我有一個表像這樣是distinct(count(ColumnName))上索引on where子句所需的索引?
Subscribers
Id (PK, int)
OwnedBy (FK, int)
EmailAddress (varchar 50)
如果我這樣的查詢:
SELECT COUNT(DISTINCT(EmailAddress))
FROM Subscribers
WHERE Subscribers.OwnedBy = 67;
上有OwnedBy
列的索引。假設表格非常大,我是否應該索引EmailAddress
?我不關心寫入性能下降。
謝謝。你能否評論你的解決方案與Omesh提到的創建覆蓋索引? – Harper 2012-07-20 08:19:18
也許這會幫助你http://stackoverflow.com/questions/8213235/mysql-covering-vs-composite-vs-column-index – Horen 2012-07-20 08:27:31