以下是创建表的SQL语句: CREATETABLEusers(idINTAUTO_INCREMENTPRIMARYKEY,usernameVARCHAR(100)NOTNULL,emailVARCHAR(100)NOTNULL); 1. 2. 3. 4. 5. 在上述代码中,我们创建了名为users的表。该表包含三个字段: id:类型为INT,并设置为AUTO_INCREMENT,代表该字段会自动增加,且作为主键。 username:一个用于存储...
#约束CONSTRAINTysPRIMARYKEY(id),#主键CONSTRAINTuqUNIQUE(seat),#唯一键CONSTRAINTckCHECK(sex='男'ORsex='女'),#检查CONSTRAINTfkFOREIGNKEY(majorid)REFERENCESmajor(id)#外键,references指向主键2.添加默认约束ALTERTABLEstuinfo MODIFYCOLUMNageINTDEFAULT18;3.添加主键 #列级约束ALTERTABLEstuinfo MODIFYCOLUMNidINT...
复制 CREATETABLErental(rental_idINTNOTNULLAUTO_INCREMENT,rental_dateDATETIMENOTNULL,inventory_idMEDIUMINTUNSIGNEDNOTNULL,customer_idSMALLINTUNSIGNEDNOTNULL,return_dateDATETIMEDEFAULTNULL,staff_idTINYINTUNSIGNEDNOTNULL,last_updateTIMESTAMPNOTNULLDEFAULTCURRENT_TIMESTAMPONUPDATECURRENT_TIMESTAMP,PRIMARYKEY(rental_id...
如果没有,可以通过如下方式定义: ALTERTABLE`parent`ADDPRIMARYKEY(`id`); 1. 3. 保存设计 在MySQL Workbench 中,确保所有更改已保存后,再尝试设置外键。可以通过点击顶部菜单中的“File” -> “Save”来保存当前设计。 4. 设置外键示例 假设我们已经解决了上述所有问题,接下来可以使用以下代码设置外键: ALTERTAB...
mysql create table primary key auto_increment mysql> create table ss(id intunsignednot nullprimary key auto_increment, user_namevarchar(15)not null); Query OK, 0 rows affected (0.00 sec) mysql> mysql>insert into ss(id,user_name) values(1, 'jojo');...
Primary Keys in All Tables: Ensuring that every table has a primary key is critical. Lack of primary keys can significantly increase replication lag, affecting the downtime. Low Workload During Maintenance Times: Maintenance periods should coincide with times of low workload on the server to ...
ALTER TABLE table ADD [COLUMN] column_name_1 column_1_definition [FIRST|AFTER existing_column], ADD [COLUMN] column_name_2 column_2_definition [FIRST|AFTER existing_column], ...; 在某些情况下,您希望在添加列之前检查表中是否已存在列。但是,没有ADD COLUMN IF NOT EXISTS可用的声明。幸运的是,...
初始化这个index_entry_t,放入当前所在的cur到m_node中,索引和mtr等->entry.init()初始化这个index_entry_t,所有物理结构信息初始化为0->flst_add_last(free_lst,cur,m_mtr)将初始化好的index_entry_t放入到链表free_lst中 OFFSET_INDEX_FREE_NODES.FLST_FIRST 指向第一个 index_entry_t ...
[PRIMARY KEY(column_name)] ) [table_options]; The template contains the following elements: CREATE TABLE. The statement to create a table. IF NOT EXISTS. An optional check that prevents an error if a table with the same name already exists. The exact table parameters are not checked and ...
To create a new table that is just like an existing table, use this statement: CREATETABLEnew_tableLIKEoriginal_table; The structure of the new table is the same as that of the original table, with a few exceptions:CREATETABLE…LIKEdoes not copy foreign key definitions, and it doesn’t ...