SQL Operators

SQL Operators

1.1 SQL Operators Overview

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. There are two general classes of operators: unary and binary. Oracle Database Lite SQL also supports set operators.

1.1.1 Unary Operators

A unary operator uses only one operand. A unary operator typically appears with its operand in the following format.
operator operand

1.1.2 Binary Operators

A binary operator uses two operands. A binary operator appears with its operands in the following format.
operand1 operator operand2

1.1.3 Set Operators

Set operators combine sets of rows returned by queries, instead of individual data items. All set operators have equal precedence. Oracle Database Lite supports the following set operators.
·         UNION
·         UNION ALL
·         INTERSECT
·         MINUS
The levels of precedence among the Oracle Database Lite SQL operators from high to low are listed in Table 2-1. Operators listed on the same line have the same level of precedence.
Table 2-1 Levels of Precedence of the Oracle Database Lite SQL Operators
Precedence Level
SQL Operator
1
Unary + - arithmetic operators, PRIOR operator
2
* / arithmetic operators
3
Binary + - arithmetic operators, || character operators
4
All comparison operators
5
NOT logical operator
6
AND logical operator
7
OR logical operator

1.1.4 Other Operators

Other operators with special formats accept more than two operands. If an operator receives a null operator, the result is always null. The only operator that does not follow this rule is CONCAT.

1.2 Arithmetic Operators

Arithmetic operators manipulate numeric operands. The '-' operator is also used in date arithmetic. Supported arithmetic operators are listed in Table 2-2.
Table 2-2 Arithmetic Operators
Operator
Description
Example
+ (unary)
Makes operand positive
SELECT +3 FROM DUAL;
- (unary)
Negates operand
SELECT -4 FROM DUAL;
/
Division (numbers and dates)
SELECT SAL / 10 FROM EMP;
*
Multiplication
SELECT SAL * 5 FROM EMP;
+
Addition (numbers and dates)
SELECT SAL + 200 FROM EMP;
-
Subtraction (numbers and dates)
SELECT SAL - 100 FROM EMP;

1.3 Character Operators

Character operators used in expressions to manipulate character strings are listed in Table 2-3.
Table 2-3 Character Operators
Operator
Description
Example
||
Concatenates character strings
SELECT 'The Name of the employee is: ' || ENAME FROM EMP;

 

1.3.1 Concatenating Character Strings

With Oracle Database Lite, you can concatenate character strings with the following results.
·         Concatenating two character strings results in another character string.
·         Oracle Database Lite preserves trailing blanks in character strings by concatenation, regardless of the strings' datatypes.
·         Oracle Database Lite provides the CONCAT character function as an alternative to the vertical bar operator. For example,
·                SELECT CONCAT (CONCAT (ENAME, ' is a '),job) FROM EMP WHERE SAL > 2000;
·                 
This returns the following output.
CONCAT(CONCAT(ENAME
-------------------------
KING       is a PRESIDENT
BLAKE      is a MANAGER
CLARK      is a MANAGER
JONES      is a MANAGER
FORD       is a ANALYST
SCOTT      is a ANALYST
 
6 rows selected.
 
·         Oracle Database Lite treats zero-length character strings as nulls. When you concatenate a zero-length character string with another operand the result is always the other operand. A null value can only result from the concatenation of two null strings.

1.4 Comparison Operators

Comparison operators used in conditions that compare one expression with another are listed in Table 2-4. The result of a comparison can be TRUE, FALSE, or UNKNOWN.
Table 2-4 Comparison Operators
Operator
Description
Example
=
Equality test.
SELECT ENAME "Employee" FROM EMP WHERE SAL = 1500;
!=, ^=, <>
Inequality test.
SELECT ENAME FROM EMP WHERE SAL ^= 5000;
>
Greater than test.
SELECT ENAME "Employee", JOB "Title" FROM EMP WHERE SAL > 3000;
<
Less than test.
SELECT * FROM PRICE WHERE MINPRICE < 30;
>=
Greater than or equal to test.
SELECT * FROM PRICE WHERE MINPRICE >= 20;
<=
Less than or equal to test.
SELECT ENAME FROM EMP WHERE SAL <= 1500;
IN
"Equivalent to any member of" test. Equivalent to "=ANY".
SELECT * FROM EMP WHERE ENAME IN ('SMITH', 'WARD');
ANY/ SOME
Compares a value to each value in a list or returned by a query. Must be preceded by =, !=, >, <, <= or >=. Evaluates to FASLE if the query returns no rows.
SELECT * FROM DEPT WHERE LOC = SOME ('NEW YORK','DALLAS');
NOT IN
Equivalent to "!=ANY". Evaluates to FALSE if any member of the set is NULL.
SELECT * FROM DEPT WHERE LOC NOT IN ('NEW YORK', 'DALLAS');
ALL
Compares a value with every value in a list or returned by a query. Must be preceded by =, !=, >, <, <= or >=. Evaluates to TRUE if the query returns no rows.
SELECT * FROM emp WHERE sal >= ALL (1400, 3000);
[NOT] BETWEEN x and y
[Not] greater than or equal to x and less than or equal to y.
SELECT ENAME, JOB FROM EMP WHERE SAL BETWEEN 3000 AND 5000;
EXISTS
TRUE if a sub-query returns at least one row.
SELECT * FROM EMP WHERE EXISTS (SELECT ENAME FROM EMP WHERE MGR IS NULL);
x [NOT] LIKE y [ESCAPE z]
TRUE if x does [not] match the pattern y. Within y, the character "%" matches any string of zero or more characters except null. The character "_" matches any single character. Any character following ESCAPE is interpreted literally, useful when y contains a percent (%) or underscore (_).
SELECT * FROM EMP WHERE ENAME LIKE '%E%';
IS [NOT] NULL
Tests for nulls. This is the only operator that should be used to test for nulls.
SELECT * FROM EMP WHERE COMM IS NOT NULL AND SAL > 1500;

1.5 Logical Operators

Logical operators which manipulate the results of conditions are listed in Table 2-5.
Table 2-5 Logical Operators
Operator
Description
Example
NOT
Returns TRUE if the following condition is FALSE. Returns FALSE if it is TRUE. If it is UNKNOWN, it remains UNKNOWN.
SELECT * FROM EMP WHERE NOT (job IS NULL)
SELECT * FROM EMP WHERE NOT (sal BETWEEN 1000 AND 2000)
AND
Returns TRUE if both component conditions are TRUE. Returns FALSE if either is FALSE; otherwise returns UNKNOWN.
SELECT * FROM EMP WHERE job='CLERK' AND deptno=10
OR
Returns TRUE if either component condition is TRUE. Returns FALSE if both are FALSE. Otherwise, returns UNKNOWN.
SELECT * FROM emp WHERE job='CLERK' OR deptno=10

1.6 Set Operators

Set operators which combine the results of two queries into a single result are listed in Table 2-6.
Table 2-6 Set Operators
Operator
Description
Example
UNION
Returns all distinct rows selected by either query.
SELECT * FROM
(SELECT ENAME FROM EMP WHERE JOB = 'CLERK'
UNION
SELECT ENAME FROM EMP WHERE JOB = 'ANALYST');
UNION ALL
Returns all rows selected by either query, including all duplicates.
SELECT * FROM
(SELECT SAL FROM EMP WHERE JOB = 'CLERK'
UNION
SELECT SAL FROM EMP WHERE JOB = 'ANALYST');
INTERSECT and INTERSECT ALL
Returns all distinct rows selected by both queries.
SELECT * FROM orders_list1
INTERSECT
SELECT * FROM orders_list2
MINUS
Returns all distinct rows selected by the first query but not the second.
SELECT * FROM (SELECT SAL FROM EMP WHERE JOB = 'PRESIDENT'
MINUS
SELECT SAL FROM EMP WHERE JOB = 'MANAGER');




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