Oracle执行计划Cost后缀含义咨询：879T代表879万亿吗？

Hey there, let's break down what those cost suffixes mean in your Oracle explain plans:

In Oracle's standard explain plan output, the suffixes for cost values follow standard metric abbreviations:

• K stands for thousand (10³)
• M stands for million (10⁶) – which matches your confirmed 37M = 37,000,000 in Explain Plan 1
• G stands for billion (10⁹)
• T stands for trillion (10¹²) – so your Explain Plan 2's 879T is absolutely 879 trillion, not 879 thousand (that would be written as 879K)

A cost of 879 trillion is extremely high – this usually indicates a problem with your query's execution plan, like outdated table/index statistics, missing critical indexes, or inefficient query logic that's forcing Oracle to do massive full scans or Cartesian joins.

Here are your original explain plan snippets for reference:

Explain Plan 1 #

-----------------------------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | E-Rows |E-Bytes|E-Temp | Cost (%CPU)| E-Time | OMem | 1Mem | Used-Mem |
-----------------------------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | | 37M(100)| | | | |
...
|* 36 | INDEX UNIQUE SCAN | ZX_ACCOUNTS_U2 | 1 | 36 | | 0 (0)| | 1025K| 1025K| |
-----------------------------------------------------------------------------------------------------------------------------------------------------------------

Explain Plan 2 #

-----------------------------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | E-Rows |E-Bytes|E-Temp | Cost (%CPU)| E-Time | OMem | 1Mem | Used-Mem |
-----------------------------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | | 879T(100)| | | | |
...
|* 39 | INDEX UNIQUE SCAN | ZX_ACCOUNTS_U2 | 1 | 36 | | 0 (0)| | 1025K| 1025K| |
-----------------------------------------------------------------------------------------------------------------------------------------------------------------

内容的提问来源于stack exchange，提问作者Migs