| 关系代数运算符 |
对应sql语句 |
| 聚合操作 |
|
| ∪ (UNION)并
|
|
|
∩ (INTERSECTION)交
|
|
| - (DIFFERENCE)差 |
|
| × (Cartesian PRODUCT)笛卡尔积
|
from |
| 纯关系操作 |
|
| 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 |
|
| >=大于等于 |
|
| < 小于 |
|
| <=小于等于 |
|
| = 等于
|
|
| !=不等于 |
|
| ∧ 与 |
|
| ∨ 或 |
|
| ¬ 非 |
|
| between 在两个值范围内查找 |
|
| like 按通配符查找 |
|
| regexp 按正则表达式查找 |
|
组合条件 and, or
|
select * from table_name where coll = xxx and col2 = xx or col3 > x; |