# 表达式索引 (B)
+ 当查询语句中的表达式与表达式索引中的表达式一致时，优化器可以为该查询选择使用表达式索引
```
SELECT lower(col1) FROM t;
SELECT * FROM t WHERE lower(col1) = "a";
SELECT * FROM t WHERE lower(col1) BETWEEN "a" AND "b";
SELECT * FROM t ORDER BY lower(col1);
SELECT min(col1) FROM t GROUP BY lower(col1);
```
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表达式索引
- 当查询语句中的表达式与表达式索引中的表达式一致时，优化器可以为该查询选择使用表达式索引
```
SELECT lower(col1) FROM t;
SELECT * FROM t WHERE lower(col1) = "a";
SELECT * FROM t WHERE lower(col1) BETWEEN "a" AND "b";
SELECT * FROM t ORDER BY lower(col1);
SELECT min(col1) FROM t GROUP BY lower(col1);
```