, multiple columns are separated by commas.

proc sql; select weight,married from mylib.outdata; Quit;

In the SELECT clause, Weight and Married columns (variables) are specified so that we can select them from OUTDATA table (data set).


3. Limiting the number of rows
Suppose you want to limit the number of rows (observations) that PROC SQL displays, use the OUTOBS= option in the PROC SQL statement.

proc sql outobs=50; select weight,married from mylib.outdata; Quit;

4. Renaming a variable in output 
Suppose you want to rename a variable, use the column alias AS option in the PROC SQL statement.

options nolabel; proc sql; select weight,married as marriage from mylib.outdata; Quit;

The variable name has been renamed from married to marriage. options nolabel tells SAS not to use variable labels in SAS procedures. I used it so that you can see variable name has been changed to marriagae


5. Creating a new variable

Suppose you want to create a new variable that contains calculation.

proc sql; select weight, (weight*0.5) as newweight from mylib.outdata; Quit;

A new variable has been created and named newweight which is calculated on the basis of the existing variable weight.

6. Referring to a previously calculated variable
The keyword CALCULATED is used to refer a previously calculated variable.

proc sql; select weight, (weight*0.5) as newweight, CALCULATED newweight*0.25 as revweight from mylib.outdata; Quit;

7. Removing duplicate rows
The keyword DISTINCT is used to eliminate duplicate rows (observations) from your query results.

In the following program, we are asking SAS to remove all those cases where in duplicates exist on combination of both the variables - weight and married.

proc sql;
select DISTINCT weight, married 
from mylib.outdata;
quit; 

The DISTINCT * implies cases having same values in all the variables as a whole would be removed.

proc sql;
select DISTINCT *
from mylib.outdata;
quit; 

8. Labeling and formatting variables
SAS-defined formats can be used to improve the appearance of the body of a report. You can also label the variables using LABEL keyword.

options label; proc sql; select weight FORMAT= 8.2 , married Label =" Married People" from mylib.outdata; Quit;

9. Sorting data The ORDER BY clause returns the data in sorted order.

ASC option is used to sort the data in ascending order. It is the default option.
DESC option is used to sort the data in descending order

proc sql; select MoMAge, eight, married from mylib.outdata ORDER BY weight ASC, married DESC; Quit;

10. Subsetting data with the WHERE clause
Use the WHERE clause with any valid SAS expression to subset data.

List of conditional operators :
1. BETWEEN-AND
The BETWEEN-AND operator selects within an inclusive range of  values.

Example : where salary between 4500 and 6000;

2. CONTAINS or ?
The CONTAINS or ? operator  selects observations by searching for a specified set of characters within the values of a character variable

Example : where firstname contains ’DE’;
OR   where firstname ? ’DE’;

3. IN
The IN operator selects from a list of fixed values.

Example : where state = 'NC' or state = 'TX';

The easier way to write the above statement would be to use the IN operator

where state IN ('NC','TX');

4. IS MISSING or IS NULL
The IS MISSING or IS NULL operator selects missing values.

Example : where dateofbirth is missing

OR  where dateofbirth is null

5. LIKE

The LIKE Operator is used to select a pattern.

Important Point :
The WHERE clause can reference a previously calculated variable in two ways-
1. Use CALCULATED keyword.
2. Repeat the calculation in the WHERE clause.

Method I :

PROC SQL;
 SELECT momage,
 (WEIGHT * .01) AS NEWWEIGHT
 FROM mylib.outdata
 WHERE CALCULATED NEWWEIGHT > 5;
QUIT;

Method II :

PROC SQL;
 SELECT momage, (WEIGHT * .01) AS NEWWEIGHT
 FROM mylib.outdata
 WHERE (WEIGHT * .01) > 5;
QUIT;

11. Multiple Conditions / Criteria

PROC SQL; SELECT WEIGHT, CASE WHEN WEIGHT BETWEEN 0 AND 2000 THEN 'LOW' WHEN WEIGHT BETWEEN 2001 AND 3000 THEN 'MEDIUM' WHEN WEIGHT BETWEEN 3001 AND 4000 THEN 'HIGH' ELSE 'VERY HIGH' END AS NEWWEIGHT FROM mylib.outdata; QUIT;
The END is required when using the CASE.

The following operators can be used in CASE expression:
• All operators that IF uses (= , <, >, NOT, NE, AND, OR, IN, etc)
• BETWEEN AND
• CONTAINS or ‘?’
• IS NULL or IS MISSING
• = *
• LIKE

12. Aggregating or summarizing data

Use GROUP BY clause to summarize data. Summary functions are used on the SELECT statement to produce summary for each of the analysis variables.

proc sql; select momage, COUNT(married) AS marriage from mylib.outdata GROUP BY momage; Quit;

The summary functions available are listed below:

1. AVG/MEAN
2. COUNT/FREQ/N 
3. SUM
4. MAX 
5. MIN 
6. NMISS 
7. STD 
8. VAR
9. T (t value)
10. USS (Uncorrelated Sum of Square)
11. CSS (Correlated Sum of Square)
12. RANGE

13. Subsetting data in the groups
In order to subset data when grouping is in effect, the HAVING clause must be used. The variable specified in having clause must contain summary statistics.

proc sql; select momage, weight, COUNT(married) AS marriage from mylib.outdata GROUP BY momage, weight HAVING marriage > 2; Quit;

Important Point -

The WHERE clause cannot be used to subset aggregated data. To subset data with the GROUP BY clause you must use HAVING clause.

14. Creating a new data set as output

The CREATE TABLE statement can be used to create a new data set as output instead of a report produced in output window.

SYNTAX

PROC SQL;
 CREATE TABLE table-name AS
 SELECT column(s)
 FROM table(s) | view(s)
 WHERE expression
 GROUP BY column(s)
 ORDER BY column(s);
 QUIT; 

proc sql; create table health AS select weight, married from mylib.outdata ORDER BY weight ASC, married DESC; Quit;

15. Limiting the number of rows in the new created data set
Suppose you want to limit the number of rows (observations) that PROC SQL produces in the data set, use the INOBS= option in the PROC SQL statement.

proc sql INOBS=50; create table health AS select weight,married from mylib.outdata; Quit;

Difference between INOBS= and OUTOBS=
INOBS controls how many records are read from the dataset and OUTOBS controls how many records are written. Run the following program and see the difference. Both returns different results.

/* OUTOBS=Example*/
proc sql outobs=2;
select age, count(*) as tot
from sashelp.class
group by age;
quit;


/* INOBS= Example */
proc sql inobs=4;
select age, count(*) as tot
from sashelp.class
group by age;
quit;

16. Counting unique values by a grouping variable
Suppose you are asked to calculate the unique number of age values by Sex columns using SASHELP.CLASS dataset

You can use PROC SQL with COUNT(DISTINCT variable_name) to determine the number of unique values for a column.

PROC SQL;
CREATE TABLE TEST1 as
SELECT Sex,
Count(distinct Age) AS Unique_count
FROM sashelp.class
GROUP BY Sex;
QUIT;

17. Count the number of missing values

You can use NMISS() function to compute the number of missing values in a variable. The COUNT() function returns the number of non-missing values in a variable.

data temp;
input id;
cards;
1
2
.
4
5
.
;
run;

proc sql;
select nmiss(id) as N_missings,
count(id) as N,
calculated N_missings + calculated N as total
from temp;
quit;

Proc SQL : Number of Missing Values

How to refer to a calculated variable

The keyword CALCULATED is used to refer to a newly created variable for further calculation. In this case, we have used CALCULATED to sum 'N_MISSINGS' and 'N' variables.

18. KEEP and DROP some variables

Suppose you need to keep all the variables from SASHELP.CARS except variables 'MODEL' and 'MAKE'. The DROP= option is used to drop these two variables. Similarly, we can use KEEP= option to keep specific variables. These DROP= and KEEP= Options are not native SQL language. It only works in SAS.

proc sql;
create table saslearning (drop= make model) as
select * from sashelp.cars;
quit;

19. Delete Rows from a Table

You can use DELETE FROM  statement to remove records (rows) from a dataset.

proc sql;
delete from mylib.outdata
where momage > 0;
quit;

In this case, we are deleting all records having momage greater than 0 from outdata dataset. Log shows '478 rows were deleted from MYLIB.OUTDATA'.

20. Sub Query
Find employee IDs who have records in table file1 but not in table file2.

data file1;
input ID age;
cards;
1 24
2 34
3 45
4 67
;
run;

data file2;
input ID age;
cards;
1 25
3 46
4 62
;
run;

Proc SQL;
Select ID from file1
Where ID not in (select ID from file2);
Quit;

21. Sub Query - Part II
Find employee IDs whose age is in the average age +/- 10 years.

Proc SQL;
Select id from file1
where age between (select Avg(age) from file1) - 10 and
(select avg(age) from file1)+10;
Quit;

22. Sub Query - Part III

proc sql;
select Name, Grade, Teacher,
Case
When Student_ID in
(select Student_ID from Tests where Score lt 70) then 'Failed one or more tests'
else 'Passed all tests'
end as Test_Results
from Students;
quit;

Next Lesson : PROC SQL Joins

Proc SQL Tutorials : 15 Proc SQL Tutorials

SAS Tutorials : 100 Free SAS Tutorials

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About Author:

Deepanshu founded ListenData with a simple objective - Make analytics easy to understand and follow. He has over 10 years of experience in data science. During his tenure, he has worked with global clients in various domains like Banking, Insurance, Private Equity, Telecom and Human Resource.

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