Pitney Bowes MapInfo Professional - Manual (Page 438)

Expressions that simply calculate some value never have a comparison operator and generally do not
have multiple clauses. Use these expressions to calculate values for Thematic Mapping, Update Column,
and Label With Column in Layer Settings.
Constructing Simple Expressions
You formulate expressions using column (field) names and constants (for example, specific data values),
on the one hand, and functions and operators, on the other. Think of the column names and constants
as nouns, and functions and operators as verbs, prepositions and conjunctions. You always need at
least one column name or a constant in an expression. How many operators and functions you need
depends on what you want to do with your expression.
The simplest possible expression consists of a column name, for example:
1. POP_1990
2. STATE
You could use such an expression in Thematic Mapping to indicate what data is to be represented on
the map. In Update Column such an expression would tell MapInfo Professional what data to use in
updating a column in the target table.
Here are some slightly more complex expressions:
1. POP_1990 > 17893
2. POP_1990 <= POP_1980
3. COUNTY <> "Orange"
4. POP_1980 * 1.2
5. POP_1990 / TOTAL_AREA
6. round(POP_1990/TOTAL_AREA,.1)
The first three examples use comparison operators. The first tests to see whether the 1990 population
is greater than (>) some constant (17893). The second tests to see whether the value of one column,
POP_1990, is less than or equal to (<=) the value of another column, POP_1980. The third tests to see
whether or not the county is Orange. When the county does not equal (<>) "Orange" the record is
selected. You could use any of these expressions in Select or in the Where Condition clause of SQL
Select. These commands allow you to select a subset of the records in a table. The expression defines
the characteristics of the subset.
Examples 6 and 7 use arithmetic operators. Example 6 multiplies (*) the value of POP_1980 by a constant
(1.2) while example 7 divides one column, POP_1990, by the value of another column, AREA.
Example 8 uses the round function to round the value of the expression "POP_1990/TOTAL_AREA" to
the nearest tenth (.1).
Expressions 6, 7 and 8 do not have comparison operators and therefore they would not be suitable for
use in Select or in the Where Condition clause of SQL Select. However, you could use them alone in
Thematic Mapping, Update Column, or Select columns in SQL Select.
Setting Filter Criteria for Expressions
A filter criterion is a logical expression that usually compares a column value against some other value.
For example, the following filter criterion uses the greater-than operator (>) to test whether the
Order_Amount column has a value greater than one hundred:
Where Condition: Order_Amount > 100
If a query includes the preceding Where Condition clause, MapInfo Professional selects only the rows
that have an Order_Amount value greater than one hundred.
The Where Condition field can contain two or more logical expressions if the expressions are separated
by the word And or by the word Or. If the expressions are joined by the word And, MapInfo Professional
only selects the rows that satisfy both criteria. If the expressions are joined by the word Or, MapInfo
Professional selects any row that satisfies either criterion.
MapInfo Professional 12.5 438
Creating Expressions