Query to select employed in a second job

Question

My table Has EmployeeId, JobId, StartDate and EndDate.
There are three possible employment statuses:
1. Employed in their first job, therefore EndDate is NULL
2. No longer employed so their EndDate IS NOT NULL
3. Employed in a second or subsequent job.  Therefore, one or more records with the EndDate NOT NULL and one record with the EndDate NULL.
How do I select out only those employees that are no longer employed but select all those that have a current job, even if they had a previous job?
Your help would be much appreciated.
Thanking you in anticipation.
Roger
rogerwithnell

Answer 1

>> My table Has EmployeeId, JobId, StartDate and job_end_date. <<
Please follow basic Netiquette and post the DDL we need to answer this. Follow industry and ANSI/ISO standards in your data. You should follow ISO-11179 rules for naming data elements. You should follow ISO-8601 rules for displaying temporal data. We need to
know the data types, keys and constraints on the table. Avoid dialect in favor of ANSI/ISO Standard SQL. 
And you need to read and download the PDF for: 
https://www.simple-talk.com/books/sql-books/119-sql-code-smells/
Since you are rude, we have to guess at everything. Why did you fail to post DDL, sample data, etc?  You seem to want the typical history table idiom: 
CREATE TABLE 
  REFERENCES Personnel(emp_id),
 job_id CHAR(12) NOT NULL
  REFERENCES Jobs(job_id),
 job_start_date DATE DEFAULT CURRENT_TIMESTAMP NOT NULL,
 job_end_date DATE,
 CHECK(job_start_date <=  job_end_date),
 PRIMARY KEY (emp_id,  job_start_date)
>> There are three possible employment statuses: <<
This is a standard SQL idiom. If you Google, you will find more constraints you need to add  to the table. But since you did not follow forum rules, I feel no obligation to cut & paste it. 
Do we have several job histories per employee? Can someone have overlapping jobs? How do we account for gaps in employment? If your boss is making you code from specification like this, quit. 
>> How do I select out only those employees that are no longer employed … <<
SELECT emp_id AS former_emp_id
  FROM Employment_History 
GROUP BY emp_id
 HAVING COUNT(*) = COUNT(job_end_date) ;
>> but select all those that have a current job, even if they had a previous job? <<
SELECT DISTINCT emp_id AS current_emp_id
  FROM Employment_History 
 WHERE  job_end_date IS NULL;
Study these and see why they work. Thinks sets and set-level atrtributes. 
--CELKO-- Books in Celko Series for Morgan-Kaufmann Publishing: Analytics and OLAP in SQL / Data and Databases: Concepts in Practice Data / Measurements and Standards in SQL SQL for Smarties / SQL Programming Style / SQL Puzzles and Answers / Thinking
in Sets / Trees and Hierarchies in SQL