[英]Indexing a table for better performance by a query
What index/indexes would you recommend to be created on the table for making the following type of query more efficient: 建议您在表上创建哪些索引,以提高以下类型的查询的效率:
SELECT MAX(val1)
FROM table
WHERE val2 = 'x' OR val3 = 'y'
x and y are of course variable. x和y当然是可变的。 val2 and val3 are almost always unique, some duplicates may occur. val2和val3几乎总是唯一的,可能会出现一些重复。
have an index on val2
+ val1
and another on val3
+ val1
and write query like: 在val2
+ val1
上有一个索引,在val3
+ val1
上有另一个,并编写如下查询:
SELECT MAX(val1)
FROM (SELECT max(val1) FROM table where val2 = 'x'
UNION ALL
SELECT max(val1) FROM table val3 = 'y'
) dt
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