| a、条件
????select?*?from?表?where?id > 1?and?name?!=?'alex'?and?num = 12;
????select?*?from?表?where?id?between?5?and?16;
????select?*?from?表?where?id?in?(11,22,33)
????select?*?from?表?where?id?not?in?(11,22,33)
????select?*?from?表?where?id?in?(select?nid?from?表)
b、通配符
????select?*?from?表?where?name?like?'ale%'??- ale开头的所有（多个字符串）
????select?*?from?表?where?name?like?'ale_'??- ale开头的所有（一个字符）
c、限制
????select?*?from?表 limit 5;??????????? - 前5行
????select?*?from?表 limit 4,5;????????? - 从第4行开始的5行
????select?*?from?表 limit 5 offset 4??? - 从第4行开始的5行
d、排序
????select?*?from?表?order?by?列?asc??????????????- 根据 “列” 从小到大排列
????select?*?from?表?order?by?列?desc?????????????- 根据 “列” 从大到小排列
????select?*?from?表?order?by?列1?desc,列2?asc????- 根据 “列1” 从大到小排列，如果相同则按列2从小到大排序
e、分组
????select?num?from?表?group?by?num
????select?num,nid?from?表?group?by?num,nid
????select?num,nid?from?表??where?nid > 10?group?by?num,nid?order?nid?desc
????select?num,nid,count(*),sum(score),max(score),min(score)?from?表?group?by?num,nid
????select?num?from?表?group?by?num?having?max(id) > 10
????特别的：group?by?必须在where之后，order?by之前
f、连表
????无对应关系则不显示
????select?A.num, A.name, B.name
????from?A,B
????Where?A.nid = B.nid
????无对应关系则不显示
????select?A.num, A.name, B.name
????from?A?inner?join?B
????on?A.nid = B.nid
????A表所有显示，如果B中无对应关系，则值为null
????select?A.num, A.name, B.name
????from?A?left?join?B
????on?A.nid = B.nid
????B表所有显示，如果B中无对应关系，则值为null
????select?A.num, A.name, B.name
????from?A?right?join?B
????on?A.nid = B.nid
g、组合
????组合，自动处理重合
????select?nickname
????from?A
????union
????select?name
????from?B
????组合，不处理重合
????select?nickname
????from?A
????union?all
????select?name
????from?B
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