Concatenating Fields连接字段

MySQL

  1. SELECT CONCAT(Code, ' - ', Name)
  2. FROM country

Ms SQL ,Access

SELECT Code + ' - ' + Name
FROM country

Oracle,PostgreSQL,SQLite,Firebird

SELECT Code || ' - ' || Name
FROM country

Remove Unwanted Spaces 删除不需要的空格

SELECT
RTRIM(Name),
LTRIM(Name),
TRIM(Name)
FROM country

Using Aliases 使用别名

SELECT TRIM(Continent) AS trim_continent
FROM country

--or

SELECT TRIM(Continent) trim_continent
FROM country

Mathematical Calculations 数学计算

SELECT
    Name,
    SurfaceArea, 
    Population,
    SurfaceArea / Population AS AreaPerPerson
FROM country
ORDER BY 4 DESC

CASE WHEN calause 条件函数

SELECT
Name,
Population, 
CASE WHEN Population > 1000000 THEN
     'Big city' ELSE
     'Small city' END CitySize
FROM world.city