Update readme.md

Author: ppiyush13

readme.md

@@ -79,7 +79,7 @@ Will output:
 
 SELECT A, B, count(D) AS CNT FROM STUDENTS
 WHERE NAME = 'Piyush' AND ROLL = 13 AND (A = 5 OR A = 10) AND 
-BIRTH BETWEEN '1975-01-01' AND '1999-12-31'
+BIRTH BETWEEN ( '1975-01-01' AND '1999-12-31' )
 GROUP BY A, B, C
 ORDER BY A
 EXTERNAL NAME 'TestFuncs$MyMath.pow'