SQL从所有列生成一个字符串

Question

I'm trying to create a separate log table, made from insert trigger values using now. The table has a lot of columns, so I was wondering if it is possible to convert all values of the row to one string.

Sample working code with two columns:

CREATE TRIGGER `TEST` AFTER INSERT ON `table` 
FOR EACH ROW BEGIN
    INSERT INTO change_log (string)
       VALUES (CONCAT("User: ", USER(), " Time: ", NOW(), " Insert: " , now.id, now.value));
    END

Answer 1

You can get a list of columns from the catalog. You can (group) concatenate them to form a concatenation expression.

SELECT concat('concat(',
              group_concat(concat('''',
                                  column_name,
                                  ': '', ',
                                  column_name)
                           SEPARATOR ', '),
              ')')
       FROM information_schema.columns
       WHERE table_schema = '<schema name>'
             AND table_name = '<table name>';

(Replace <schema name> and <table name> with your table's name and its schema.)

That will give you an expression like concat('a: ', a, 'b: ', b, 'c: ', c) (if the column name were a , b and c ).

Amend the result to include your meta data (user, time, etc.) and copy it into your trigger.

Or, if you want, you could also call the query from the catalog in your trigger. Amend it, so that in the trigger a string is built which holds the statement you want to execute and execute it with PREPARE ... EXECUTE ... DEALLOCATE PREPARE ... or EXECUTE IMMEDIATE ... (which is essentially shorthand for the former). More information on dynamic SQL in MariaDB can be found in "Prepared Statements " .

Answer 2

使用您的应用程序语言来构建JSON字符串-与您正在执行的操作非常相似，除了它还要处理嵌入式引号和反斜杠。