SQLite 备忘录013

表达式

表达式是一个或多个值、运算符和计算值的SQL函数的组合。

-- 数据准备
sqlite> .headers on
sqlite> .mode column
sqlite> select * from COMPANY ;
ID          NAME        AGE         ADDRESS     SALARY
----------  ----------  ----------  ----------  ----------
1           Paul        32          California  20000.0
2           Allen       25          Texas       15000.0
3           Teddy       23          Norway      20000.0
4           Mark        25          Rich-Mond   65000.0
5           David       27          Texas       85000.0
6           Kim         22          South-Hall  45000.0
7           James       24          Houston     10000.0

布尔表达式

在匹配单个值的基础上获取数据。

SELECT column1, column2, columnN 
FROM table_name 
WHERE SINGLE VALUE MATCHING EXPRESSION;

sqlite> SELECT * FROM COMPANY WHERE SALARY = 10000;
ID          NAME        AGE         ADDRESS     SALARY
----------  ----------  ----------  ----------  ----------
7           James       24          Houston     10000.0

数值表达式

SELECT numerical_expression as  OPERATION_NAME
[FROM table_name WHERE CONDITION] ;

sqlite> .mode line
sqlite> SELECT (15 + 6) AS ADDITION;
ADDITION = 21
sqlite>
sqlite> SELECT COUNT(*) AS "RECORDS" FROM COMPANY;
RECORDS = 7

日期表达式

返回当前系统日期和时间值

sqlite> SELECT CURRENT_TIMESTAMP;
CURRENT_TIMESTAMP = 2023-04-21 06:45:00