mysql - 如果 Alter 表中的单个索引是多列索引的一部分，则不会添加它

Question

到目前为止，我在存储过程中有这个:

IF NOT EXISTS(SELECT 1 FROM information_schema.statistics WHERE TABLE_SCHEMA=DATABASE()
        AND TABLE_NAME= 'food'  AND (INDEX_NAME='ix_meat' OR COLUMN_NAME='meat')
    )
THEN
    CREATE INDEX ix_meat ON food (meat);
END IF; 


IF NOT EXISTS(SELECT 1 FROM information_schema.statistics WHERE TABLE_SCHEMA=DATABASE()
        AND TABLE_NAME= 'food'  AND (INDEX_NAME='ix_greens' OR COLUMN_NAME='greens')
    )
THEN
    CREATE INDEX ix_greens ON food(greens);
END IF; 

食物中除主要成分外的其余成分是:

fruits, portion, gender, weight

如果这些列上没有单个索引，或者它们中的任何一个是多列索引的一部分但在右侧，例如(性别，绿色)，我只想添加一个索引。为了确保单列索引不存在，我需要对该列进行行计数检查。我该如何修改这个脚本来做到这一点？

Answer 1

使用seq_in_index列来告知该列在索引中的位置。您想要添加索引，除非它是索引中的第一列。

IF NOT EXISTS(SELECT 1 FROM information_schema.statistics WHERE TABLE_SCHEMA=DATABASE()
        AND TABLE_NAME= 'food'  AND (INDEX_NAME='ix_meat' OR (COLUMN_NAME='meat' AND SEQ_IN_INDEX = 1))
    )
THEN
    CREATE INDEX ix_meat ON food (meat);
END IF; 


IF NOT EXISTS(SELECT 1 FROM information_schema.statistics WHERE TABLE_SCHEMA=DATABASE()
        AND TABLE_NAME= 'food'  AND (INDEX_NAME='ix_greens' OR (COLUMN_NAME='greens' AND SEQ_IN_INDEX = 1))
    )
THEN
    CREATE INDEX ix_greens ON food(greens);
END IF;