文章目录

• 1 概述
• 2 语法
• • 2.1 创建 create table
  • 2.2 修改 alter table
  • 2.3 清空 truncate table
  • 2.4 删除 drop table
• 3 扩展
• • 3.1 查询表、列、备注
  • 3.2 Mysql 外键详解（Foreign Key）

#mermaid-svg-moXx8z8B5U2m2sUw .label{font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family);fill:#333;color:#333}#mermaid-svg-moXx8z8B5U2m2sUw .label text{fill:#333}#mermaid-svg-moXx8z8B5U2m2sUw .node rect,#mermaid-svg-moXx8z8B5U2m2sUw .node circle,#mermaid-svg-moXx8z8B5U2m2sUw .node ellipse,#mermaid-svg-moXx8z8B5U2m2sUw .node polygon,#mermaid-svg-moXx8z8B5U2m2sUw .node path{fill:#ECECFF;stroke:#9370db;stroke-width:1px}#mermaid-svg-moXx8z8B5U2m2sUw .node .label{text-align:center;fill:#333}#mermaid-svg-moXx8z8B5U2m2sUw .node.clickable{cursor:pointer}#mermaid-svg-moXx8z8B5U2m2sUw .arrowheadPath{fill:#333}#mermaid-svg-moXx8z8B5U2m2sUw .edgePath .path{stroke:#333;stroke-width:1.5px}#mermaid-svg-moXx8z8B5U2m2sUw .flowchart-link{stroke:#333;fill:none}#mermaid-svg-moXx8z8B5U2m2sUw .edgeLabel{background-color:#e8e8e8;text-align:center}#mermaid-svg-moXx8z8B5U2m2sUw .edgeLabel rect{opacity:0.9}#mermaid-svg-moXx8z8B5U2m2sUw .edgeLabel span{color:#333}#mermaid-svg-moXx8z8B5U2m2sUw .cluster rect{fill:#ffffde;stroke:#aa3;stroke-width:1px}#mermaid-svg-moXx8z8B5U2m2sUw .cluster text{fill:#333}#mermaid-svg-moXx8z8B5U2m2sUw div.mermaidTooltip{position:absolute;text-align:center;max-width:200px;padding:2px;font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family);font-size:12px;background:#ffffde;border:1px solid #aa3;border-radius:2px;pointer-events:none;z-index:100}#mermaid-svg-moXx8z8B5U2m2sUw .actor{stroke:#ccf;fill:#ECECFF}#mermaid-svg-moXx8z8B5U2m2sUw text.actor>tspan{fill:#000;stroke:none}#mermaid-svg-moXx8z8B5U2m2sUw .actor-line{stroke:grey}#mermaid-svg-moXx8z8B5U2m2sUw .messageLine0{stroke-width:1.5;stroke-dasharray:none;stroke:#333}#mermaid-svg-moXx8z8B5U2m2sUw .messageLine1{stroke-width:1.5;stroke-dasharray:2, 2;stroke:#333}#mermaid-svg-moXx8z8B5U2m2sUw #arrowhead path{fill:#333;stroke:#333}#mermaid-svg-moXx8z8B5U2m2sUw .sequenceNumber{fill:#fff}#mermaid-svg-moXx8z8B5U2m2sUw #sequencenumber{fill:#333}#mermaid-svg-moXx8z8B5U2m2sUw #crosshead path{fill:#333;stroke:#333}#mermaid-svg-moXx8z8B5U2m2sUw .messageText{fill:#333;stroke:#333}#mermaid-svg-moXx8z8B5U2m2sUw .labelBox{stroke:#ccf;fill:#ECECFF}#mermaid-svg-moXx8z8B5U2m2sUw .labelText,#mermaid-svg-moXx8z8B5U2m2sUw .labelText>tspan{fill:#000;stroke:none}#mermaid-svg-moXx8z8B5U2m2sUw .loopText,#mermaid-svg-moXx8z8B5U2m2sUw .loopText>tspan{fill:#000;stroke:none}#mermaid-svg-moXx8z8B5U2m2sUw .loopLine{stroke-width:2px;stroke-dasharray:2, 2;stroke:#ccf;fill:#ccf}#mermaid-svg-moXx8z8B5U2m2sUw .note{stroke:#aa3;fill:#fff5ad}#mermaid-svg-moXx8z8B5U2m2sUw .noteText,#mermaid-svg-moXx8z8B5U2m2sUw .noteText>tspan{fill:#000;stroke:none}#mermaid-svg-moXx8z8B5U2m2sUw .activation0{fill:#f4f4f4;stroke:#666}#mermaid-svg-moXx8z8B5U2m2sUw .activation1{fill:#f4f4f4;stroke:#666}#mermaid-svg-moXx8z8B5U2m2sUw .activation2{fill:#f4f4f4;stroke:#666}#mermaid-svg-moXx8z8B5U2m2sUw .mermaid-main-font{font-family:"trebuchet ms", verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-moXx8z8B5U2m2sUw .section{stroke:none;opacity:0.2}#mermaid-svg-moXx8z8B5U2m2sUw .section0{fill:rgba(102,102,255,0.49)}#mermaid-svg-moXx8z8B5U2m2sUw .section2{fill:#fff400}#mermaid-svg-moXx8z8B5U2m2sUw .section1,#mermaid-svg-moXx8z8B5U2m2sUw .section3{fill:#fff;opacity:0.2}#mermaid-svg-moXx8z8B5U2m2sUw .sectionTitle0{fill:#333}#mermaid-svg-moXx8z8B5U2m2sUw .sectionTitle1{fill:#333}#mermaid-svg-moXx8z8B5U2m2sUw .sectionTitle2{fill:#333}#mermaid-svg-moXx8z8B5U2m2sUw .sectionTitle3{fill:#333}#mermaid-svg-moXx8z8B5U2m2sUw .sectionTitle{text-anchor:start;font-size:11px;text-height:14px;font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-moXx8z8B5U2m2sUw .grid .tick{stroke:#d3d3d3;opacity:0.8;shape-rendering:crispEdges}#mermaid-svg-moXx8z8B5U2m2sUw .grid .tick text{font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-moXx8z8B5U2m2sUw .grid path{stroke-width:0}#mermaid-svg-moXx8z8B5U2m2sUw .today{fill:none;stroke:red;stroke-width:2px}#mermaid-svg-moXx8z8B5U2m2sUw .task{stroke-width:2}#mermaid-svg-moXx8z8B5U2m2sUw .taskText{text-anchor:middle;font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-moXx8z8B5U2m2sUw .taskText:not([font-size]){font-size:11px}#mermaid-svg-moXx8z8B5U2m2sUw .taskTextOutsideRight{fill:#000;text-anchor:start;font-size:11px;font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-moXx8z8B5U2m2sUw .taskTextOutsideLeft{fill:#000;text-anchor:end;font-size:11px}#mermaid-svg-moXx8z8B5U2m2sUw .task.clickable{cursor:pointer}#mermaid-svg-moXx8z8B5U2m2sUw .taskText.clickable{cursor:pointer;fill:#003163 !important;font-weight:bold}#mermaid-svg-moXx8z8B5U2m2sUw .taskTextOutsideLeft.clickable{cursor:pointer;fill:#003163 !important;font-weight:bold}#mermaid-svg-moXx8z8B5U2m2sUw .taskTextOutsideRight.clickable{cursor:pointer;fill:#003163 !important;font-weight:bold}#mermaid-svg-moXx8z8B5U2m2sUw .taskText0,#mermaid-svg-moXx8z8B5U2m2sUw .taskText1,#mermaid-svg-moXx8z8B5U2m2sUw .taskText2,#mermaid-svg-moXx8z8B5U2m2sUw .taskText3{fill:#fff}#mermaid-svg-moXx8z8B5U2m2sUw .task0,#mermaid-svg-moXx8z8B5U2m2sUw .task1,#mermaid-svg-moXx8z8B5U2m2sUw .task2,#mermaid-svg-moXx8z8B5U2m2sUw .task3{fill:#8a90dd;stroke:#534fbc}#mermaid-svg-moXx8z8B5U2m2sUw .taskTextOutside0,#mermaid-svg-moXx8z8B5U2m2sUw .taskTextOutside2{fill:#000}#mermaid-svg-moXx8z8B5U2m2sUw .taskTextOutside1,#mermaid-svg-moXx8z8B5U2m2sUw .taskTextOutside3{fill:#000}#mermaid-svg-moXx8z8B5U2m2sUw .active0,#mermaid-svg-moXx8z8B5U2m2sUw .active1,#mermaid-svg-moXx8z8B5U2m2sUw .active2,#mermaid-svg-moXx8z8B5U2m2sUw .active3{fill:#bfc7ff;stroke:#534fbc}#mermaid-svg-moXx8z8B5U2m2sUw .activeText0,#mermaid-svg-moXx8z8B5U2m2sUw .activeText1,#mermaid-svg-moXx8z8B5U2m2sUw .activeText2,#mermaid-svg-moXx8z8B5U2m2sUw .activeText3{fill:#000 !important}#mermaid-svg-moXx8z8B5U2m2sUw .done0,#mermaid-svg-moXx8z8B5U2m2sUw .done1,#mermaid-svg-moXx8z8B5U2m2sUw .done2,#mermaid-svg-moXx8z8B5U2m2sUw .done3{stroke:grey;fill:#d3d3d3;stroke-width:2}#mermaid-svg-moXx8z8B5U2m2sUw .doneText0,#mermaid-svg-moXx8z8B5U2m2sUw .doneText1,#mermaid-svg-moXx8z8B5U2m2sUw .doneText2,#mermaid-svg-moXx8z8B5U2m2sUw .doneText3{fill:#000 !important}#mermaid-svg-moXx8z8B5U2m2sUw .crit0,#mermaid-svg-moXx8z8B5U2m2sUw .crit1,#mermaid-svg-moXx8z8B5U2m2sUw .crit2,#mermaid-svg-moXx8z8B5U2m2sUw .crit3{stroke:#f88;fill:red;stroke-width:2}#mermaid-svg-moXx8z8B5U2m2sUw .activeCrit0,#mermaid-svg-moXx8z8B5U2m2sUw .activeCrit1,#mermaid-svg-moXx8z8B5U2m2sUw .activeCrit2,#mermaid-svg-moXx8z8B5U2m2sUw .activeCrit3{stroke:#f88;fill:#bfc7ff;stroke-width:2}#mermaid-svg-moXx8z8B5U2m2sUw .doneCrit0,#mermaid-svg-moXx8z8B5U2m2sUw .doneCrit1,#mermaid-svg-moXx8z8B5U2m2sUw .doneCrit2,#mermaid-svg-moXx8z8B5U2m2sUw .doneCrit3{stroke:#f88;fill:#d3d3d3;stroke-width:2;cursor:pointer;shape-rendering:crispEdges}#mermaid-svg-moXx8z8B5U2m2sUw .milestone{transform:rotate(45deg) scale(0.8, 0.8)}#mermaid-svg-moXx8z8B5U2m2sUw .milestoneText{font-style:italic}#mermaid-svg-moXx8z8B5U2m2sUw .doneCritText0,#mermaid-svg-moXx8z8B5U2m2sUw .doneCritText1,#mermaid-svg-moXx8z8B5U2m2sUw .doneCritText2,#mermaid-svg-moXx8z8B5U2m2sUw .doneCritText3{fill:#000 !important}#mermaid-svg-moXx8z8B5U2m2sUw .activeCritText0,#mermaid-svg-moXx8z8B5U2m2sUw .activeCritText1,#mermaid-svg-moXx8z8B5U2m2sUw .activeCritText2,#mermaid-svg-moXx8z8B5U2m2sUw .activeCritText3{fill:#000 !important}#mermaid-svg-moXx8z8B5U2m2sUw .titleText{text-anchor:middle;font-size:18px;fill:#000;font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-moXx8z8B5U2m2sUw g.classGroup text{fill:#9370db;stroke:none;font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family);font-size:10px}#mermaid-svg-moXx8z8B5U2m2sUw g.classGroup text .title{font-weight:bolder}#mermaid-svg-moXx8z8B5U2m2sUw g.clickable{cursor:pointer}#mermaid-svg-moXx8z8B5U2m2sUw g.classGroup rect{fill:#ECECFF;stroke:#9370db}#mermaid-svg-moXx8z8B5U2m2sUw g.classGroup line{stroke:#9370db;stroke-width:1}#mermaid-svg-moXx8z8B5U2m2sUw .classLabel .box{stroke:none;stroke-width:0;fill:#ECECFF;opacity:0.5}#mermaid-svg-moXx8z8B5U2m2sUw .classLabel .label{fill:#9370db;font-size:10px}#mermaid-svg-moXx8z8B5U2m2sUw .relation{stroke:#9370db;stroke-width:1;fill:none}#mermaid-svg-moXx8z8B5U2m2sUw .dashed-line{stroke-dasharray:3}#mermaid-svg-moXx8z8B5U2m2sUw #compositionStart{fill:#9370db;stroke:#9370db;stroke-width:1}#mermaid-svg-moXx8z8B5U2m2sUw #compositionEnd{fill:#9370db;stroke:#9370db;stroke-width:1}#mermaid-svg-moXx8z8B5U2m2sUw #aggregationStart{fill:#ECECFF;stroke:#9370db;stroke-width:1}#mermaid-svg-moXx8z8B5U2m2sUw #aggregationEnd{fill:#ECECFF;stroke:#9370db;stroke-width:1}#mermaid-svg-moXx8z8B5U2m2sUw #dependencyStart{fill:#9370db;stroke:#9370db;stroke-width:1}#mermaid-svg-moXx8z8B5U2m2sUw #dependencyEnd{fill:#9370db;stroke:#9370db;stroke-width:1}#mermaid-svg-moXx8z8B5U2m2sUw #extensionStart{fill:#9370db;stroke:#9370db;stroke-width:1}#mermaid-svg-moXx8z8B5U2m2sUw #extensionEnd{fill:#9370db;stroke:#9370db;stroke-width:1}#mermaid-svg-moXx8z8B5U2m2sUw .commit-id,#mermaid-svg-moXx8z8B5U2m2sUw .commit-msg,#mermaid-svg-moXx8z8B5U2m2sUw .branch-label{fill:lightgrey;color:lightgrey;font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-moXx8z8B5U2m2sUw .pieTitleText{text-anchor:middle;font-size:25px;fill:#000;font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-moXx8z8B5U2m2sUw .slice{font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-moXx8z8B5U2m2sUw g.stateGroup text{fill:#9370db;stroke:none;font-size:10px;font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-moXx8z8B5U2m2sUw g.stateGroup text{fill:#9370db;fill:#333;stroke:none;font-size:10px}#mermaid-svg-moXx8z8B5U2m2sUw g.statediagram-cluster .cluster-label text{fill:#333}#mermaid-svg-moXx8z8B5U2m2sUw g.stateGroup .state-title{font-weight:bolder;fill:#000}#mermaid-svg-moXx8z8B5U2m2sUw g.stateGroup rect{fill:#ECECFF;stroke:#9370db}#mermaid-svg-moXx8z8B5U2m2sUw g.stateGroup line{stroke:#9370db;stroke-width:1}#mermaid-svg-moXx8z8B5U2m2sUw .transition{stroke:#9370db;stroke-width:1;fill:none}#mermaid-svg-moXx8z8B5U2m2sUw .stateGroup .composit{fill:white;border-bottom:1px}#mermaid-svg-moXx8z8B5U2m2sUw .stateGroup .alt-composit{fill:#e0e0e0;border-bottom:1px}#mermaid-svg-moXx8z8B5U2m2sUw .state-note{stroke:#aa3;fill:#fff5ad}#mermaid-svg-moXx8z8B5U2m2sUw .state-note text{fill:black;stroke:none;font-size:10px}#mermaid-svg-moXx8z8B5U2m2sUw .stateLabel .box{stroke:none;stroke-width:0;fill:#ECECFF;opacity:0.7}#mermaid-svg-moXx8z8B5U2m2sUw .edgeLabel text{fill:#333}#mermaid-svg-moXx8z8B5U2m2sUw .stateLabel text{fill:#000;font-size:10px;font-weight:bold;font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-moXx8z8B5U2m2sUw .node circle.state-start{fill:black;stroke:black}#mermaid-svg-moXx8z8B5U2m2sUw .node circle.state-end{fill:black;stroke:white;stroke-width:1.5}#mermaid-svg-moXx8z8B5U2m2sUw #statediagram-barbEnd{fill:#9370db}#mermaid-svg-moXx8z8B5U2m2sUw .statediagram-cluster rect{fill:#ECECFF;stroke:#9370db;stroke-width:1px}#mermaid-svg-moXx8z8B5U2m2sUw .statediagram-cluster rect.outer{rx:5px;ry:5px}#mermaid-svg-moXx8z8B5U2m2sUw .statediagram-state .divider{stroke:#9370db}#mermaid-svg-moXx8z8B5U2m2sUw .statediagram-state .title-state{rx:5px;ry:5px}#mermaid-svg-moXx8z8B5U2m2sUw .statediagram-cluster.statediagram-cluster .inner{fill:white}#mermaid-svg-moXx8z8B5U2m2sUw .statediagram-cluster.statediagram-cluster-alt .inner{fill:#e0e0e0}#mermaid-svg-moXx8z8B5U2m2sUw .statediagram-cluster .inner{rx:0;ry:0}#mermaid-svg-moXx8z8B5U2m2sUw .statediagram-state rect.basic{rx:5px;ry:5px}#mermaid-svg-moXx8z8B5U2m2sUw .statediagram-state rect.divider{stroke-dasharray:10,10;fill:#efefef}#mermaid-svg-moXx8z8B5U2m2sUw .note-edge{stroke-dasharray:5}#mermaid-svg-moXx8z8B5U2m2sUw .statediagram-note rect{fill:#fff5ad;stroke:#aa3;stroke-width:1px;rx:0;ry:0}:root{--mermaid-font-family: '"trebuchet ms", verdana, arial';--mermaid-font-family: "Comic Sans MS", "Comic Sans", cursive}#mermaid-svg-moXx8z8B5U2m2sUw .error-icon{fill:#522}#mermaid-svg-moXx8z8B5U2m2sUw .error-text{fill:#522;stroke:#522}#mermaid-svg-moXx8z8B5U2m2sUw .edge-thickness-normal{stroke-width:2px}#mermaid-svg-moXx8z8B5U2m2sUw .edge-thickness-thick{stroke-width:3.5px}#mermaid-svg-moXx8z8B5U2m2sUw .edge-pattern-solid{stroke-dasharray:0}#mermaid-svg-moXx8z8B5U2m2sUw .edge-pattern-dashed{stroke-dasharray:3}#mermaid-svg-moXx8z8B5U2m2sUw .edge-pattern-dotted{stroke-dasharray:2}#mermaid-svg-moXx8z8B5U2m2sUw .marker{fill:#333}#mermaid-svg-moXx8z8B5U2m2sUw .marker.cross{stroke:#333}:root { --mermaid-font-family: "trebuchet ms", verdana, arial;}#mermaid-svg-moXx8z8B5U2m2sUw {color: rgba(0, 0, 0, 0.75);font: ;}

create table student_info (sno         int unsigned auto_increment comment '学号',name        varchar(50) not null comment '姓名',create_date date not null comment '创建时间',primary key(sno)
) engine=innodb default charset=utf8 comment '学生信息表';

1. 主键相关(1) unsigned auto_increment: 从 1 自增，常用于主键(2) primary key: 定义主键2. 默认设置 -- 一般无需显示设置，默认即可(1) engine=innodb：存储引擎（默认 innodb）-- show engines;(2) default charset=utf8：字符编码（默认 utf8）-- show variables like 'character_set_%';
/*
3. 说明：一般创建表时，均要添加以下字段create_user varchar(50) not null comment '创建人',create_date date not null comment '创建时间',update_user varchar(50) not null comment '更新人',update_date date not null comment '更新时间'*/

-- '增加' 一列或者多列
alter table student_info add sex varchar(10) comment '性别';
alter table student_info add (id_type varchar(10) comment '证件类型', id_no int comment '证件号码');
---- 按指定位置添加列 before | after
alter table student_info add age int comment '年龄' after sex;-- '修改' 一列或者多列
---- 数据类型
alter table student_info modify sex varchar(20) not null;
---- 列名
alter table student_info rename column sex to new_sex;
---- 表名
alter table student_info rename to new_student_info ;
alter table new_student_info rename to student_info;

-- 仅清空表数据
truncate table student_info;

-- 删除表结构
drop table student_info;

-- 查询表
select t.table_schema,t.table_name,t.table_commentfrom information_schema.tables twhere t.table_name = 'student_info';-- 查询列
select c.table_schema,c.ordinal_position,c.column_name,c.column_type,c.column_commentfrom information_schema.columns cwhere c.table_name = 'student_info'order by c.ordinal_position;