Expressions

An expression is an arbitrarily complex combination of variables, constants, literals, operators, and function calls. The simplest expression is a single variable.

The PL/SQL compiler determines the datatype of an expression from the types of the variables, constants, literals, and operators that comprise the expression. Every time the expression is evaluated, a single value of that type results. For more information, see "PL/SQL Expressions and Comparisons".

Syntax

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Keyword and Parameter Description

BETWEEN

This comparison operator tests whether a value lies in a specified range. It means "greater than or equal to low value and less than or equal to high value."

boolean_constant_name

This identifies a constant of type BOOLEAN, which must be initialized to the value TRUE, FALSE, or NULL. Arithmetic operations on Boolean constants are not allowed.

boolean_expression

This is an expression that yields the Boolean value TRUE, FALSE, or NULL.

boolean_function_call

This is any function call that returns a Boolean value.

boolean_literal

This is the predefined value TRUE, FALSE, or NULL (which stands for a missing, unknown, or inapplicable value). You cannot insert the value TRUE or FALSE into a database column.

boolean_variable_name

This identifies a variable of type BOOLEAN. Only the values TRUE, FALSE, and NULL can be assigned to a BOOLEAN variable. You cannot select or fetch column values into a BOOLEAN variable. Also, arithmetic operations on BOOLEAN variables are not allowed.

%BULK_ROWCOUNT

Designed for use with the FORALL statement, this is a composite attribute of the implicit cursor SQL. For more information, see "SQL Cursor".

character_constant_name

This identifies a previously declared constant that stores a character value. It must be initialized to a character value or a value implicitly convertible to a character value.

character_expression

This is an expression that yields a character or character string.

character_function_call

This is a function call that returns a character value or a value implicitly convertible to a character value.

character_literal

This is a literal that represents a character value or a value implicitly convertible to a character value.

character_variable_name

This identifies a previously declared variable that stores a character value.

collection_name

This identifies a collection (nested table, index-by table, or varray) previously declared within the current scope.

cursor_name

This identifies an explicit cursor previously declared within the current scope.

cursor_variable_name

This identifies a PL/SQL cursor variable previously declared within the current scope.

date_constant_name

This identifies a previously declared constant that stores a date value. It must be initialized to a date value or a value implicitly convertible to a date value.

date_expression

This is an expression that yields a date/time value.

date_function_call

This is a function call that returns a date value or a value implicitly convertible to a date value.

date_literal

This is a literal that represents a date value or a value implicitly convertible to a date value.

date_variable_name

This identifies a previously declared variable that stores a date value.

EXISTS, COUNT, FIRST, LAST, LIMIT, NEXT, PRIOR

These are collection methods. When appended to the name of a collection, these methods return useful information. For example, EXISTS(n) returns TRUE if the nth element of a collection exists. Otherwise, EXISTS(n) returns FALSE. For more information, see "Collection Methods".

exponent

This is an expression that must yield a numeric value.

%FOUND, %ISOPEN, %NOTFOUND, %ROWCOUNT

These are cursor attributes. When appended to the name of a cursor or cursor variable, these attributes return useful information about the execution of a multi-row query. You can also append them to the implicit cursor SQL.

host_cursor_variable_name

This identifies a cursor variable declared in a PL/SQL host environment and passed to PL/SQL as a bind variable. Host cursor variables must be prefixed with a colon.

host_variable_name

This identifies a variable declared in a PL/SQL host environment and passed to PL/SQL as a bind variable. The datatype of the host variable must be implicitly convertible to the appropriate PL/SQL datatype. Also, host variables must be prefixed with a colon.

IN

This comparison operator tests set membership. It means "equal to any member of." The set can contain nulls, but they are ignored. Also, expressions of the form

value NOT IN set

yield FALSE if the set contains a null.

index

This is a numeric expression that must yield a value of type BINARY_INTEGER or a value implicitly convertible to that datatype.

indicator_name

This identifies an indicator variable declared in a PL/SQL host environment and passed to PL/SQL. Indicator variables must be prefixed with a colon. An indicator variable "indicates" the value or condition of its associated host variable. For example, in the Oracle Precompiler environment, indicator variables can detect nulls or truncated values in output host variables.

IS NULL

This comparison operator returns the Boolean value TRUE if its operand is null, or FALSE if its operand is not null.

LIKE

This comparison operator compares a character value to a pattern. Case is significant. LIKE returns the Boolean value TRUE if the character patterns match, or FALSE if they do not match.

NOT, AND, OR

These are logical operators, which follow the tri-state logic of Table 2-2. AND returns the value TRUE only if both its operands are true. OR returns the value TRUE if either of its operands is true. NOT returns the opposite value (logical negation) of its operand. For more information, see "Logical Operators".

NULL

This keyword represents a null; it stands for a missing, unknown, or inapplicable value. When NULL is used in a numeric or date expression, the result is a null.

numeric_constant_name

This identifies a previously declared constant that stores a numeric value. It must be initialized to a numeric value or a value implicitly convertible to a numeric value.

numeric_expression

This is an expression that yields an integer or real value.

numeric_function_call

This is a function call that returns a numeric value or a value implicitly convertible to a numeric value.

numeric_literal

This is a literal that represents a number or a value implicitly convertible to a number.

numeric_variable_name

This identifies a previously declared variable that stores a numeric value.

pattern

This is a character string compared by the LIKE operator to a specified string value. It can include two special-purpose characters called wildcards. An underscore (_) matches exactly one character; a percent sign (%) matches zero or more characters.

relational_operator

This operator lets you compare expressions. For the meaning of each operator, see "Comparison Operators".

SQL

This identifies a cursor opened implicitly by Oracle to process a SQL data manipulation statement. The implicit cursor SQL always refers to the most recently executed SQL statement.

+, -, /, *, **

These symbols are the addition, subtraction, division, multiplication, and exponentiation operators, respectively.

||

This is the concatenation operator. As the following example shows, the result of concatenating string1 with string2 is a character string that contains string1 followed by string2:

'Good' || ' morning!' = 'Good morning!'

The next example shows that nulls have no effect on the result of a concatenation:

'suit' || NULL || 'case' = 'suitcase'

A null string (''), which is zero characters in length, is treated like a null.

Usage Notes

In a Boolean expression, you can only compare values that have compatible datatypes. For more information, see "Datatype Conversion".

In conditional control statements, if a Boolean expression yields TRUE, its associated sequence of statements is executed. But, if the expression yields FALSE or NULL, its associated sequence of statements is not executed.

The relational operators can be applied to operands of type BOOLEAN. By definition, TRUE is greater than FALSE. Comparisons involving nulls always yield a null. The value of a Boolean expression can be assigned only to Boolean variables, not to host variables or database columns. Also, datatype conversion to or from type BOOLEAN is not supported.

You can use the addition and subtraction operators to increment or decrement a date value, as the following examples show:

hire_date := '10-MAY-95';
hire_date := hire_date + 1;  -- makes hire_date '11-MAY-95'
hire_date := hire_date - 5;  -- makes hire_date '06-MAY-95'

When PL/SQL evaluates a boolean expression, NOT has the highest precedence, AND has the next-highest precedence, and OR has the lowest precedence. However, you can use parentheses to override the default operator precedence.

Within an expression, operations occur in their predefined order of precedence. From first to last (top to bottom), the default order of operations is

parentheses

exponents

unary operators

multiplication and division

addition, subtraction, and concatenation

PL/SQL evaluates operators of equal precedence in no particular order. When parentheses enclose an expression that is part of a larger expression, PL/SQL evaluates the parenthesized expression first, then uses the result in the larger expression. When parenthesized expressions are nested, PL/SQL evaluates the innermost expression first and the outermost expression last.

Examples

Several examples of expressions follow:

(a + b) > c             -- Boolean expression
NOT finished            -- Boolean expression
TO_CHAR(acct_no)        -- character expression
'Fat ' || 'cats'        -- character expression
'15-NOV-95'             -- date expression
MONTHS_BETWEEN(d1, d2)  -- date expression
pi * r**2               -- numeric expression
emp_cv%ROWCOUNT         -- numeric expression

Related Topics

Assignment Statement, Constants and Variables, EXIT Statement, IF Statement, LOOP Statements