MySQL的一些簡單操作
MySQL新增列的方法:
(1) 新增單列:ALTER TABLE table_name ADD [column] column_name column_definition [FIRST|AFTER] ; 不使用小括號,單列可以設定新增的位置
(2) 新增多列:ALTER TABLE table_name ADD [column] (column_name column_definition,...); 要使用小括號,多列不可以設定新增的位置。
MySQL刪除列的方法:
ALTER TABLE table_name DROP [column] column_name;刪除多列,列之間用逗號分開。刪除的同時要增加列也是可以的,要用逗號分開。
修改列定義:
alter table table_name modify column_name column_definition [first|after column_name];
修改列名稱及列定義:
alter table table_name change old_column_name new_column_name column_definition [first|after column_name];
修改表名稱:
alter table table_name rename [to|as] new_table_name;
MySQL新增約束的方法:
(1) 新增主鍵約束:ALTER TABLE table_name ADD PRIMARY KEY(column_name);
(2) 新增外來鍵約束:ALTER TABLE table_name ADD FOREIGN KEY(column_name,...) REFERENCES
table_name(column_name);
(3) 新增唯一約束:ALTER TABLE table_name ADD UNIQUE KEY(column_name,...);
(4)新增預設約束:
ALTER TABLE table_name ALTER column_name SET DEFAULT literal;
MySQL刪除約束的方法:
(1) 刪除主鍵約束:ALTER TABLE table_name DROP PRIMARY KEY;
(2) 刪除唯一約束:ALTER TABLE table_name DROP {INDEX|KEY} index_name;
(2) 刪除外來鍵約束: ALTER TABLE table_name DROP FOREIGN KEY fk_name;
條件查詢:
簡單條件where子句:
select column_name,... from table_name where where_condition;
分組查詢group by:
select {column_name [...]} from table_name where where_condition group by {column_name|position}[[ASC|DESC],...];
設定分組條件HAVING:
注:使用HAVING時,HAVING後面可以跟聚合函式或欄位,如果跟的是欄位,則欄位必須出現在當前的select語句當中。
select {column_name [...]} from table_name where where_condition group by {column_name|position} [[ASC|DESC],...] HAVING where_condition;
對查詢結果進行排序order by:
select {column_name [...]} from table_name [where where_condition group by {column_name|position} [[ASC|DESC],...] HAVING where_condition] order by {column_name|expr|position..} [ASC|DESC...];
限制查詢結果返回的數量limit:
select column_name from table_name [where where_condition] limit {[off_set],row_count|row_count OFFSET offset};