SQL functions and what they do

SQL is the acronym for Structured Query Language.  A syntax for retrieving and manipulating data from a relational database. SQL has become an industry standard query language in most relational database management systems.

 

The Field Calculator is used to construct SQL expressions to do calculations based on either the Geometry or the current attributes of the selected layer.  By using a combination of Fields, Operators and Functions, an SQL expression can be build to do a specific calculation.  It also allow the user to do general attribute management of the values in each field (e.g. to round a number or split text string in portions)

 

The following section gives an overview of SQL as well as a description of each function included in the MapAble Field Calculator.

 

SQL is a special-purpose programming language designed for managing data held in a relational database management system (RDBMS) or Spatial databases, such as MapAble.  SQL is the standard language for Relation Database System. All relational database management systems like MySQL, MS Access, Oracle, Sybase, Informix, postgres and SQL Server use SQL as standard database language.

 

When you are executing an SQL command for any RDBMS (which includes the MapAble Spatial Database with its spatial relations), the system determines the best way to carry out your request and SQL engine figures out how to interpret the task.

 

 

The following is a classification of the available SQL function in the MapAble Field Calculator and describes for what purpose to use them: (click on the type to be directed to the descriptions)

 

Converting string to numbers and vice versa

 

To manipulate string or alphanumerical fields

 

To calculate area, length, diameter and x,y coordinates

 

To calculate new values based on number fields

 

To create unique values for objects in a layer