Why does SQL Join find two dissimilar length strings equal?

I have created a query that uses a left join. For reasons I don't understand it will join two dissimilar length strings as if they are equal. An example would be:

Left column = "351-561"
Right Column = "351-561-35C"
Result = Joined as equal.

My workaround has been to right pad the strings to the same len开发者_开发知识库gth. I don't understand though why those two strings would be treated as equal.

Is there some mechanism in the syntax that would change that behavior?

D.

---

It looks like you may well need to use the == operator in Visual Fox Pro

---

In Visual FoxPro, the = operator means equal. The == operator means "exactly equal". In other words, the == operator compares the size and value of each expression. For example:

* Returns .T. because the first 3 characters on the left match the right.
? "123" = "12345"

* Returns .F. because the expression sizes are not equal.
? "123" == "12345"

That being said, the only reason I can think a JOIN would fail is because the columns you are joining on are not the same size. For example, this query only returns the 555-1234 record because a CHAR column is automatically padded right with spaces.

CREATE CURSOR "MyLeft" (LeftPK I, LeftCode C(20))
INSERT INTO "MyLeft" VALUES(1, "351-561")
INSERT INTO "MyLeft" VALUES(2, "555-1234")

CREATE CURSOR "MyRight" (RightPK I, RightCode C(20))
INSERT INTO "MyRight" VALUES(1, "351-561-35C")
INSERT INTO "MyRight" VALUES(2, "555-1234")

SELECT MyLeft.*, MyRight.* FROM "MyLeft" JOIN "MyRight" ON LeftCode = RightCode

Whereas this query returns both records because the column type is VARCHAR.

CREATE CURSOR "MyLeft" (LeftPK I, LeftCode V(20))
INSERT INTO "MyLeft" VALUES(1, "351-561")
INSERT INTO "MyLeft" VALUES(2, "555-1234")

CREATE CURSOR "MyRight" (RightPK I, RightCode V(20))
INSERT INTO "MyRight" VALUES(1, "351-561-35C")
INSERT INTO "MyRight" VALUES(2, "555-1234")

SELECT MyLeft.*, MyRight.* FROM "MyLeft" JOIN "MyRight" ON LeftCode = RightCode