优化这段sql:select `id`, `createDate`, `signalSourceSetValue`, `signalSourceTrueValue`, `receiveSignalAmplitude`, `transmitSignalAmplitude`, `simulationSetValue`, `simulationTrueValue`, `amplitude`, `frequency` from simulation_target_and_signal_source_truth_t <if test="frequency != null and frequency != '' "> where `createDate` = ( select Max(`createDate`) as 'createDate' from simulation_target_and_signal_source_truth_t where CONVERT (`frequency`,DECIMAL) = CONVERT( #{frequency},DECIMAL) ) </if> <if test="frequency == null or frequency == ''"> where `createDate` in ( SELECT DISTINCT FIRST_VALUE(`createDate`) over (PARTITION BY `frequency` ORDER BY `createDate`) AS 'createDate' FROM simulation_target_and_signal_source_truth_t ) </if>
时间: 2024-02-14 22:15:07 浏览: 20
首先,尝试将 `CONVERT (`frequency`,DECIMAL)` 改为 `CAST(frequency AS DECIMAL)`,这可以提高查询效率。
其次,可以把 `Max(`createDate`)` 改为 `SELECT TOP 1 createDate FROM ... ORDER BY createDate DESC` 的形式,也可以提高查询效率。这样查询最大的日期时不会返回所有日期,只会返回一个日期。
最后,如果 `frequency` 是一个经常被查询的字段,可以为该字段创建一个索引,以提高查询效率。
修改后的SQL如下:
```sql
SELECT `id`,
`createDate`,
`signalSourceSetValue`,
`signalSourceTrueValue`,
`receiveSignalAmplitude`,
`transmitSignalAmplitude`,
`simulationSetValue`,
`simulationTrueValue`,
`amplitude`,
`frequency`
FROM simulation_target_and_signal_source_truth_t
<if test="frequency != null and frequency != '' ">
WHERE `createDate` = (
SELECT TOP 1 createDate
FROM simulation_target_and_signal_source_truth_t
WHERE CAST(frequency AS DECIMAL) = CAST(#{frequency} AS DECIMAL)
ORDER BY createDate DESC
)
</if>
<if test="frequency == null or frequency == ''">
WHERE `createDate` IN (
SELECT DISTINCT
FIRST_VALUE(`createDate`) over (PARTITION BY `frequency` ORDER BY `createDate`) AS 'createDate'
FROM simulation_target_and_signal_source_truth_t
)
</if>
```
以上是一些简单的优化方法,根据实际情况可能还需要进一步的优化。