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 項12.1.8. 「CREATE TABLE 構文」.

Simple comparison operations (>=, >, =, <, <=, sorting, and grouping) are based on each character's 「sort value.」 Characters with the same sort value (such as ‘E’, ‘e’, and ‘é’) are treated as the same character.