2.1 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 Lite SQL also supports set operators.
2.1.1 Unary Operators
A unary operator uses only one operand. A unary operator typically appears with its operand in the following format:
2.1.2 Binary Operators
A binary operator uses two operands. A binary operator appears with its operands in the following format:
operand1 operator operand2
2.1.3 Set Operators
Set operators combine sets of rows returned by queries, instead of individual data items. All set operators have equal precedence. Oracle Lite supports the following set operators:
- UNION ALL
The following lists the levels of precedence among the Oracle Lite SQL operators from high to low. Operators listed on the same line have the same level of precedence:
|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|
2.1.4 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.
2.2 Arithmetic Operators
Arithmetic operators manipulate numeric operands. The – operator is also used in date arithmetic.
Table 2-2 Arithmetic Operators
|+ (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;|
2.3 Character Operators
Character operators are used in expressions to manipulate character strings.
Table 2-3 Character Operators
|||||Concatenates character strings||SELECT ‘The Name of the employee is: ‘ || ENAME FROM EMP;|
2.3.1 Concatenating Character Strings
With Oracle Lite, you can concatenate character strings with the following results:
- Concatenating two character strings results in another character string.
- Oracle Lite preserves trailing blanks in character strings by concatenation, regardless of the strings’ datatypes.
- Oracle 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; ·
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 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.
2.4 Comparison Operators
Comparison operators are used in conditions that compare one expression with another. The result of a comparison can be TRUE, FALSE, or UNKNOWN.
Table 2-4 Comparison Operators
|=||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 FALSE 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] BETWEENx 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[ESCAPEz]||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 interpretted litteraly, 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;|
2.5 Logical Operators
Logical operators manipulate the results of conditions.
Table 2-5 Logical Operators
|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|
2.6 Set Operators
Set operators combine the results of two queries into a single result.
Table 2-6 Set Operators
|UNION||Returns all distinct rows selected by either query.||SELECT * FROM
(SELECT ENAME FROM EMP WHERE JOB = ‘CLERK’
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’
SELECT SAL FROM EMP WHERE JOB = ‘ANALYST’);
|INTERSECT and INTERSECT ALL||Returns all distinct rows selected by both queries.||SELECT * FROM orders_list1
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’
SELECT SAL FROM EMP WHERE JOB = ‘MANAGER’);
2.7 Other Operators
The following lists other operators:
Table 2-7 Other Operators
|(+)||Indicates that the preceding column is the outer join column in a join.||SELECT ENAME, DNAME FROM EMP, DEPT WHERE DEPT.DEPTNO = EMP.DEPTNO (+);|
|PRIOR||Evaluates the following expression for the parent row of the current row in a hierarchical, or tree-structured query. In such a query, you must use this operator in the CONNECT BY clause to define the relationship between the parent and child rows.||SELECT EMPNO, ENAME, MGR FROM EMP CONNECT BY PRIOR EMPNO = MGR;|