Basic elements of SQL : Nulls : Nullability

Nullability

Nullability of the resultant column obtained from the CONCAT () function, concat operators (such as ‘+’ or ‘||’), or any other operators (such as ‘+’, ‘-‘, ‘*’, or ‘/’) is calculated based on the nullability of the columns that are being concatenated.

The following truth tables explain the nullability behavior of char and non-char data types.

Char data types

Table 3: Nullability Behavior of char Data Types with CONCAT operators (+ or ||) or Scalar String Functions
Column 1	Column 2	Resultant column (Column 1 (+ or \|\|) Column 2) OR Scalar string function (Column 1, Column 2)
NULLABLE	NULLABLE	NULLABLE
NULLABLE	NON-NULLABLE	NON-NULLABLE
NON-NULLABLE	NULLABLE	NON-NULLABLE
NON-NULLABLE	NON-NULLABLE	NON-NULLABLE

Note: Operators (such as ‘-‘, ‘*’, ‘/’, and so on) are not supported in char data types.

Non-Char data types

Table 4: Nullability behavior of non-char Data Types with All the Other Operators
Column 1	Column 2	Column1 (‘+’, ’ –‘, ’*’, and ‘/’) Column2
NULLABLE	NULLABLE	NULLABLE
NULLABLE	NON-NULLABLE	NULLABLE
NON-NULLABLE	NULLABLE	NULLABLE
NON-NULLABLE	NON-NULLABLE	NON-NULLABLE