mysql：检查一个查询中是否存在表和列？

Question

Working with multiple tables, the task is to check if the table exists and its certain columns exist, too.

The query

SELECT
    (TABLE_NAME) AS table_name,
    (GROUP_CONCAT(COLUMN_NAME)) AS column_name
FROM information_schema.COLUMNS
WHERE
    TABLE_SCHEMA = 'dbms'
AND
    TABLE_NAME IN ('user', 'status')
AND
    COLUMN_NAME IN ('id', 'name')
GROUP BY table_name

works fine to detect existing columns, but returns nothing if either table does not exist or none of the columns exist. The latter should be differentiated. How to? How to know whether it's a table or column names that do not exist?

To clarify, the query above will return 2 rows by 2 columns:

user   | id, name
status | id, name

means, each table has both of the columns.

Changing one column name to, say, name1, will result in:

user   | id
status | id

means, only id exists.

Changing column names to name1, id1 will return nothing. This is the problem. It is impossible to say whether tables do not exist or columns.

It would be good if the return would look something like:

user   | ''
status | ''

and if, say status does not exist, then like:

user   | ''

what can be decoded as only user table exists, and none of the columns named in it.

Answer 1

You cannot use WHERE for column_name is you still want rows in the result set even if they don't match. It looks like the only real WHERE clause you want is based on the table name, and the column name is simply a display condition.

SELECT
    table_name
    GROUP_CONCAT(IF(column_name IN ('id','name'), column_name, NULL))
FROM information_schema.columns
WHERE table_schema = 'dbms'
AND table_name IN ('user','status')
GROUP BY table_name

Answer 2

you just need to change your logic in and condition as mentioned in your query TABLE_SCHEMA = 'dbms' AND TABLE_NAME IN ('user', 'status') AND COLUMN_NAME IN ('id', 'name')

it will fetch only the resultset if there are tables users or status with column name id or name in dbms, what you can do is separately check for tables and if table exist check for columns. I hope it would help