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select distinct col_name from table where a=X and b=Y and date(time)=‘xx-xx-xx‘;
执行时间 27.9772 秒
explain select distinct col_name from table where a=X and b=Y and date(time)=‘xx-xx-xx‘;
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | SIMPLE | access | ALL | NULL | NULL | NULL | NULL | 38714243 | Using where; Using temporary |
select distinct col_name from table where a=X and b=Y and time<‘xx-xx-xx‘;
执行时间 0.0038 秒
explain select distinct col_name from table where a=X and b=Y and time<‘xx-xx-xx‘;
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | SIMPLE | access | range | idx_access_dt | idx_access_dt | 4 | NULL | 1 | Using where; Using temporary |
select distinct col_name from table where a=X and b=Y and time=‘xx-xx-xx xx:xx:xx‘;
执行时间 0.0031 秒
explain select distinct col_name from table where a=X and b=Y and time=‘xx-xx-xx xx:xx:xx‘;
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | SIMPLE | access | ref | idx_access_dt | idx_access_dt | 4 | const | 82 | Using where; Using temporary |
参考：
http://www.cnitblog.com/aliyiyi08/archive/2008/09/09/48878.html
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原文地址：http://www.cnblogs.com/nerrissa/p/4214116.html
