Sunday, 15 May 2011

SQL Comparison Keywords

SQL Comparison Keywords

There are other comparison keywords available in sql which are used to enhance the search capabilities of a sql query. They are "IN", "BETWEEN...AND", "IS NULL", "LIKE".

Comparision Operators - Description

LIKE - column value is similar to specified character(s).
IN - column value is equal to any one of a specified set of values.
BETWEEN...AND - column value is between two values, including the end values specified in the range.

IS NULL column value does not exist.

SQL LIKE Operator

The LIKE operator is used to list all rows in a table whose column values match a specified pattern. It is useful when you want to search rows to match a specific pattern, or when you do not know the entire value. For this purpose we use a wildcard character '%'.

For example: To select all the students whose name begins with 'S'

SELECT first_name, last_name
FROM student_details
WHERE first_name LIKE 'S%';

SQL BETWEEN ... AND Operator

The operator BETWEEN and AND, are used to compare data for a range of values.

For Example: to find the names of the students between age 10 to 15 years, the query would be like,

SELECT first_name, last_name, age
FROM student_details
WHERE age BETWEEN 10 AND 15;

SQL IN Operator:

The IN operator is used when you want to compare a column with more than one value. It is similar to an OR condition.

For example: If you want to find the names of students who are studying either Maths or Science, the query would be like,

SELECT first_name, last_name, subject
FROM student_details
WHERE subject IN ('Maths', 'Science');

SQL IS NULL Operator

A column value is NULL if it does not exist. The IS NULL operator is used to display all the rows for columns that do not have a value.

For Example: If you want to find the names of students who do not participate in any games, the query would be as given below

SELECT first_name, last_name
FROM student_details
WHERE games IS NULL

There would be no output as we have every student participate in a game in the table student_details, else the names of the students who do not participate in any games would be displayed.

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