优化语句select collectite0_.ID as ID48_, collectite0_.COLLECT_TIME as COLLECT2_48_, collectite0_.COLLECT_TYPE as COLLECT3_48_, collectite0_.COLLECT_VALUE as COLLECT4_48_, collectite0_.DATA_EXTRACTION_TYPE as DATA5_48_, collectite0_.HOST_ID as HOST6_48_ from G2_T_COLLECT_ITEM collectite0_ where collectite0_.COLLECT_TYPE='memory' and collectite0_.HOST_ID='ff808081632a5fb8016347f5fa4f7c4a' order by collectite0_.COLLECT_TIME desc limit 5;

这条 SQL 语句可以进行如下优化：

1. 创建索引：在 `G2_T_COLLECT_ITEM` 表上创建一个联合索引，包含 `COLLECT_TYPE` 和 `HOST_ID` 字段，可以加速筛选条件中的两个字段。

2. 精简查询字段：只查询需要的字段，避免查询不必要的字段，可以减少查询时间和网络带宽的消耗。

最终优化后的 SQL 语句如下：

SELECT collectite0_.ID, collectite0_.COLLECT_TIME, collectite0_.COLLECT_VALUE
FROM G2_T_COLLECT_ITEM collectite0_
WHERE collectite0_.COLLECT_TYPE='memory' AND collectite0_.HOST_ID='ff808081632a5fb8016347f5fa4f7c4a'
ORDER BY collectite0_.COLLECT_TIME DESC
LIMIT 5;

希望对你有所帮助！