NULL Handling in C# vs. PowerScript/SQL

Details: Written by Michael Kramer; Category: PowerBuilder; Published: 09 March 2020; Last Updated: 09 March 2020; Hits: 1671

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C# handles NULL quite different than PowerScript and SQL.
Same code in PowerScript and C# may have different outcome.

Welcome to a set of examples showing you how C# handles NULL different than PowerScript.
In fact so different that same code can have completely different outcome.

Example 1 : Boolean Data Types

C# by default defines the Boolean data type without NULL.
You can opt-in NULL using the nullable operator (question mark).

	PowerScript	C#	C#
Data type	`Boolean`	`bool`	`bool?`
Possible values	true, false, null	true, false	true, false, null

Example 2 : Conditional Expressions

C# evaluates conditional expressions to its not-NULL Boolean type.
Conditional expressions in C# therefore often have different value than in PowerScript.
Adding null to the Boolean data type has no impact.

PowerScript Syntax	Boolean result	vs.	C# Syntax	bool result	bool? result
`result = (null > 42)`	null		`result = (null > 42)`	false	false
`result = (null <> 42)`	null		`result = (null != 42)`	true	true
`result = (null = null)`	null		`result = (null == null)`	true	true
`result = (null <> null)`	null		`result = (null != null)`	false	false

Example 3 : Equality in IF, DO, and WHILE statements

Check for equality in IF, DO, and WHILE statements has different behavior in C# when comparing to NULL values.

Name1	Name2	PowerScript	C#
		`if (Name1 = Name2) then result = "NORTH" else result = "South" end if`	`if (Name1 == Name2) result = "NORTH"; else result = "South";`
null	null	result = "South"	result = "NORTH"
null	"Mick"	result = "South"	result = "South"

Example 4 : Inequality in IF, DO, and WHILE statements

Similar differences exist when checking for inequality.

Name1	Name2	PowerScript	C#
		`if (Name1 <> Name2) then result = "NORTH" else result = "South" end if`	`if (Name1 != Name2) result = "NORTH"; else result = "South";`
null	null	result = "South"	result = "South"
null	"Mick"	result = "South"	result = "NORTH"

Example 5 : Check for NULL

Syntax for NULL is very different in C# though easy to read and type.

Check	PowerScript	C#
name IS NULL	`if IsNull(name) then ...`	`if (name == null) ...`
name IS NOT NULL	`if not IsNull(name) then ...`	`if (name != null) ...`

Conclusion

"Mind your step!" as you cross between PowerScript + SQL on one side and C# on the other side!

NULL handling is so different in C# that same code sometimes results in completely different outcomes.
Notice in DO and WHILE loops, difference may result in endless loops!

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