mysql 删除约束 的SQL语句!

Question

mysql 删除约束 的SQL语句!

Answer 1

用alter table语句：完整用法：ALTER [IGNORE] TABLE tbl_namealter_specification [, alter_specification] ...alter_specification:table_option ...| ADD [COLUMN] column_definition [FIRST | AFTER col_name ]| ADD [COLUMN] (column_definition,...)| ADD {INDEX|KEY} [index_name] [index_type] (index_col_name,...)| ADD [CONSTRAINT [symbol]]PRIMARY KEY [index_type] (index_col_name,...)| ADD [CONSTRAINT [symbol]]UNIQUE [INDEX|KEY] [index_name] [index_type] (index_col_name,...)| ADD [FULLTEXT|SPATIAL] [INDEX|KEY] [index_name] (index_col_name,...)| ADD [CONSTRAINT [symbol]]FOREIGN KEY [index_name] (index_col_name,...)[reference_definition]| ALTER [COLUMN] col_name {SET DEFAULT literal | DROP DEFAULT}| CHANGE [COLUMN] old_col_name column_definition[FIRST|AFTER col_name]| MODIFY [COLUMN] column_definition [FIRST | AFTER col_name]| DROP [COLUMN] col_name| DROP PRIMARY KEY| DROP {INDEX|KEY} index_name| DROP FOREIGN KEY fk_symbol| DISABLE KEYS| ENABLE KEYS| RENAME [TO] new_tbl_name| ORDER BY col_name [, col_name] ...| CONVERT TO CHARACTER SET charset_name [COLLATE collation_name]| [DEFAULT] CHARACTER SET charset_name [COLLATE collation_name]| DISCARD TABLESPACE| IMPORT TABLESPACEindex_col_name:col_name [(length)] [ASC | DESC]index_type:USING {BTREE | HASH}删除 主键 和外键约束:ALTER TABLE mytablenameDROP PRIMARY KEYDROP FOREIGN KEY fk_symbol;还有就是怎么样查询 约束;你可以通过查看该表的 创建语句来 查看 约束：SHOW CREATE TABLE mytablename;得到ddl语句；