Previous Page | Next Page

Statements

WHERE Statement



Selects observations from SAS data sets that meet a particular condition.
Valid: in DATA and PROC steps
Category: Action
Type: Declarative

Syntax
Arguments
Details
The Basics
In DATA Steps
WHERE and BY in a DATA Step
In PROC Steps
Use of Indexes
Operands Used in WHERE Expressions
Operators Used in the WHERE Expression
Comparisons
Examples
Example 1: Basic WHERE Statement Usage
Example 2: Using Operators Available Only in the WHERE Statement
See Also

Syntax

WHERE where-expression-1
< logical-operator where-expression-n>;


Arguments

where-expression

is an arithmetic or logical expression that generally consists of a sequence of operands and operators.

Tip: The operands and operators described in the next several sections are also valid for the WHERE= data set option.
Tip: You can specify multiple where-expressions.
logical-operator

can be AND, AND NOT, OR, or OR NOT.


Details


The Basics

Using the WHERE statement might improve the efficiency of your SAS programs because SAS is not required to read all observations from the input data set.

The WHERE statement cannot be executed conditionally. That is, you cannot use it as part of an IF-THEN statement.

WHERE statements can contain multiple WHERE expressions that are joined by logical operators.

Note:   Using indexed SAS data sets can significantly improve performance when you use WHERE expressions to access a subset of the observations in a SAS data set. See Understanding SAS Indexes in the "SAS Data Files" section of SAS Language Reference: Concepts for a complete discussion of WHERE-expression processing with indexed data sets and a list of guidelines to consider before you index your SAS data sets.  [cautionend]


In DATA Steps

The WHERE statement applies to all data sets in the preceding SET, MERGE, MODIFY, or UPDATE statement, and variables that are used in the WHERE statement must appear in all of those data sets. You cannot use the WHERE statement with the POINT= option in the SET and MODIFY statements.

You can apply OBS= and FIRSTOBS= processing to WHERE processing. For more information, see Processing a Segment of Data That is Conditionally Selected in the "WHERE-Expression Processing" section of SAS Language Reference: Concepts.

You cannot use the WHERE statement to select records from an external file that contains raw data, nor can you use the WHERE statement within the same DATA step in which you read in-stream data with a DATALINES statement.

For each iteration of the DATA step, the first operation SAS performs in each execution of a SET, MERGE, MODIFY, or UPDATE statement is to determine whether the observation in the input data set meets the condition of the WHERE statement. The WHERE statement takes effect immediately after the input data set options are applied and before any other statement in the DATA step is executed. If a DATA step combines observations using a WHERE statement with a MERGE, MODIFY, or UPDATE statement, SAS selects observations from each input data set before it combines them.


WHERE and BY in a DATA Step

If a DATA step contains both a WHERE statement and a BY statement, the WHERE statement executes before BY groups are created. Therefore, BY groups reflect groups of observations in the subset of observations that are selected by the WHERE statement, not the actual BY groups of observations in the original input data set.

For a complete discussion of BY-group processing, see BY-Group Processing in SAS Programs in SAS Language Reference: Concepts.


In PROC Steps

You can use the WHERE statement with any SAS procedure that reads a SAS data set. The WHERE statement is useful in order to subset the original data set for processing by the procedure. The Base SAS Procedures Guide documents the action of the WHERE statement only in those procedures for which you can specify more than one data set. In all other cases, the WHERE statement performs as documented here.


Use of Indexes

A DATA or PROC step attempts to use an available index to optimize the selection of data when an indexed variable is used in combination with one of the following operators and functions:

SUBSTR requires the following arguments:

where substr(variable,position,length)
 ='character-string';

An index is used in processing when the arguments of the SUBSTR function meet all of the following conditions:


Operands Used in WHERE Expressions

Operands in WHERE expressions can contain the following values:

You cannot use variables that are created within the DATA step (for example, FIRST.variable, LAST.variable, _N_, or variables that are created in assignment statements) in a WHERE expression because the WHERE statement is executed before the SAS System brings observations into the DATA or PROC step. When WHERE expressions contain comparisons, the unformatted values of variables are compared.

The following are examples of using operands in WHERE expressions:

As in other SAS expressions, the names of numeric variables can stand alone. SAS treats values of 0 or missing as false; other values are true. These examples are WHERE expressions that contain the numeric variables EMPNUM and SSN:

Character literals or the names of character variables can also stand alone in WHERE expressions. If you use the name of a character variable by itself as a WHERE expression, SAS selects observations where the value of the character variable is not blank.


Operators Used in the WHERE Expression

You can include both SAS operators and special WHERE-expression operators in the WHERE statement. For a complete list of the operators, see WHERE Statement Operators. For the rules SAS follows when it evaluates WHERE expressions, see WHERE-Expression Processing in SAS Language Reference: Concepts.

WHERE Statement Operators
Operator Type Symbol or Mnemonic Description
Arithmetic


* multiplication

/ division

+ addition

- subtraction

** exponentiation
Comparison 4


= or EQ equal to

^=, ¬=, ~=, or NE1 not equal to

> or GT greater than

< or LT less than

>= or GE greater than or equal to

<= or LE less than or equal to

IN equal to one of a list
Logical (Boolean)


& or AND logical and

| or OR2 logical or1

~,^ , ¬, or NOT1 logical not
Other


||3 concatenation of character variables

( ) indicate order of evaluation

+ prefix positive number

- prefix negative number
WHERE Expression Only


BETWEEN-AND an inclusive range

? or CONTAINS a character string

IS NULL or IS MISSING missing values

LIKE match patterns

=* sounds-like

SAME-AND add clauses to an existing WHERE statement without retyping original one
1 The caret (^), tilde (~), and the not sign (¬ ) all indicate a logical not. Use the character available on your keyboard, or use the mnemonic equivalent.

2 The OR symbol ( | ), broken vertical bar ( | ), and exclamation point (!) all indicate a logical or. Use the character available on your keyboard, or use the mnemonic equivalent.

3 Two OR symbols (| | ), two broken vertical bars ( | | ), or two exclamation points (!!) indicate concatenation. Use the character available on your keyboard.

4 You can use the colon modifier (:) with any of the comparison operators in order to compare only a specified prefix of a character string.


Comparisons


Examples


Example 1: Basic WHERE Statement Usage

This DATA step produces a SAS data set that contains only observations from data set CUSTOMER in which the value for NAME begins with Mac and the value for CITY is Charleston or Atlanta .

data testmacs;
   set customer;
   where substr(name,1,3)='Mac' and
         (city='Charleston' or city='Atlanta');
run;


Example 2: Using Operators Available Only in the WHERE Statement


See Also

Data Set Option:

WHERE= Data Set Option

Statement:

IF Statement, Subsetting

SAS SQL Query Window User's Guide

SAS/IML User's Guide

Base SAS Procedures Guide

"SAS Indexes" in SAS Language Reference: Concepts

"WHERE-Expression Processing" in SAS Language Reference: Concepts

"BY-Group Processing" in SAS Language Reference: Concepts

Beatrous, S. & Clifford, W. (1998), "Sometimes You Do Get What You Want: SAS I/O Enhancements in Version 7," Proceedings of the Twenty-third Annual SAS Users Group International Conference, 23.

Previous Page | Next Page | Top of Page