MySQL select语句 汇总

# 选择
SELECT cpu FROM laptop

# 去重
SELECT DISTINCT cpu FROM laptop

# 最多取几条
SELECT id FROM laptop
LIMIT 5

# 从第22行开始取五条
SELECT id FROM laptop
LIMIT 21, 5

# 排序并且降序，升序去掉desc
SELECT `memory` FROM laptop
ORDER BY `memory` DESC 

# 下面都是where的操作符
SELECT * FROM laptop
WHERE laptop.disk='512GB'

SELECT * FROM laptop
WHERE laptop.disk<>'512GB'

SELECT * FROM laptop
WHERE laptop.disk!='512GB'

SELECT * FROM laptop
WHERE laptop.memory>8

SELECT * FROM laptop
WHERE laptop.memory>=8

SELECT * FROM laptop
WHERE laptop.memory<16

SELECT * FROM laptop
WHERE laptop.memory<8

# 两值之间，还有and or not等等
SELECT * FROM laptop
WHERE laptop.memory BETWEEN 8 AND 16

# 通配符%
SELECT * FROM laptop
WHERE laptop.cpu LIKE '%i%'

# 通配符_
SELECT * FROM laptop
WHERE laptop.cpu LIKE '_ayzen'

# 正则表达式
# 列数据中包含某个字符串
SELECT cpu FROM laptop
WHERE cpu REGEXP 'i'

# 在上面的基础上包含多个字符串
SELECT laptop.disk FROM laptop
WHERE laptop.disk REGEXP '512|1T'

# 中括号括起来
SELECT laptop.disk FROM laptop
WHERE laptop.disk REGEXP '[12]T'

# 匹配中括号之外
SELECT cpu FROM laptop
WHERE cpu REGEXP '[^i57]'

# 指定范围
SELECT id FROM laptop
WHERE id REGEXP '[0-9]'

# 拼接和别名
SELECT CONCAT(id,'(',cpu,')') AS cpulist FROM laptop

# 文本处理函数

# left返回数据从左边开始几个字符，超了也不报错
SELECT LEFT(cpu, 1) FROM laptop
SELECT RIGHT(cpu, 10) FROM laptop

# 长度返回内容的字符个数
SELECT LENGTH(id) FROM laptop

# 返回子串的起始位置，找不到就是0
SELECT LOCATE("a", cpu) FROM laptop

# 从第几个位置开始，包括这一位（这里是2）找子串
SELECT LOCATE(1, id, 2) FROM laptop 

# 从第二位开始返回后面的字符（包括这一位） 
SELECT SUBSTRING(`disk`, 2) FROM laptop
SELECT SUBSTRING(`disk` FROM 2) FROM laptop

# 从第二位开始返回2个字符
SELECT SUBSTRING(`disk`, 2, 2) FROM laptop
SELECT SUBSTRING(`disk` FROM 2 FOR 2) FROM laptop

# 找发音相似的
SELECT cpu FROM laptop
WHERE SOUNDEX(cpu)=SOUNDEX("raisen")

# lower upper大小写，不试了，trim rtrim ltrim 去空格，不试了

# 分组和聚集
SELECT cpu, COUNT(id) FROM laptop
GROUP BY cpu
HAVING cpu <> "rayzen"

# 子查询
SELECT cpu FROM laptop
WHERE `memory`=16 AND graphics NOT IN (SELECT graphics FROM laptop WHERE graphics="uhd")

# 连结
SELECT l1.cpu 
FROM laptop AS l1, laptop AS l2
WHERE l1.id=l2.id AND l1.memory=16 AND l1.graphics="vega"

# 组合
SELECT id FROM laptop
WHERE id<11
UNION
SELECT id FROM laptop
WHERE id>20