Sqlite 简明教程
SQLite - Expressions
表达式是值、操作符和 SQL 函数的一个或多个组合，它们的值计算为一个值。
An expression is a combination of one or more values, operators, and SQL functions that evaluate to a value.
SQL 表达式类似于公式，它们以查询语言书写。您还可以用它来查询特定的数据集的数据库。
SQL expressions are like formulas and they are written in query language. You can also use to query the database for a specific set of data.
Syntax
考虑以下 SELECT 语句的基本语法：
Consider the basic syntax of the SELECT statement as follows −
SELECT column1, column2, columnN
FROM table_name
WHERE [CONDITION | EXPRESSION];以下列出了 SQLite 表达式的不同类型。
Following are the different types of SQLite expressions.
SQLite - Boolean Expressions
SQLite 布尔表达式根据匹配的单个值获取数据。以下为语法：
SQLite Boolean Expressions fetch the data on the basis of matching single value. Following is the syntax −
SELECT column1, column2, columnN
FROM table_name
WHERE SINGLE VALUE MATCHTING EXPRESSION;考虑具有以下记录的 COMPANY 表 -
Consider COMPANY table with the following records −
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以下是显示 SQLite 布尔表达式用法的简单示例：
Following is a simple examples showing the usage of SQLite Boolean Expressions −
sqlite> SELECT * FROM COMPANY WHERE SALARY = 10000;
ID NAME AGE ADDRESS SALARY
---------- ---------- ---------- ---------- ----------
4 James 24 Houston 10000.0SQLite - Numeric Expression
这些表达式用于在任何查询中执行任何数学运算。以下为语法：
These expressions are used to perform any mathematical operation in any query. Following is the syntax −
SELECT numerical_expression as OPERATION_NAME
[FROM table_name WHERE CONDITION] ;这里，numerical_expression 用于数学表达式或任何公式。以下是显示 SQLite 数值表达式用法的简单示例。
Here, numerical_expression is used for mathematical expression or any formula. Following is a simple example showing the usage of SQLite Numeric Expressions.
sqlite> SELECT (15 + 6) AS ADDITION
ADDITION = 21有几个内置函数，如 avg(), sum(), count(), 等，以执行所谓的 aggregate data calculations 操作（针对一张表或一个特定的表列）。
There are several built-in functions such as avg(), sum(), count(), etc., to perform what is known as aggregate data calculations against a table or a specific table column.
sqlite> SELECT COUNT(*) AS "RECORDS" FROM COMPANY;
RECORDS = 7