Char VS VarChar

That is an interesting question posted on regarding the topic of Char or Varchar? - You Decide (by John Koziol). The question asked, Char data type is faster or VarChar?

While waiting for reply from John Koziol, I have a simple test on this as code below. The result is, using Char data type would be slighly faster than VarChar. The differences is about 100 - 200 miliseconds. Most importantly, this test is run on PII 266, 128 RAM, WinXP machine. You may not see any difference in fast machine. Therefore, in my opinion, you decide which data type you want to use.

CLEAR ALL



LOCAL lcUnique



SET TALK OFF



CREATE CURSOR myCursor (Field1 C(20))



FOR I = 1 TO 1000

	lcUnique = SYS(2015)

	INSERT INTO myCursor VALUES ;

         (lcUnique + REPLICATE("A", INT(RAND() * 10)))

NEXT



INDEX ON Field1 TAG Field1



SET VARCHARMAPPING OFF



lnSecond = SECONDS()

FOR I= 1 TO 1000

	SELECT * FROM myCursor WHERE .T. INTO CURSOR TEMP

NEXT



?SET("VARCHARMAPPING") + [ - ] + TRANSFORM(SECONDS() - lnSecond)



SELECT TEMP



lnSecond = SECONDS()

FOR I = 1 TO 100

	LOCATE FOR Field1 = lcUnique

NEXT



?[LOCATE - ] + TRANSFORM(SECONDS() -lnSecond)

Instruction
1. Run the code above
2. Record the elapse time
3. Change setting SET VARMAPPING OFF to SET VARMAPPING ON, and run it again.

Do you get same result as me, CHAR would perform slightly faster than VarChar?
If my memory serve me right, one of UT member explained that, this behavior caused by VFP need extra steps to take care of VARCHAR.

For example, you have a Name field with VARCHAR data type, length 30. If user key in 15 characters, VFP would replace the remaining spaces with CHR(0), and last byte with the actual number of characters stored in this field, which is value 15 in this case.