ALTERDATABASEdb_nameDEFAULTCHARACTERSETcharacter_name[COLLATE…];

把表默认的字符集和所有字符列（CHAR,VARCHAR,TEXT）改为新的字符集：

ALTERTABLEtbl_nameDEFAULTCHARACTERSETcharacter_name[COLLATE…];

如：ALTERTABLEmyAPP_cont1DEFAULTCHARACTERSETutf8;

修改字段的字符集：

ALTERTABLEtbl_nameCHANGEc_namec_nameCHARACTERSETcharacter_name[COLLATE…];

如：

ALTERTABLElogtestCHANGEtitletitleVARCHAR(100)CHARACTERSETutf8COLLATEutf8_general_ci;

ALTERTABLEmyAPP_cont1CHANGEtitlestitlesVARCHAR(100)CHARACTERSETutf8;

查看数据库编码：

SHOWCREATEDATABASEdb_name;

查看表编码：

SHOWCREATETABLEtbl_name;

查看字段编码：

SHOWFULLCOLUMNSFROMtbl_name;

添加主键或索引

1.添加主键

ALTERTABLE表名ADDPRIMARYKEY(字段名);

altertabletable_aADDPRIMARYKEY(id);

2.删除主键

ALTERTABLE表名DROPPRIMARYKEY;

altertabletable_aDROPPRIMARYKEY;

3.添加唯一索引

ALTERTABLE表名ADDUNIQUE索引名(字段名);

altertabletable_aADDUNIQUEcolumn_a_unique_index(column_a);

4.添加普通索引

ALTERTABLE表名ADDINDEX索引名(字段名);

altertabletable_aADDINDEXcolumn_a_index(column_a);

5.删除索引

ALTERTABLE表名DROPINDEX索引名;

altertabletable_aDROPINDEXcolumn_a_index;