Select 后接查询展示的字段，* 代表所有字段，from后接从哪张表里查找，where后面接查询条件。
例1：从fail_info 表中查找日期为1月13号的不良情况。
Select * from fail_info where line_date='1月3号';
例2：Select fail_name from fail_info where fail_category='功能';
Group by 后接分组字段，distinct用于字段去重，后接需要去重的字段。如查询各分类的不良数量。
Select distinct fail_category,sum(fail_qty) from fail_info group by fail_category;
having 是分组之后指定查询条件，如查询分类功能和外观的不良数量。
Select distinct fail_category,sum(fail_qty) from fail_info group by fail_category having fail_category not in(‘尺寸’);
注意where用于分组前指定条件，having用于分组后指定条件。例如：
Select distinct fail_category,sum(fail_qty) from fail_info where line_date=’1月3号’ group by fail_category;
order by 用于排序，后接指定的排序字段，limit用于指定展示的行。例如：
根据不良数量排序，升序，展示前5条数据。
select * from fail_info order by fail_qty limit 5;
根据不良数量排序，降序，展示前5条数据。
select * from fail_info order by fail_qty desc limit 5;
根据不良数量排序，降序，跳过前2条展示前3条数据。
Select * from fail_info order by fail_qty desc limit 2,3;
GROUP_CONCAT 将查询字段合并展示，如按分类查询不良产生的日期。例如：
select GROUP_CONCAT(distinct line_date) as ‘不良日期’,fail_category from fail_info group by fail_category;
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