Can not search concrete value

[yoyosbg]

It will return the Entries by using:
ldapsearch -x -H ldap://localhost:1389 -b "ou=People,dc=example,dc=org" -D "cn=admin,dc=example,dc=org" -w "admin" "(uid=*)" cn sn

but No entries by using:
ldapsearch -x -H ldap://localhost:1389 -b "ou=People,dc=example,dc=org" -D "cn=admin,dc=example,dc=org" -w "admin" "(uid=admin1)" cn sn

(only difference is uid equals: * or admin1)

The admin1 is exists in the entries by using first query!

[yoyosbg]

it seems the search filter string can not use concrete value while (objectClass=*) is also return entries