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Executing the above statement will produce the output shown in Table 4.22.
Dept_Name Location
Administration Delhi
Home Goods Mumbai
Textile Mumbai
Table 4.22 Departments located in Mumbai or Delhi
4.4.14 IS Operator
Recall from the previous chapter that when the value of an attribute is not known, we use either the default value
(if specified) or the NULL value. We can check whether a value is NULL using IS NULL or IS NOT NULL.
Using the following syntax:
SELECT attribute1, attribute2, ...
FROM table_name
WHERE attributeJ IS [NOT] NULL;
The operator IS NULL returns TRUE if the specified attribute (attributeJ in the above description) has
a NULL value and FALSE otherwise. The operator IS NOT NULL returns TRUE if the specified attribute
(attributeJ in the above description) has a non-NULL value and FALSE otherwise.
For example, to display the department name and the manager ID (from Table 4.23) for the departments having a
manager(means having a value in the attribute Mgr_Id).
SELECT Dept_Name, Mgr_Id
FROM DEPARTMENT
WHERE Mgr_Id IS NOT NULL;
Executing the above statement will produce the output shown in Table 4.23.
Dept_Name Mgr_Id
Administration 10005
Home Goods 10003
Automobile 10007
Textile 10004
Table 4.23 Dept_Name, Mgr_Id for the departments with a manager
4.4.15 LIKE Operator
The SQL LIKE operator uses wildcard operators % and _ to define a pattern. The per cent (%) operator denotes
zero, one, or more occurrences of arbitrary characters. The underscore (_) operator represents exactly one occurrence
of an arbitrary character. If required, we may use a combination of % and _ operators. The syntax for the LIKE
operator is given below:
SELECT attribute1, attribute2, ...
FROM table_name
WHERE attributeJ LIKE 'pattern';
156 Touchpad Informatics Practices-XII

