Do I need a while loop to insert based on conditions?

问题

I want to insert values in a column based on the following conditions. Name of the column to be inserted is project_renewal.

If decimal exists in project_code, insert the numbers after decimals.

SELECT substring_index(project_code, '.', -1)
FROM projects where
project_code like '%.%'

If no decimal, insert 0.

SELECT project_code
FROM projects where
project_code not like '%.%'

Order of insert must be the same as the order of reading values from project_code.

回答1:

 INSERT IGNORE INTO outtable (code)
 SELECT IF (project_code LIKE '%.%'
     , substring_index(project_code, '.', -1)
     , 0)
 FROM projects

回答2:

You can do it like this:

INSERT INTO tablename(project_renewal)
SELECT trim(trailing '0' from substring_index(project_code, '.', -1)) + 0
FROM projects

See the demo.

If you want to update a column in the same table then do it with an UPDATE statement:

UPDATE projects
SET project_renewal = trim(trailing '0' from substring_index(project_code, '.', -1)) + 0

See the demo.

来源：https://stackoverflow.com/questions/60083029/do-i-need-a-while-loop-to-insert-based-on-conditions