问题描述
假设我有一个名为 't' 的表
Suppose I have a table named 't'
---------------
| key | value |
---------------
| 1 | abc |
| 2 | def |
---------------
考虑两个 MYSQL 查询
Consider two MYSQL queries
UPDATE t SET value='abc' WHERE key=1UPDATE t SET value='abc' WHERE key=3
执行这两个查询也会使受影响的行"为 0(即不更新任何行)，因为第一个查询是非更新更新，第二个查询是非匹配更新.
Executing both queries also give the 'affected rows' is 0 (That is, do NOT update any row) because first query is an non-updating update and second is an non-matching update.
有没有办法区分这两种情况?
Is there any way to distinguish these two cases?
推荐答案
如果你只想要'匹配'的行数(不再需要'改变'的行数)，你可以设置 CLIENT_FOUND_ROWS 如此处所述:
if you only want the number of 'matched' rows (and no longer the number of 'changed' rows), you can set CLIENT_FOUND_ROWS as described here:
http://dev.mysql.com/doc/refman/5.5/en/mysql-affected-rows.html
对于 UPDATE 语句，默认情况下受影响的行值是实际更改的行数.如果您指定 CLIENT_FOUND_ROWS连接到 mysqld 时标记 mysql_real_connect()，受影响的行值是找到"的行数；也就是说，匹配WHERE 子句.
For UPDATE statements, the affected-rows value by default is the number of rows actually changed. If you specify the CLIENT_FOUND_ROWS flag to mysql_real_connect() when connecting to mysqld, the affected-rows value is the number of rows "found"; that is, matched by the WHERE clause.
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