一个表 有个联合索引emp_no,title,from_date 1
1.1 SELECT * FROM tbl WHERE title ='Senior' and emp_no < '10001' //这里使用到了最左前缀的emp_no索引
1.2 SELECT * FROM tbl WHERE title ='Senior' and emp_no like '10001' //这里没有使用到索引同样都是范围查询 为什么第二个没有使用emp_no索引?2
2.1SELECT * FROM tbl
WHERE emp_no BETWEEN '10001' AND '10010'
AND title='Senior Engineer'
AND from_date BETWEEN '1986-01-01' AND '1986-12-31';用到了所有索引
2.2
SELECT * FROM tbl
WHERE emp_no BETWEEN '10001' AND '10010'
AND title='Senior Engineer'
AND from_date > '1986-01-01' AND from_date<'1986-12-31';只用到emp_no的索引为什么? 第二个的title怎么没用到?
1.1 SELECT * FROM tbl WHERE title ='Senior' and emp_no < '10001' //这里使用到了最左前缀的emp_no索引
1.2 SELECT * FROM tbl WHERE title ='Senior' and emp_no like '10001' //这里没有使用到索引同样都是范围查询 为什么第二个没有使用emp_no索引?2
2.1SELECT * FROM tbl
WHERE emp_no BETWEEN '10001' AND '10010'
AND title='Senior Engineer'
AND from_date BETWEEN '1986-01-01' AND '1986-12-31';用到了所有索引
2.2
SELECT * FROM tbl
WHERE emp_no BETWEEN '10001' AND '10010'
AND title='Senior Engineer'
AND from_date > '1986-01-01' AND from_date<'1986-12-31';只用到emp_no的索引为什么? 第二个的title怎么没用到?
explain SELECT * FROM tbl WHERE title ='Senior' and emp_no < '10001' ;explain SELECT * FROM tbl WHERE title ='Senior' and emp_no like '10001'
1 explain:
2 explain: