| 关系代数运算符 |
对应sql语句 |
| 聚合操作 |
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| ∪ (UNION)并 |
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| ∩ (INTERSECTION)交 |
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| - (DIFFERENCE)差 |
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| × (Cartesian PRODUCT)笛卡尔积 |
from |
| 纯关系操作 |
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| π (PROJECT)投影 |
select |
| σ (SELECT)选择 |
where |
| ⋈ (JOIN)链接 |
JOIN(mysql> SELECT a.age, b.author FROM books a INNER JOIN books2 b ON a.age>25;) |
| ÷ (DIVISION)除 |
exists 和not exists(select * from books A where not exists(select age from books8 B WHERE A.age=B.age);) |
| |
|
| > 大于 |
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| >=大于等于 |
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| < 小于 |
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| <=小于等于 |
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| = 等于 |
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| !=不等于 |
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| ∧ 与 |
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| ∨ 或 |
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| ¬ 非 |
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| between 在两个值范围内查找 |
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| like 按通配符查找 |
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| regexp 按正则表达式查找 |
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组合条件 and, or
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select * from table_name where coll = xxx and col2 = xx or col3 > x; |