Command Comparison Operators

Comparison Operators

4th Dimension 2004, Command Alphabetical List

version 6.5 (Modified)

The tables in this section show the comparison operators as they apply to string, numeric, date, time, and pointer expressions. An expression that uses a comparison operator returns a Boolean value, either TRUE or FALSE.

String Comparisons

Operation Syntax Returns Expression Value

Equality String = String Boolean "abc" = "abc" True

"abc" = "abd" False

Inequality String # String Boolean "abc" # "abd" True

"abc" # "abc" False

Greater than String > String Boolean "abd" > "abc" True

"abc" > "abc" False

Less than String < String Boolean "abc" < "abd" True

"abc" < "abc" False

Greater than or equal to String >= String Boolean "abd" >= "abc" True

"abc" >= "abd" False

Less than or equal to String <= String Boolean "abc" <= "abd" True

"abd" <= "abc" False

Numeric Comparisons

Operation Syntax Returns Expression Value

Equality Number = Number Boolean 10 = 10 True

10 = 11 False

Inequality Number # Number Boolean 10 #11 True

10 # 10 False

Greater than Number > Number Boolean 11 > 10 True

10 > 11 False

Less than Number < Number Boolean 10 < 11 True

11 < 10 False

Greater than or equal to Number >= Number Boolean 11 >= 10 True

10 >= 11 False

Less than or equal to Number <= Number Boolean 10 <= 11 True

11 <= 10 False

Date Comparisons

Operation Syntax Returns Expression Value

Equality Date = Date Boolean !1/1/97! =!1/1/97! True

!1/20/97! =!1/1/97! False

Inequality Date # Date Boolean !1/20/97! # !1/1/97! True

!1/1/97! # !1/1/97! False

Greater than Date > Date Boolean !1/20/97! > !1/1/97! True

!1/1/97! > !1/1/97! False

Less than Date < Date Boolean !1/1/97! < !1/20/97! True

!1/1/97! < !1/1/97! False

Greater than or equal to Date >= Date Boolean !1/20/97! >=!1/1/97! True

!1/1/97!>=!1/20/97! False

Less than or equal to Date <= Date Boolean !1/1/97!<=!1/20/97! True

!1/20/97!<=!1/1/97! False

Time Comparisons

Operation Syntax Returns Expression Value

Equality Time = Time Boolean ?01:02:03? = ?01:02:03? True

?01:02:03? = ?01:02:04? False

Inequality Time # Time Boolean ?01:02:03? # ?01:02:04? True

?01:02:03? # ?01:02:03? False

Greater than Time > Time Boolean ?01:02:04? > ?01:02:03? True

?01:02:03? > ?01:02:03? False

Less than Time < Time Boolean ?01:02:03? < ?01:02:04? True

?01:02:03? < ?01:02:03? False

Greater than or equal to Time >= Time Boolean ?01:02:03? >=?01:02:03? True

?01:02:03? >=?01:02:04? False

Less than or equal to Time <= Time Boolean ?01:02:03? <=?01:02:03? True

?01:02:04? <=?01:02:03? False

Pointer comparisons

With:

      ` vPtrA and vPtrB point to the same object
   vPtrA:=->anObject
   vPtrB:=->anObject
      ` vPtrC points to another object
   vPtrC:=->anotherObject

Operation Syntax Returns Expression Value

Equality Pointer = Pointer Boolean vPtrA = vPtrB True

vPtrA = vPtrC False

Inequality Pointer # Pointer Boolean vPtrA # vPtrC True

vPtrA # vPtrB False

More about string comparisons

• Strings are compared on a character-by-character basis.

• When strings are compared, the case of the characters is ignored; thus, "a"="A" returns TRUE. To test if the case of two characters is different, compare their ASCII codes. For example, the following expression returns FALSE:

   Ascii ("A") = Ascii ("a") ` because 65 is not equal to 97

• When strings are compared, diacritical characters are compared using the system character comparison table of your computer. For example, the following expressions return TRUE:

   "n" = "ñ"
   "n" = "Ñ"
   "A"="å"
      ` and so on

• The wildcard character (@) can be used in any string comparison to match any number of characters. For example, the following expression is TRUE:

   "abcdefghij" = "abc@"

The wildcard character must be used within the second operand (the string on the right side) in order to match any number of characters. The following expression is FALSE, because the @ is considered only as a one character in the first operand:

   "abc@" = "abcdefghij"

The wildcard means "one or more characters or nothing". The following expressions are TRUE:

   "abcdefghij" = "abcdefghij@"
   "abcdefghij" = "@abcdefghij"
   "abcdefghij" = "abcd@efghij"
   "abcdefghij" = "@abcdefghij@"
   "abcdefghij" = "@abcde@fghij@"

On the other hand, whatever the case, a string comparison with two consecutive wildcards will always return FALSE. The following expression is FALSE:

   "abcdefghij" = "abc@@fg"

Tip

If you want to execute comparisons or queries using @ as a character (and not as a wildcard), you have two options:

• Use the Ascii (At sign) instruction.

Imagine, for example, that you want to know if a string ends with the @ character.

- the following expression (if $vsValue is not empty) is always TRUE:

   ($vsValue[[Length($vsValue)]]="@")

- the following expression will be evaluated correctly:

   (Ascii ($vsValue[[Length($vsValue)]])#64)

• Use the "Consider @ as a character for Query and Order By" option which can be accessed using the Preferences dialog box.

This option lets you define how the @ character is interpreted when it is included in a character string. As such, it can influence how comparison operators are used in Query or Order By. For more information, refer to the 4D Design Reference manual.

Operation	Syntax	Returns	Expression	Value
Equality	String = String	Boolean	"abc" = "abc"	True
			"abc" = "abd"	False
Inequality	String # String	Boolean	"abc" # "abd"	True
			"abc" # "abc"	False
Greater than	String > String	Boolean	"abd" > "abc"	True
			"abc" > "abc"	False
Less than	String < String	Boolean	"abc" < "abd"	True
			"abc" < "abc"	False
Greater than or equal to	String >= String	Boolean	"abd" >= "abc"	True
			"abc" >= "abd"	False
Less than or equal to	String <= String	Boolean	"abc" <= "abd"	True
			"abd" <= "abc"	False