mysql笔记

创建数据库

create database dbtest1

查

查询数据库通用语法：

select columnName,columnName1 from dbname.tablename [where clause] [order by] [limit N];

查看表格所有列：

select * from dbname.tablename;

查看某一列和：

select SUM(columnName) from dbname.tableName;

多表联合查找

select table1.column1,table1.column2 from table1 left join table2 on table1.column3=table2.column3 where table1.column4='test';//left join以左表为主，获取左表所有记录，即使右表没有匹配记录，
right join相反，以右表为主，获取右表所有记录，inner join则获取量表中字段完全匹配关系的记录

单一条件联合查找

select * from table 1 where column1 = (select column1 from table2 where column3>0);

条件查找之if语句

select ( case
    when column1 + column2 = column3 then 'true'
        when column1 + column2 != column3 then 'false'
end) as result from table1 where column>0;

查看表行数

select count(*) from table1;

排序，限行数

select * from table1 order by column1 desc limit 10; //按column1倒叙排列,取前10行