整表更新

Question

目前我们使用 MySQL。

我们有带有空间索引的表（所以没有 InnoDB），并且每 x 秒更新一次整个表（将对象从一个地方移动到另一个地方）。

目前我们正在做：

UPDATE LOW_PRIORITY IGNORE `table`
SET `column1` = CASE `column2`
              WHEN 1 THEN ...
              WHEN 2 THEN ...
              WHEN 3 THEN ...
              ...
              ELSE `column1`
              END;

但是随着行数的增加，它会变得非常痛苦。有没有更好的方法来更新整个表？也许我们应该切换到其他数据库（PostGIS、NoSQL）？

对此有什么想法吗？

Answer 1

一次更新多行的最佳方法是：

• 创建临时表
• 用大 INSERT 填充（主键，新值）
• UPDATE table JOIN temptable USING（主键）SET table.oldvalue=temptable.newvalue

更新：

create table test ( id integer primary key, p point not null );
insert into test (id,p) select id, POINT( id%100, floor(id/100) ) from serie limit 10000;
alter table test add spatial index spi (p);
select id, AsText(p) from test;

+----+-------------+
| id | AsText(p)   |
+----+-------------+
|  1 | POINT(1 0)  |
|  2 | POINT(2 0)  |
|  3 | POINT(3 0)  |
...

|  98 | POINT(98 0) |
|  99 | POINT(99 0) |
| 100 | POINT(0 1)  |
| 101 | POINT(1 1)  |
...

|  9999 | POINT(99 99) |
| 10000 | POINT(0 100) |
+-------+--------------+


EXPLAIN SELECT id,AsText(p) from test where Contains( GeomFromText('POLYGON((0 0,0 10,10 10,10 0,0 0))'), p );
+----+-------------+-------+-------+---------------+------+---------+------+------+-------------+
| id | select_type | table | type  | possible_keys | key  | key_len | ref  | rows | Extra       |
+----+-------------+-------+-------+---------------+------+---------+------+------+-------------+
|  1 | SIMPLE      | test  | range | spi           | spi  | 34      | NULL |  112 | Using where |
+----+-------------+-------+-------+---------------+------+---------+------+------+-------------+

create temporary table test2 ( id integer primary key, p point not null );
insert into test2 (id,p) select id, POINT( 1+(id%100), 1+floor(id/100) ) from serie limit 10000;
update test, test2 set test.p=test2.p where test.id=test2.id;

EXPLAIN SELECT id,AsText(p) from test where Contains( GeomFromText('POLYGON((0 0,0 10,10 10,10 0,0 0))'), p );
+----+-------------+-------+-------+---------------+------+---------+------+------+-------------+
| id | select_type | table | type  | possible_keys | key  | key_len | ref  | rows | Extra       |
+----+-------------+-------+-------+---------------+------+---------+------+------+-------------+
|  1 | SIMPLE      | test  | range | spi           | spi  | 34      | NULL |  102 | Using where |
+----+-------------+-------+-------+---------------+------+---------+------+------+-------------+

这里没问题（MySQL 5.1.41）