Literals and Constants in ABAP SQL
The simplest expressions are literals. Just like ABAP itself, ABAP SQL knows two kinds of literals: text literals, specified in simple quotes, and number literals, which can be positive or negative whole numbers. The type of literals in ABAP SQL is the same as in ABAP: Text literals are of type C and number literals are of type I.
In the example, the first element of the field list is a text literal, whereas the second and third element are number literals, one with a positive value and the other with a negative value.
Instead of using literals directly, you are recommended to define constants and use them inside your ABAP SQL statement. This improves readability and gives you access to more types than just C and I. When you use a constant in an ABAP SQL statement, the prefix @ is mandatory.
In the example, the fourth element of the element list is a constant of name C_NUMBER of type I and value 1234.