Averiguá que "collation" estás usando. Las que terminan en _ci ("case in
sensitive", mayúsculas/minúsculas son indisitintas) son las que necesitás.
By default, MySQL searches are not case sensitive (although there are some character sets that are never case insensitive, such as czech). This means that if you search with col_name LIKE 'a%', you get all column values that start with A or a. If you want to make this search case sensitive, make sure that one of the operands has a case sensitive or binary collation. For example, if you are comparing a column and a string that both have the latin1 character set, you can use the COLLATE operator to cause either operand to have the latin1_general_cs or latin1_bin collation. For example:
col_name COLLATE latin1_general_cs LIKE 'a%'
col_name LIKE 'a%' COLLATE latin1_general_cs
col_name COLLATE latin1_bin LIKE 'a%'
col_name LIKE 'a%' COLLATE latin1_bin
If you want a column always to be treated in case-sensitive fashion, declare it with a case sensitive or binary collation. See Section 13.1.5, “CREATE TABLE Syntax”.