hive在表关联时尽量避免隐式转化，可以使用cast强转，下面例子中tableA表的order_no是bigint类型，tableB的order_no是string类型
select
a.order_no,
c.order_no as c_order_no,
a.order_no=c.order_no
from tableA a
left join tableB b
on a.order_no=b.order_no
left join
(select
t1.order_no
from tableA t1
join tableB t2
on t1.order_no=t2.order_no
) c
on a.order_no=c.order_no
where a.order_no=81268102217186906;

±-------------------±-------------------±-------+
| a.order_no | c_order_no | _c5 |
±-------------------±-------------------±-------+
| 81268102217186906 | 81268102217186920 | false |
| 81268102217186906 | 81268102217186906 | true |
±-------------------±-------------------±-------+
出现错误

可以转换的数据类型有，以及强制转换方法：
强制转换就是用js的方法转换

1. Number
   1. Number()
   2. Number().parseInt()
   3. Number().paseFloat()
2. String
   1. String()
   2. toString()
3. Boolean
   1. Boolean()

Number

//强制转换
//1.Number
let a = '123'
let a_num = Number(a)
console.log(a_num);			//123

//int
let b = '123.31'
let b_num = Number.parseInt(b)
console.log(b_num)			//123

//float
let b = '123.31'
let b_num = Number.parseFloat(b)
console.log(b_num)			//123.31

//隐式转换
//乘
let aa = '123'
let aa_num = aa*0
console.log(aa_num) //123
//除
let bb = '123'
let bb_num = bb/0
console.log(bb_num) //123
//加
let cc = '123'
let cc_num = cc+0;
console.log(cc_num) //1230
//加号 在js中和字符串相加有拼接字符串的作用

String

//强制转换
//String
let a = 123;
let a_str = String(a)
console.log(a_str)			//'123'
//toString
let b = 123;
let b_str = b.toString()
console.log(b_str)			//'123'

//隐式专函
let c = 123;
let c_str = c+''
console.log(c_str)			//'123'

Boolean

//强转换
let a = 1123;
console.log(Boolean(a))		//true

let b = ''
console.log(Boolean(b))		//false

let c = 0;
console.log(Boolean(c))		//false
//undefined,数值0,空字符串,null转换都为false

//隐式转换
let d = 123;
let d_boolean = !!d
console.log(d_boolean)		//true

let const 和 var 的区别

1. let：拥有块级作用域，变量不可以提升，可以修改，不可重复声名
2. const：块级作用域，不可变量提升，不可以修改，不可重复声名
3. var：函数作用域，变量可以提升，可以修改，可以重复声名

let

//重复申明
let a = 13;
let a = 1123123;
//报错：Uncaught SyntaxError: Identifier 'a' has already been declared

//先使用，在声名，变量提升
console.log(b)
let b = 123;
//报错:demo.html:58 Uncaught ReferenceError: Cannot access 'd' before initialization at

//修改 不加修饰符(var,let,const)
let c = 24;
c = 30;
console.log(c)			//30

//块级作用域
//父类中的名字，子类中如果有那么就相当于 重写
//兄弟块，遵守上面的，且兄弟之间不会互相影响
{
	let k_a = 'father'
	{		//son1
		let k_a = 'son'
		let k_b = 'son1'
	}
	{		//son2
		let k_b = 'son2'
	}
}

var

//可以变量提升
console.log(a)		//不会报错，打印undefined
var a = 123;

//重复声名，覆盖老的
var b = 123;
var b = 321;
console.log(b)		//321

//函数作用域
function d(){
	var c = 'dd'
	console.log(c)	//'dd'
	//函数作用域，只有在函数内可以使用
}
d();
console.log(c)   //会报错 c is not defined

const

console.log(a) //报错
const a = 123;

const b = 321;
b = 123;
console.log(b)	//报错

let c1 = 11;
let c1 = 22;
console.log(c1)