[FEATURE]Add ispresent PPL command

[YANG-DB]

Is your feature request related to a problem?
Add ispresent command for PPL spark based execution driver .

Since spark sql doesnt offer such expression a possible option would be:

• use WHERE spark sql command

    WHERE  "column_name" IS NOT NULL

• register a custom expression ispresent

Do you have any additional context?

• [META]Add Missing PPL commands - campaign #408

[lukasz-soszynski-eliatra]

I created a working PoC (proof of concept). The source code can be found eliatra#3.

The usage of the commands looks as follows.

search source=people | is_present name;
search source=people | is_present age;
search source=people |  is_present age, name;

Please let me know if such an approach meets your expectations.

BTW, the MR is not yet ready. Documentation and tests need to be created.

[salyh]

We need a final decision wether this should be a command or a function like asked in #512 (comment)

[lukasz-soszynski-eliatra]

ispresent implemented as a function. @YANG-DB the MR is ready for review.

Example: search source=people | eval p=ispresent(age) | where ispresent(age);