hive - concat 函数

   concat 函数在连接字符串的时候，只要察团其中一个裂汪是NULL，那么将返回NULL

hive>select concat('a','b')

ab

hive>select concat('a','肆没仔b',null)

NULL

MYSQL里的CONCAT函数用于将两个字符串连接起来，形成一个单一的字符串。

如下面的例子：

mysql> select concat('11','22','33')

+------------------------+

| concat('11','22','33') |

+------------------------+

| 112233 |

+------------------------+

1 row in set (0.00 sec)

MySQL的concat函数在连接字符串的时候，只要其中一个是NULL,那么将返回NULL

mysql> select concat('11','22',null)

+------------------------+

| concat('11','22',null) |

+------------------------+

| NULL   |

+------------------------+

1 row in set (0.00 sec)

MySQL中concat_ws函数

使用方法：

contcat_ws(separator,str1,str2,...)

contcat_ws() 代表 CONCAT With Separator ，是CONCAT()的特殊形式。第一个参数是其它参数的分隔符。分隔符的位置放在要连接的两个字符串之间。分隔符可以是一个字符串，也可以是其它参数。老历

注意：

如果分隔符为 NULL，则结果为 NULL。函数会忽略任何分隔符参数后的 NULL 值侍档搜。

如连接后以逗号分隔

mysql> select concat_ws(',','11','22','33')

+-------------------------------+

| concat_ws(',','11','22','33') |

+-------------------------------+

| 11,22,33 |

+-------------------------------+

1 row in set (0.00 sec)

和MySQL中concat函数不同的是, concat_ws函数在执行的时候,不会因为NULL值而返回NULL 

mysql> select concat_ws(',','11','22',NULL)

+-------------------------------+

| concat_ws(',','11','22',NULL) |

+-------------------------------+

| 11,22 |

+-------------------------------+

1 row in set (0.00 sec)

HQL里的CONCAT函数大致用法更SQL的相同

我使用的常用形式为：

select a, b, concat_ws(',' , collect_set(cast(c as string)))

from table group by a,b

上文HQL中collect_set 有两个作用，第一个是 去重 ，去除group by后的重复元素，

第二个是形成一个 集合 ，将group by后属于同一组的第三列集合起来成为一个集合。与contact_ws

结合使用就是将这些元蠢扮素以逗号分隔形成字符串。当使用collect_list是则不会去重，它会将第三列的集合全部都列出来

cast  ，用法cast(value as type)，将某个列的值显示的转化为某个类型，cast(age as string ) 将int类型的数据转化为了String类型。

import javax.swing.*

import java.awt.*

import java.awt.event.*

public class Calculator extends JFrame implements ActionListener

{

private boolean dotExist, operated, equaled// 帮助运算的布尔笑肆变量

private double storedNumber// 目前的结果

private char lastOperator// 表示上一运算符

private JTextField operation// 结果栏

private JButton dot, plus, minus, multi, div, sqrt, equal, changePN, clear// 运算符

private JButton[] numbers// 数字

// 构造者

public Calculator()

{

setTitle("Calculator")

// 初始化变量

dotExist = false// 表示当前的数是否有小数点

operated = false// 表示任意运碰埋轿算符是否被按下

equaled = false// 表示等号是否被按下

storedNumber = 0

lastOperator = '?'液巧

// 初始化窗口变量

operation = new JTextField("0")

operation.setEditable(false)

numbers = new JButton[10]

for (int i = 0i <10i++)

numbers[i] = new JButton("" + i)

dot = new JButton(".")

plus = new JButton("+")

minus = new JButton("-")

multi = new JButton("*")

div = new JButton("/")

sqrt = new JButton("√")

equal = new JButton("=")

changePN = new JButton("±")

clear = new JButton("AC")

// 将窗口物体放入窗口

GridBagLayout layout = new GridBagLayout()

getContentPane().setLayout(layout)

addComponent(layout, operation, 0, 0, 4, 1)

addComponent(layout, numbers[1], 1, 0, 1, 1)

addComponent(layout, numbers[2], 1, 1, 1, 1)

addComponent(layout, numbers[3], 1, 2, 1, 1)

addComponent(layout, numbers[4], 2, 0, 1, 1)

addComponent(layout, numbers[5], 2, 1, 1, 1)

addComponent(layout, numbers[6], 2, 2, 1, 1)

addComponent(layout, numbers[7], 3, 0, 1, 1)

addComponent(layout, numbers[8], 3, 1, 1, 1)

addComponent(layout, numbers[9], 3, 2, 1, 1)

addComponent(layout, dot, 4, 0, 1, 1)

addComponent(layout, numbers[0], 4, 1, 1, 1)

addComponent(layout, sqrt, 4, 2, 1, 1)

addComponent(layout, plus, 1, 3, 1, 1)

addComponent(layout, minus, 2, 3, 1, 1)

addComponent(layout, multi, 3, 3, 1, 1)

addComponent(layout, div, 4, 3, 1, 1)

addComponent(layout, equal, 5, 0, 2, 1)

addComponent(layout, changePN, 5, 2, 1, 1)

addComponent(layout, clear, 5, 3, 1, 1)

}

// 对按钮进行反应的方法

public void actionPerformed(ActionEvent e)

{

JButton btn = (JButton)e.getSource()

if (btn == clear)

{

operation.setText("0")

dotExist = false

storedNumber = 0

lastOperator = '?'

}

else if (btn == equal)

{

operate('=')

equaled = true

}

else if (btn == plus)

{

operate('+')

equaled = false

}

else if (btn == minus)

{

operate('-')

equaled = false

}

else if (btn == multi)

{

operate('*')

equaled = false

}

else if (btn == div)

{

operate('/')

equaled = false

}

else if (btn == changePN)

{

operate('p')

operate('=')

equaled = true

}

else if (btn == sqrt)

{

operate('s')

operate('=')

equaled = true

}

else

{

if (equaled)

storedNumber = 0

for (int i = 0i <10i++)

if (btn == numbers[i])

{

if (operation.getText().equals("0"))

operation.setText("" + i)

else if(! operated)

operation.setText(operation.getText() + i)

else

{

operation.setText("" + i)

operated = false

}

}

if (btn == dot &&! dotExist)

{

operation.setText(operation.getText() + ".")

dotExist = true

}

}

}

// 进行运算的方法

private void operate(char operator)

{

double currentNumber = Double.valueOf(operation.getText()).doubleValue()

if (lastOperator == '?')

storedNumber = currentNumber

else if (lastOperator == '+')

storedNumber += currentNumber

else if (lastOperator == '-')

storedNumber -= currentNumber

else if (lastOperator == '*')

storedNumber *= currentNumber

else if (lastOperator == '/')

storedNumber /= currentNumber

else if (lastOperator == 'p')

storedNumber *= -1

else if (lastOperator == 's')

storedNumber = Math.sqrt(currentNumber)

else if (lastOperator == '=' &&equaled)

storedNumber = currentNumber

operation.setText("" + storedNumber)

operated = true

lastOperator = operator

}

// 快捷使用GridBagLayout的方法

private void addComponent(GridBagLayout layout, Component component, int row, int col, int width, int height)

{

GridBagConstraints constraints = new GridBagConstraints()

constraints.fill = GridBagConstraints.BOTH

constraints.insets = new Insets(10, 2, 10, 2)

constraints.weightx = 100

constraints.weighty = 100

constraints.gridx = col

constraints.gridy = row

constraints.gridwidth = width

constraints.gridheight = height

layout.setConstraints(component, constraints)

if (component instanceof JButton)

((JButton)component).addActionListener(this)

getContentPane().add(component)

}

// 主方法初始化并显示窗口

public static void main(String[] args)

{

Calculator calc = new Calculator()

calc.setSize(290, 400)

calc.setVisible(true)

}

}

如果你想加sin cos tan的话就建它们的按钮 在actionPerformed方法中的if-else语句中加else if (btn == sin){operate('S')operate('=')equaled = true}然后在operate方法加对应的语句就行了.记忆M+, M-没时间搞 这个应该比较简单容易明白吧.

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