在 MySQL 中选择 TOP

Question

我怎样才能在 MySQL 中做到这一点？

SELECT TOP 50 PERCENT * FROM table

在不运行单独查询的情况下（如果可能），最简单的方法是什么？

Answer 1

MySQL 中没有 TOP n PERCENT 语法。

你将不得不模仿它如下

首先这里是一个示例表

mysql> use test
Database changed
mysql> drop table if exists mytable;
Query OK, 0 rows affected (0.06 sec)

mysql> create table mytable (id int not null auto_increment primary key);
Query OK, 0 rows affected (0.06 sec)

mysql> insert into mytable values (),(),(),(),(),(),(),(),(),();
Query OK, 10 rows affected (0.07 sec)
Records: 10  Duplicates: 0  Warnings: 0

mysql> select * from mytable;
+----+
| id |
+----+
|  1 |
|  2 |
|  3 |
|  4 |
|  5 |
|  6 |
|  7 |
|  8 |
|  9 |
| 10 |
+----+
10 rows in set (0.01 sec)

mysql>

您可以使用以下代码模拟它：

set @percent = 50;
select floor(count(1) * @percent / 100.0) into @pct from mytable;
set @sqlstmt = concat('select * from mytable limit ',@pct);
prepare stmt from @sqlstmt;
execute stmt;
deallocate prepare stmt;

这是执行的代码：

mysql> set @percent = 50;
Query OK, 0 rows affected (0.00 sec)

mysql> select floor(count(1) * @percent / 100.0) into @pct from mytable;
Query OK, 1 row affected (0.00 sec)

mysql> set @sqlstmt = concat('select * from mytable limit ',@pct);
Query OK, 0 rows affected (0.00 sec)

mysql> prepare stmt from @sqlstmt;
Query OK, 0 rows affected (0.01 sec)
Statement prepared

mysql> execute stmt;
+----+
| id |
+----+
|  1 |
|  2 |
|  3 |
|  4 |
|  5 |
+----+
5 rows in set (0.00 sec)

mysql> deallocate prepare stmt;
Query OK, 0 rows affected (0.00 sec)

mysql>

试一试 ！！！