如果列名存储在变量中，如何获取列（NEW。{{col_name}}）-MySQL

Question

I have a variable:

DECLARE col_name CHAR(255);

How can I take column value from NEW/OLD if its name is stored in a variable.

NEW.{{col_name}}
OLD.{{col_name}}

I need to use this in the trigger.

MySql 5.5.40

Answer 1

if there is known scope of possible values (and i belive there is) one can use 'case'

SELECT
    CASE
    when @col_name = 'columnA' then NEW.columnA
    when @col_name = 'columnB' then NEW.columnB
    -- and so on..
    else 'unknown column'
    END AS [NEW_col_value],
    CASE
    when @col_name = 'columnA' then OLD.columnA
    when @col_name = 'columnB' then OLD.columnB
    -- and so on..
    else 'unknown column'
    END AS [OLD_col_value]
FROM
    ...

If type of column differs - then cast them to text..