pig 的chararry类型可以是由场，通过现场实地比较。
element_id 这是chararray种类。
声明：
no_app_category_mapping = filter no_element_id by element_id == '' or element_id is null or element_id == '0' or element_id >='14';
当中，element_id >='14'是错误的使用方法。
comparison operator不能操作chararray类型。
运行结果是 element_id为8 的被找出来了。‘8’>='14'。非常奇怪啊！
而改成 element_id <='14'时。再运行时。
运行结果找到了element_id =‘1’和element_id =‘11’的，说明不行。
原理：预计是升级为bytearray，然后，按字段比較，逐个字段，所以，8>1。而1同样时。1<4
所以11小于14。而8大于14.
pig官网有说明：貌似仅仅能用==和！=。两边不一致是。implicit cast支持从低到高，不支持高到低。
例如以下：
Comparison Operators
Description
| Operator | Symbol | Notes |
| equal | == | |
| not equal | != | |
| less than | < | |
| greater than | > | |
| less than or equal to | <= | |
| greater than or equal to | >= | |
| pattern matching | matches | Takes an expression on the left and a string constant on the right. expression matches string-constant Use the Java for regular expressions. |
Use the comparison operators with numeric and string data.
Examples
Numeric Example
X = FILTER A BY (f1 == 8);
String Example
X = FILTER A BY (f2 == 'apache');
Matches Example
X = FILTER A BY (f1 matches '.*apache.*');
Types Table: equal (==) operator
| bag | tuple | map | int | long | float | double | chararray | bytearray | boolean | datetime | biginteger | bigdecimal | |
| bag | error | error | error | error | error | error | error | error | error | error | error | error | error |
| tuple | boolean (see Note 1) | error | error | error | error | error | error | error | error | error | error | error | |
| map | boolean (see Note 2) | error | error | error | error | error | error | error | error | error | error | ||
| int | boolean | boolean | boolean | boolean | error | cast as boolean | error | error | error | error | |||
| long | boolean | boolean | boolean | error | cast as boolean | error | error | error | error | ||||
| float | boolean | boolean | error | cast as boolean | error | error | error | error | |||||
| double | boolean | error | cast as boolean | error | error | error | error | ||||||
| chararray | boolean | cast as boolean | error | error | error | error | |||||||
| bytearray | boolean | error | error | error | error | ||||||||
| boolean | boolean | error | error | error | |||||||||
| datetime | boolean | error | error | ||||||||||
| biginteger | boolean | error | |||||||||||
| bigdecimal | boolean |
Note 1: boolean (Tuple A is equal to tuple B if they have the same size s, and for all 0 <= i < s A[i] == B[i])
Note 2: boolean (Map A is equal to map B if A and B have the same number of entries, and for every key k1 in A with a value of v1, there is a key k2 in B with a value of v2, such that k1 == k2 and v1 == v2)
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