Chapter Contents

Previous

Next

WHERE

Valid:	in DATA and PROC steps
Category:	Action
Type:	Declarative

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

General Information

Using the WHERE statement may 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. For more information about indexes, see "Indexes" in the "SAS Data Files" chapter 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.  

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 programming statements that select observations by observation number, such as the OBS= data set option and the POINT= option in the SET and MODIFY statements. When you use the WHERE statement, the FIRSTOBS= data set option must be 1. 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 CARDS or DATALINES statement.

For each iteration of the DATA step, the first operation the SAS System 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 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 for subsetting the original data set for processing by the procedure. The 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:

• the BETWEEN-AND operator

• the comparison operators, with or without the colon modifier

• the CONTAINS operator

• the IS NULL and IS NOT NULL operators

• the LIKE operator

• the TRIM function

• the SUBSTR function, in some cases.

SUBSTR requires the following arguments:

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

• position is equal to 1

• length is less than or equal to the length of variable

• length is equal to the length of character-string.

Operands Used in WHERE Expressions

Operands include

• constants

• time and date values

• values of variables that are obtained from the SAS data sets

• values created within the WHERE expression itself.

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.

Use operands in WHERE statements as in the following examples:

• where score>50;

• where date>='01jan87'd and time>='9:00't;

• where state='Mississippi';

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:

• where empnum;

• where 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 Processing" in SAS Language Reference: Concepts.

WHERE Statement Operators

Operator Type		Symbol or Mnemonic	Description
Arithmetic
		*	multiplication
		/	division
		+	addition
		-	subtraction
		**	exponentiation
Comparison
		= or EQ	equal to
		ˆ=, <>, or NE  (table note 1)	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 OR (table note 2)	logical or
		~,^ , ¬, or NOT (table note 3)	logical not
Other
		|| (table note 4)	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

The caret (^), tilde (~), and the not sign (¬ ) all indicate a logical not. Use the character available on your keyboard, or use the mnemonic equivalent. 

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.  

The caret (^), tilde (~), and the not sign (¬ ) all indicate a logical not. Use the character available on your keyboard, or use the mnemonic equivalent.  

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

You can use the colon modifier (:) with any of the comparison operators. See SAS Operators for more information about the colon modifier.

Comparisons

• You can use the WHERE command in SAS/FSP software to subset data for editing and browsing. You can use both the WHERE statement and WHERE= data set option in windowing procedures and in conjunction with the WHERE command.

• To select observations from individual data sets when a SET, MERGE, MODIFY, or UPDATE statement specifies more than one data set, apply a WHERE= data set option to each data set. In the DATA step, if a WHERE statement and a WHERE= data set option apply to the same data set, SAS uses the data set option and ignores the statement.

• The most important differences between the WHERE statement in the DATA step and the subsetting IF statement are as follows:
  • The WHERE statement selects observations before they are brought into the program data vector, making it a more efficient programming technique. The subsetting IF statement works on observations after they are read into the program data vector.

  • The WHERE statement can produce a different data set from the subsetting IF when a BY statement accompanies a SET, MERGE, or UPDATE statement. The different data set occurs because SAS creates BY groups before the subsetting IF statement selects but after the WHERE statement selects.

  • The WHERE statement cannot be executed conditionally as part of an IF statement, but the subsetting IF statement can.

  • The WHERE statement selects observations in SAS data sets only, whereas the subsetting IF statement selects observations from an existing SAS data set or from observations that are created with an INPUT statement.

  • The subsetting IF statement cannot be used in SAS windowing procedures to subset observations for browsing or editing.

• Do not confuse the WHERE statement with the DROP or KEEP statement. The DROP and KEEP statements select variables for processing. The WHERE statement selects observations.

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

• Using BETWEEN-AND:

  
  where empnum between 500 and 1000;

• Using CONTAINS:

  
  where company ? 'bay';
  where company contains 'bay';

• Using IS NULL and IS MISSING:

  
  where name is null;
  where name is missing;

• Using LIKE to select all names that start with the letter D:

  
  where name like 'D%';

• Using LIKE to match patterns from a list of the following names:

  	Diana
  	Diane
  	Dianna
  	Dianthus
  	Dyan

  WHERE Statement	Name Selected
  where name like 'D_an';	Dyan
  where name like 'D_an_';	Diana, Diane
  where name like 'D_an__';	Dianna
  where name like 'D_an%';	all names from list

  
  

• Using the Sounds-like Operator to select names that sound like "Smith":

  
  where lastname=*'Smith';

• Using SAME-AND:

  
  where year>1981;
  . . . more SAS statements . . .
  where same and year<1986;

  In this example, the second WHERE statement is equivalent to the following WHERE statement:

  
  where year>1981 and year<1986;

See Also

	Statement: IF, Subsetting
	Data Set Option: WHERE=
	SAS Guide to the SQL Procedure: Usage and Reference
	SAS/IML Software: Usage and Reference, Version 6, First Edition
	SAS Procedures Guide
	SAS Indexes in SAS Language Reference: Concepts
	WHERE 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.

Chapter Contents

Previous

Next

Top of Page

Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.