查找單列索引

Question

我試圖找出某列是否索引（本身）。換句話說，我不想拉多列的指數。

有人可以幫助我重寫這隻拉單列索引？

select table_name, index_name 
from information_schema.statistics 
where table_schema='schema' and table_name='table' and column_name='column'; 

Answer 1

您可以在子查詢中按照名稱對索引進行分組，然後選擇唯一的索引。

select index_name from 
    (select index_name, COUNT(*) as col_count 
    from information_schema.statistics 
    where table_schema='schema' and table_name='table' 
    group by index_name) as sub 
where col_count = 1 

---

您可能要添加到column_name內外select -list;和外部where條件。這可能會在這種情況下工作，因爲條件col_count = 1，但一般有一個簡單的列（不使用COUNT，MAX，...）在select -list未在group語句來上市，導致不可預測的行爲，參見sql antipattern。

Answer 2

無子選擇改寫...

這將爲特定的指數收益表和索引的名字它是一個單一的（不明）列

SELECT table_name, index_name 
FROM information_schema.statistics 
WHERE table_schema='schema' 
AND table_name='table' 
AND index_name = 'index' 
GROUP BY table_name, index_name 
HAVING COUNT(*) = 1; 

這是相同的在給定表中的所有單列索引

SELECT table_name, index_name 
FROM information_schema.statistics 
WHERE table_schema='schema' 
AND table_name='table' 
GROUP BY table_name, index_name 
HAVING COUNT(*) = 1; 

最後，所有單列索引在給定的數據庫

SELECT table_name, index_name 
FROM information_schema.statistics 
WHERE table_schema='schema' 
GROUP BY table_name, index_name 
HAVING COUNT(*) = 1;