Mysql 中有哪些常用的SQL语句

今天就跟大家聊聊有关Mysql 中有哪些常用的SQL语句，可能很多人都不太了解，为了让大家更加了解，小编给大家总结了以下内容，希望大家根据这篇文章可以有所收获。

查询时间，友好提示

• timestamp 日期类型

  $sql = "select date_format(create_time, '%Y-%m-%d') as day from table_name";
  

• int 时间戳类型

  $sql = "select from_unixtime(create_time, '%Y-%m-%d') as day from table_name";

一个sql 返回多个总数

$sql = "select count(*) all, " ;

$sql .= " count(case when status = 1 then status end) status_1_num, ";

$sql .= " count(case when status = 2 then status end) status_2_num ";

$sql .= " from table_name";

Update Join / Delete Join

$sql = "update table_name_1 ";

$sql .= " inner join table_name_2 on table_name_1.id = table_name_2.uid ";

$sql .= " inner join table_name_3 on table_name_3.id = table_name_1.tid ";

$sql .= " set *** = *** ";

$sql .= " where *** ";

//delete join 同上。

替换某字段的内容的语句

$sql = "update table_name set content = REPLACE(content, 'aaa', 'bbb') ";

$sql .= " where (content like '%aaa%')";

获取表中某字段包含某字符串的数据

$sql = "SELECT * FROM `表名` WHERE LOCATE('关键字', 字段名) ";

查找表中多余的重复记录

• 单个字段

  $sql = "select * from 表名 where 字段名 in ";

  $sql .= "(select 字段名 from 表名 group by 字段名 having count(字段名) > 1 )";

• 多个字段

  $sql = "select * from 表名 别名 where (别名.字段1,别名.字段2) in ";

  $sql .= "(select 字段1,字段2 from 表名 group by 字段1,字段2 having count(*) > 1 )";

删除表中多余的重复记录(留id最小)

• 单个字段

  $sql = "delete from 表名 where 字段名 in ";

  $sql .= "(select 字段名 from 表名 group by 字段名 having count(字段名) > 1) ";

  $sql .= "and 主键ID not in ";

  $sql .= "(select min(主键ID) from 表名 group by 字段名 having count(字段名 )>1) ";

• 多个字段

  $sql = "delete from 表名 别名 where (别名.字段1,别名.字段2) in ";

  $sql .= "(select 字段1,字段2 from 表名 group by 字段1,字段2 having count(*) > 1) ";

  $sql .= "and 主键ID not in ";

  $sql .= "(select min(主键ID) from 表名 group by 字段1,字段2 having count(*)>1) ";

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