Oracle SQL in 10 Minutes - Asim Abbasi

Chapter 2: SQL Operators

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Figure 4: SQL Operators: Comparison, Arithmetic, Logical & Other.
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Just like we used the greater than (>) operator in the previous examples, there are other SQL operator too. They are mostly used in the WHERE clause to filter certain records or to reduce the number of records in the output. “Reduce the number of records”, what this means? Why we need to reduce the number of records in the output. Imagine a SSA (Social Security Administration) office. The database they are having must be having millions of records in it. You can well realize the drawback, if someone would execute the following statement.

SELECT *
FROM ssa;

Another aspect is, why to look at something you don’t need. If you are looking someone’s information then why to execute the query that will give you all the records rather than execute the following query.

SELECT *
FROM ssa
WHERE ssn = ‘123-455-6677’;

The way we have used the “greater than” operator, on the same lines we can use the “less than” (<), “equal to” (=), “less than equal to” (<=) & “greater than equal to” (>=). ANY/SOME and ALL can be best understood by first looking at their respective real world example.

Example:

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

Compares a value to each value in a list or returned by a query. Must be preceded by =, !=, >, <, <=, >=. Evaluates to FALSE if the query returns no rows.

Example:

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

Compares a value to every value in a list or returned by a query. Must be preceded by =, !=, >, <, <=, >=. Evaluates to TRUE if the query returns no rows.

Chapter 1: SQL Operators

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Oracle SQL in 10 Minutes - Asim Abbasi