Use the Expression dialog box to formulate mathematical and alphanumeric expressions in several MapInfo Pro dialog boxes. See Specifying an Expression in the Help System.
Expressions are used in the following commands: Select, Update Column, Add Theme and for labeling operations. Highlight a layer in the Layers or Explorer windows to display a LABELS tab on the ribbon where you can create expressions for labels. Alternatively, double-click on a layer to open the Layer Properties dialog box. The Label Display tab provides access to the Expressions dialog box. The expression serves a different purpose in different commands.
For example:
- In the Select command the expression states a condition that a record in a table must meet in order to be included in a query table.
- In Update Column the expression calculates a value that is then entered into a table.
- In Thematic Mapping the expression calculates a value that is then displayed on a map.
- In Label Properties you use expressions containing string functions to fine tune your labels.
The expressions fall into two broad categories:
- Expressions that must evaluate to true or false.
- Expressions that simply calculate some value.
Expressions that must evaluate to true or false always have a comparison operator and may have multiple clauses connected by logical operators. Use these expressions for selecting objects.
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.