别名与算术

SQL 中级

Jasmin Ludolf

Data Science Content Developer, DataCamp

算术

+、-、*、/

SELECT (4 + 3);

|7|

SELECT (4 * 3);

|12|

SELECT (4 - 3);

|1|

SELECT (4 / 3);

|1|

SELECT (4 / 3);

|1|

SELECT (4.0 / 3.0);

|1.333...|

聚合函数一个数据表的示例，红框圈出单列，在 SQL 中也称为字段。

算术一个数据表的示例，红框圈出单条记录，也称为行。

SELECT (gross - budget)
FROM films;

|?column?|
|--------|
|null    |
|2900000 |
|null    |
...

SELECT (gross - budget) AS profit
FROM films;

|profit  |
|--------|
|null    |
|2900000 |
|null    |
...

SELECT MAX(budget), MAX(duration)
FROM films;

|max        |max|
|-----------|---|
|12215500000|334|

SELECT MAX(budget) AS max_budget,
       MAX(duration) AS max_duration
FROM films;

|max_budget |max_duration|
|-----------|------------|
|12215500000|334         |

SELECT budget AS max_budget
FROM films
WHERE max_budget IS NOT NULL;

column "max_budget" does not exist
LINE 5: WHERE max_budget IS NOT NULL;
              ^

SQL 中级