TbUser one = new LambdaQueryChainWrapper<>(tbUserMapper) .select(TbUser::getUserId, TbUser::getNickname) .eq(TbUser::getUserId, 1239563848215904258L).one();
逻辑删除的字段是deleted
但是我发现执行的时候打印的SQL是
SELECT user_id,nickname FROM tb_user WHERE deleted=0 AND user_id = ?
deleted条件自动放在了最前面，这样对大数据量查询性能不会有负面影响吗？
2020-03-16
以本人愚见，MySQL对语句的执行是有优化的。MySQL会对执行的语句进行处理，生成多种执行方案，然后选取成本最低的方案。下面是两条语句的执行计划：
mysql> explain SELECT * FROM user WHERE id = 1088248166370832385 and deleted =0\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: user
partitions: NULL
type: const
possible_keys: PRIMARY
key: PRIMARY
key_len: 8
ref: const
rows: 1
filtered: 100.00
Extra: NULL
mysql> explain SELECT * FROM user WHERE deleted=0 AND id = 1088248166370832385\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: user
partitions: NULL
type: const
possible_keys: PRIMARY
key: PRIMARY
key_len: 8
ref: const
rows: 1
filtered: 100.00
Extra: NULL
两个的执行计划是一样的。它们的效率应该会相等吧。
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