MySQL--索引面试题分析

小咪咪 2021-08-13 15:31 284阅读 0赞

### 索引面试题分析 ###

**建表及准备数据：**

CREATE TABLE test03(
    id INT PRIMARY KEY NOT NULL AUTO_INCREMENT,
    c1 CHAR(10),
    c2 CHAR(10),
    c3 CHAR(10),
    c4 CHAR(10),
    c5 CHAR(10)
    );
    
    INSERT INTO test03(c1,c2,c3,c4,c5) VALUES('a1','a2','a3','a4','a5');
    INSERT INTO test03(c1,c2,c3,c4,c5) VALUES('b1','b2','b3','b4','b5');
    INSERT INTO test03(c1,c2,c3,c4,c5) VALUES('c1','c2','c3','c4','c5');
    INSERT INTO test03(c1,c2,c3,c4,c5) VALUES('d1','d2','d3','d4','d5');
    INSERT INTO test03(c1,c2,c3,c4,c5) VALUES('e1','e2','e3','e4','e5');
    
    SELECT * FROM test03;

**创建索引：**

CREATE INDEX idx_test03_c1234 ON test03(c1,c2,c3,c4);

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![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NvbGRfX19wbGF5_size_16_color_FFFFFF_t_70 1]

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**原因：**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NvbGRfX19wbGF5_size_16_color_FFFFFF_t_70 3]

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