3
Operators

An operator manipulates individual data items and returns a result. The data items are called operands or arguments. Operators are represented by special characters or by keywords. For example, the multiplication operator is represented by an asterisk (*) and the operator that tests for nulls is represented by the keywords IS NULL.

This chapter contains these sections:

• Unary and Binary Operators

• Precedence

• Arithmetic Operators

• Concatenation Operator

• Comparison Operators

• Logical Operators: NOT, AND, OR

• Set Operators: UNION [ALL], INTERSECT, MINUS

• Other Built-In Operators

• User-Defined Operators

Unary and Binary Operators

The two general classes of operators are:

unary	A unary operator operates on only one operand. A unary operator typically appears with its operand in this format:
	operator operand
binary	A binary operator operates on two operands. A binary operator appears with its operands in this format:
	operand1 operator operand2

Other operators with special formats accept more than two operands. If an operator is given a null operand, the result is always null. The only operator that does not follow this rule is concatenation (||).

Precedence

Precedence is the order in which Oracle evaluates different operators in the same expression. When evaluating an expression containing multiple operators, Oracle evaluates operators with higher precedence before evaluating those with lower precedence. Oracle evaluates operators with equal precedence from left to right within an expression.

Table 3-1 lists the levels of precedence among SQL operators from high to low. Operators listed on the same line have the same precedence.

Table 3-1 SQL Operator Precedence  

Precedence Example

In the following expression, multiplication has a higher precedence than addition, so Oracle first multiplies 2 by 3 and then adds the result to 1.

1+2*3 

You can use parentheses in an expression to override operator precedence. Oracle evaluates expressions inside parentheses before evaluating those outside.

SQL also supports set operators (UNION, UNION ALL, INTERSECT, and MINUS), which combine sets of rows returned by queries, rather than individual data items. All set operators have equal precedence.

Arithmetic Operators

You can use an arithmetic operator in an expression to negate, add, subtract, multiply, and divide numeric values. The result of the operation is also a numeric value. Some of these operators are also used in date arithmetic. Table 3-2 lists arithmetic operators.

Table 3-2 Arithmetic Operators

SELECT * FROM orders
 WHERE qtysold = -1;
SELECT * FROM emp
  WHERE -sal < 0;

SELECT sal + comm FROM emp
  WHERE SYSDATE - hiredate
  > 365;

UPDATE emp
  SET sal = sal * 1.1;

Do not use two consecutive minus signs (--) in arithmetic expressions to indicate double negation or the subtraction of a negative value. The characters -- are used to begin comments within SQL statements. You should separate consecutive minus signs with a space or a parenthesis.

Concatenation Operator

The concatenation operator manipulates character strings. Table 3-3 describes the concatenation operator.

Table 3-3 Concatenation Operator

SELECT 'Name is ' || ename
   FROM emp;

The result of concatenating two character strings is another character string. If both character strings are of datatype CHAR, the result has datatype CHAR and is limited to 2000 characters. If either string is of datatype VARCHAR2, the result has datatype VARCHAR2 and is limited to 4000 characters. Trailing blanks in character strings are preserved by concatenation, regardless of the strings' datatypes.

On most platforms, the concatenation operator is two solid vertical bars, as shown in Table 3-3. However, some IBM platforms use broken vertical bars for this operator. When moving SQL script files between systems having different character sets, such as between ASCII and EBCDIC, vertical bars might not be translated into the vertical bar required by the target Oracle environment. Oracle provides the CONCAT character function as an alternative to the vertical bar operator for cases when it is difficult or impossible to control translation performed by operating system or network utilities. Use this function in applications that will be moved between environments with differing character sets.

Although Oracle treats zero-length character strings as nulls, concatenating a zero-length character string with another operand always results in the other operand, so null can result only from the concatenation of two null strings. However, this may not continue to be true in future versions of Oracle. To concatenate an expression that might be null, use the NVL function to explicitly convert the expression to a zero-length string.

Example

This example creates a table with both CHAR and VARCHAR2 columns, inserts values both with and without trailing blanks, and then selects these values and concatenates them. Note that for both CHAR and VARCHAR2 columns, the trailing blanks are preserved.

CREATE TABLE tab1 (col1 VARCHAR2(6), col2 CHAR(6),
        col3 VARCHAR2(6), col4 CHAR(6) );

Table created.

INSERT INTO tab1 (col1,  col2,     col3,     col4)
        VALUES   ('abc', 'def   ', 'ghi   ', 'jkl');

1 row created.

SELECT col1||col2||col3||col4 "Concatenation"
        FROM tab1;

Concatenation
------------------------
abcdef   ghi   jkl

Comparison Operators

Comparison operators compare one expression with another. The result of such a comparison can be TRUE, FALSE, or UNKNOWN.

Table 3-4 lists comparison operators.

Table 3-4  Comparison Operators

=

SELECT *
  FROM emp
  WHERE sal = 1500;

!=
^=
<   >
¬=

SELECT *
  FROM emp
  WHERE sal != 1500;

>

<

SELECT * FROM emp
  WHERE sal > 1500;
SELECT * FROM emp
  WHERE sal < 1500;

>=

<= 

SELECT * FROM emp
  WHERE sal >= 1500;
SELECT * FROM emp
  WHERE sal <= 1500;

IN

SELECT * FROM emp
  WHERE job IN
  ('CLERK','ANALYST');
SELECT * FROM emp
  WHERE sal IN
  (SELECT sal FROM emp
   WHERE deptno = 30);

NOT IN 

SELECT * FROM emp
  WHERE sal NOT IN
  (SELECT sal FROM emp
  WHERE deptno = 30);
SELECT * FROM emp
  WHERE job NOT IN
  ('CLERK', 'ANALYST');

ANY
SOME 

SELECT * FROM emp
  WHERE sal = ANY
  (SELECT sal FROM emp
  WHERE deptno = 30);

ALL 

SELECT * FROM emp
  WHERE sal >=
  ALL ( 1400, 3000);

[NOT] 
BETWEEN x 
AND y

SELECT * FROM emp
  WHERE sal
  BETWEEN 2000 AND 3000;

EXISTS 

SELECT ename, deptno 
  FROM dept
  WHERE EXISTS
  (SELECT * FROM emp
    WHERE dept.deptno 
    = emp.deptno);

x [NOT] LIKE 
y 

[ESCAPE 'z'] 

SELECT * FROM tab1
  WHERE col1 LIKE
  'A_C/%E%' ESCAPE '/';

IS [NOT] 
NULL 

SELECT ename, deptno
  FROM emp
  WHERE comm IS NULL;

Additional information on the NOT IN and LIKE operators appears in the sections that follow.

NOT IN Operator

If any item in the list following a NOT IN operation is null, all rows evaluate to UNKNOWN (and no rows are returned). For example, the following statement returns the string 'TRUE' for each row:

SELECT 'TRUE' 
    FROM emp 
    WHERE deptno NOT IN (5,15); 

However, the following statement returns no rows:

SELECT 'TRUE' 
    FROM emp 
    WHERE deptno NOT IN (5,15,null); 

The above example returns no rows because the WHERE clause condition evaluates to:

deptno != 5 AND deptno != 15 AND deptno != null 

Because all conditions that compare a null result in a null, the entire expression results in a null. This behavior can easily be overlooked, especially when the NOT IN operator references a subquery.

LIKE Operator

The LIKE operator is used in character string comparisons with pattern matching. The syntax for a condition using the LIKE operator is shown in this diagram:

char1	Specify a value to be compared with a pattern. This value can have datatype CHAR or VARCHAR2.
NOT	The NOT keyword logically inverts the result of the condition, returning FALSE if the condition evaluates to TRUE and TRUE if it evaluates to FALSE.
char2	Specify the pattern to which char1 is compared. The pattern is a value of datatype CHAR or VARCHAR2 and can contain the special pattern matching characters % and _.
ESCAPE	Specify for esc_char a single character as the escape character. The escape character can be used to cause Oracle to interpret % or _ literally, rather than as a special character. If you wish to search for strings containing an escape character, you must specify this character twice. For example, if the escape character is '/', to search for the string 'client/server', you must specify, 'client//server'.

Whereas the equal (=) operator exactly matches one character value to another, the LIKE operator matches a portion of one character value to another by searching the first value for the pattern specified by the second. Note that blank padding is not used for LIKE comparisons.

With the LIKE operator, you can compare a value to a pattern rather than to a constant. The pattern must appear after the LIKE keyword. For example, you can issue the following query to find the salaries of all employees with names beginning with 'SM':

SELECT sal 
    FROM emp 
    WHERE ename LIKE 'SM%';

The following query uses the = operator, rather than the LIKE operator, to find the salaries of all employees with the name 'SM%':

SELECT sal 
    FROM emp 
    WHERE ename = 'SM%';

The following query finds the salaries of all employees with the name 'SM%'. Oracle interprets 'SM%' as a text literal, rather than as a pattern, because it precedes the LIKE operator:

SELECT sal 
    FROM emp 
    WHERE 'SM%' LIKE ename;

Patterns typically use special characters that Oracle matches with different characters in the value:

• An underscore (_) in the pattern matches exactly one character (as opposed to one byte in a multibyte character set) in the value.

• A percent sign (%) in the pattern can match zero or more characters (as opposed to bytes in a multibyte character set) in the value. Note that the pattern '%' cannot match a null.

Case Sensitivity and Pattern Matching

Case is significant in all conditions comparing character expressions including the LIKE and equality (=) operators. You can use the UPPER function to perform a case-insensitive match, as in this condition:

UPPER(ename) LIKE 'SM%' 

Pattern Matching on Indexed Columns

When LIKE is used to search an indexed column for a pattern, Oracle can use the index to improve the statement's performance if the leading character in the pattern is not "%" or "_". In this case, Oracle can scan the index by this leading character. If the first character in the pattern is "%" or "_", the index cannot improve the query's performance because Oracle cannot scan the index.

LIKE Operator Examples

This condition is true for all ename values beginning with "MA":

ename LIKE 'MA%' 

All of these ename values make the condition TRUE:

MARTIN, MA, MARK, MARY 

Case is significant, so ename values beginning with "Ma," "ma," and "mA" make the condition FALSE.

Consider this condition:

ename LIKE 'SMITH_' 

This condition is true for these ename values:

SMITHE, SMITHY, SMITHS 

This condition is false for 'SMITH', since the special character "_" must match exactly one character of the ename value.

To search for employees with the pattern 'A_B' in their name:

SELECT ename 
    FROM emp 
    WHERE ename LIKE '%A\_B%' ESCAPE '\';

The ESCAPE option identifies the backslash (\) as the escape character. In the pattern, the escape character precedes the underscore (_). This causes Oracle to interpret the underscore literally, rather than as a special pattern matching character.

ESCAPE Option Example

You can include the actual characters "%" or "_" in the pattern by using the ESCAPE option. The ESCAPE option identifies the escape character. If the escape character appears in the pattern before the character "%" or "_" then Oracle interprets this character literally in the pattern, rather than as a special pattern matching character.

Patterns Without %

If a pattern does not contain the "%" character, the condition can be TRUE only if both operands have the same length.

Example:

Consider the definition of this table and the values inserted into it:

CREATE TABLE freds (f CHAR(6), v VARCHAR2(6));
INSERT INTO freds VALUES ('FRED', 'FRED');

Because Oracle blank-pads CHAR values, the value of f is blank-padded to 6 bytes. v is not blank-padded and has length 4.

Logical Operators: NOT, AND, OR

A logical operator combines the results of two component conditions to produce a single result based on them or to invert the result of a single condition. Table 3-5 lists logical operators.

Table 3-5 Logical Operators  

NOT 

SELECT *
  FROM emp
  WHERE NOT (job IS NULL);
SELECT *
  FROM emp
  WHERE NOT 
  (sal BETWEEN 1000 AND 2000);

AND 

SELECT *
  FROM emp
  WHERE job = 'CLERK'
  AND deptno = 10;

OR 

SELECT *
  FROM emp
  WHERE job = 'CLERK'
  OR deptno = 10;

For example, in the WHERE clause of the following SELECT statement, the AND logical operator is used to ensure that only those hired before 1984 and earning more than $1000 a month are returned:

SELECT * 
    FROM emp 
    WHERE hiredate < TO_DATE('01-JAN-1984', 'DD-MON-YYYY') 
        AND sal > 1000;

NOT Operator

Table 3-6 shows the result of applying the NOT operator to a condition.

Table 3-6 NOT Truth Table

AND Operator

Table 3-7 shows the results of combining two expressions with AND.

Table 3-7 AND Truth Table

OR Operator

Table 3-8 shows the results of combining two expressions with OR.

Table 3-8 OR Truth Table

Set Operators: UNION [ALL], INTERSECT, MINUS

Set operators combine the results of two component queries into a single result. Queries containing set operators are called compound queries. Table 3-9 lists SQL set operators.

Table 3-9 Set Operators

All set operators have equal precedence. If a SQL statement contains multiple set operators, Oracle evaluates them from the left to right if no parentheses explicitly specify another order.

The corresponding expressions in the select lists of the component queries of a compound query must match in number and datatype. If component queries select character data, the datatype of the return values are determined as follows:

• If both queries select values of datatype CHAR, the returned values have datatype CHAR.

• If either or both of the queries select values of datatype VARCHAR2, the returned values have datatype VARCHAR2.

Set Operator Examples

Consider these two queries and their results:

SELECT part
    FROM orders_list1;

PART 
---------- 
SPARKPLUG 
FUEL PUMP 
FUEL PUMP 
TAILPIPE 

SELECT part 
    FROM orders_list2;

PART 
---------- 
CRANKSHAFT 
TAILPIPE 
TAILPIPE 

The following examples combine the two query results with each of the set operators.

UNION Example

The following statement combines the results with the UNION operator, which eliminates duplicate selected rows. This statement shows that you must match datatype (using the TO_DATE and TO_NUMBER functions) when columns do not exist in one or the other table:

SELECT part, partnum, to_date(null) date_in
    FROM orders_list1
UNION
SELECT part, to_number(null), date_in
    FROM orders_list2;

PART       PARTNUM DATE_IN
---------- ------- -------- 
SPARKPLUG  3323165 
SPARKPLUG          10/24/98
FUEL PUMP  3323162
FUEL PUMP          12/24/99
TAILPIPE   1332999
TAILPIPE           01/01/01
CRANKSHAFT 9394991
CRANKSHAFT         09/12/02

SELECT part 
    FROM orders_list1 
UNION 
SELECT part 
    FROM orders_list2;

PART 
---------- 
SPARKPLUG 
FUEL PUMP 
TAILPIPE 
CRANKSHAFT 

UNION ALL Example

The following statement combines the results with the UNION ALL operator, which does not eliminate duplicate selected rows:

SELECT part 
    FROM orders_list1 
UNION ALL 
SELECT part 
    FROM orders_list2;

PART 
---------- 
SPARKPLUG 
FUEL PUMP 
FUEL PUMP 
TAILPIPE 
CRANKSHAFT 
TAILPIPE 
TAILPIPE 

Note that the UNION operator returns only distinct rows that appear in either result, while the UNION ALL operator returns all rows. A part value that appears multiple times in either or both queries (such as 'FUEL PUMP') is returned only once by the UNION operator, but multiple times by the UNION ALL operator.

INTERSECT Example

The following statement combines the results with the INTERSECT operator, which returns only those rows returned by both queries:

SELECT part 
    FROM orders_list1 
INTERSECT 
SELECT part 
    FROM orders_list2;

PART 
---------- 
TAILPIPE 

MINUS Example

The following statement combines results with the MINUS operator, which returns only rows returned by the first query but not by the second:

SELECT part 
    FROM orders_list1 
MINUS 
SELECT part 
    FROM orders_list2;

PART 
---------- 
SPARKPLUG 
FUEL PUMP 

Other Built-In Operators

Table 3-10 lists other SQL operators.

Table 3-10 Other SQL Operators

SELECT ename, dname
  FROM emp, dept
  WHERE dept.deptno =
     emp.deptno(+);

SELECT empno, ename, 
mgr
  FROM emp
  CONNECT BY
     PRIOR empno = 
mgr;

User-Defined Operators

Like built-in operators, user-defined operators take a set of operands as input and return a result. However, you create them with the CREATE OPERATOR statement, and they are identified by names (e.g., MERGE). They reside in the same namespace as tables, views, types, and stand-alone functions.

Once you have defined a new operator, you can use it in SQL statements like any other built-in operator. For example, you can use user-defined operators in the select list of a SELECT statement, the condition of a WHERE clause, or in ORDER BY clauses and GROUP BY clauses. However, you must have EXECUTE privilege on the operator to do so, because it is a user-defined object.

For example, if you define an operator CONTAINS, which takes as input a text document and a keyword and returns 1 if the document contains the specified keyword, you can then write the following SQL query:

SELECT * FROM emp WHERE contains (resume, 'Oracle and UNIX') = 1;