Database Reference
In-Depth Information
The query results appear in Figure 3-7.
79
Customers with credit
limits of $10,000
FIGURE 3-7
Query results
The WHERE clause shown in Figure 3-6 includes a simple condition. A simple condition includes the
field name, a comparison operator, and either another field name or a value, such as CreditLimit
10000 or
¼
CreditLimit
Balance. Figure 3-8 lists the comparison operators that you can use in SQL commands. Notice
that there are two versions of the
>
. You must use the correct one for
your version of SQL. If you use the wrong one, your system will generate an error, in which case, you
“
not equal to
”
operator:
and !
<>
¼
'
ll know
to use the other version.
Comparison Operator
Meaning
=
Equal to
<
Less than
>
Greater than
<=
Less than or equal to
>=
Greater than or equal to
< >
Not equal to (used by most implementations of SQL)
!=
Not equal to (used by some implementations of SQL)
FIGURE 3-8
Comparison operators used in SQL commands
In Example 4, the WHERE clause compared a numeric field (CreditLimit) to a number (10000). When a
query involves a character field, such as CustomerNum or CustomerName, you must enclose the value to
which the field is being compared in single quotation marks, as illustrated in Examples 5 and 6.
EXAMPLE 5
Find the name of customer 148.
The query design appears in Figure 3-9. Because CustomerNum is a character field, the value 148 is
enclosed in single quotation marks.
