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查询过滤重复
SELECT DISTINCT LoginPWD FROM student
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查询不为空的数据
SELECT sname FROM student WHERE sname IS NOT NULL;
SELECT sname FROM student WHERE sname IS NULL;
SELECT sname FROM student WHERE sname = '';
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模糊查询
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%全部匹配
_单个字符匹配
SELECT * FROM student WHERE sname LIKE '张%';
SELECT * FROM student WHERE sname LIKE '张__';
SELECT * FROM student WHERE sname LIKE '张_';
范围内查找
SELECT * FROM student WHERE sage IN (11,19);
between 根据一个范围值来查询
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in
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