当索引过多时，维护开销增大，因此，需要删除不必要的索引。

    格式

    1. DROP INDEX indexname 
    2.    ON tblname;

    示例

    1. DROP INDEX test_index ON test;

    报错

    • 语法错误时报ERROR 1064 (42000): You have an error in your SQL syntax;

    • 输入表名错误时，报ERROR 1146 (42S02): Table 'XXX' doesn't exist

    • 输入表名过长，报ERROR 1059 (42000): Identifier name 'XXX' is too long

    • 输入索引错误，报ERROR 1091 (42000): Can't DROP 'XXX'; check that column/key exists