I'm surprised I didn't find this answer out there.
I know very well what the difference between a table and a view is. BUT..how do I DETERMINE whether a db object is a table or view? Since
show tables;
will show both tables and views - and there is no "show views" command.
to determine in my coding (which has to read multiple objects and may not "know" better), I do this:
show create view my_table_or_view
and if I get an error, which I prevent from dying, it's a table. Pretty clumsy, is there a better way?
try this variation instead ...
show full tables;
the Table_type column will give the info you require :)
You can use the following query and if it returns a record it's a table
SELECT *
FROM information_schema.tables
WHERE 'TABLE_TYPE' = 'BASE TABLE'
AND table_name = 'your table name'
Related
I have a database that contains a table per client, each table has the same columns in them. We're talking a few thousand client tables.
I need to add new columns to each of these tables for new development but cannot find a way to recurse all the tables in the database to add the columns. I know MS SQL has something sp_MSforeachtable which does maybe what I'm asking but I don't know if MySQL has anything similar?
As per this previous answer in SO you could do something like this :
select concat('ALTER TABLE `',table_name,'` ADD `test` INT NOT NULL AFTER `column_x`;')
from information_schema.tables
where table_schema = 'your_db_name'
Then remove the few tables not about client (here's hoping client is the only entity to have "private table") or if possible add a condition on the table_name (like AND table_name LIKE "client_%"), and execute the whole batch.
The 2nd solution, to use procedure, is too complex (for me) for this use case, but maybe someone more skilled than me in PLSQL won't agree.
For some unknown reason, the info of 'information_schema.tables' is not match to real tables:
First, find table-name from information_schema.tables, there is one result;
Then, select * from table-name, it shows table not exist! /(ćoć)/~~
I try to create a new table(MyISAM engine) with same name, it create OK!
Then, find table-name from information_schema.tables, there are two result!
And select * from table-name shows empty set, it's normally.
Until now, table can be use, but can not be drop completely.
If drop table, it return the "First".
As the following image:
all the step
I am searching for a long time on net. But no use. Please help or try to give some ideas how to achieve this......
The image shows nothing wrong to me. When you run this:
SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE
TABLE_NAME = 'report_instance_performance_20160614
and get a result, you are probably getting a result for a table of that name in a different schema from where you ran that query. It would be more helpful to run this to see if something were wrong:
SELECT TABLE_SCHEMA, TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE
TABLE_NAME = 'report_instance_performance_20160614'
My assertion that that table exists in another schema but not that one that you're running in the query from is that you're getting the doesn't exist error when you try and SELECT from it.
Next, when you create a new instance of that table and then run your INFORMATION_SCHEMA.TABLES query, you are getting two results because you've now created a table with that name in your current schema. If that table had existed in your current schema, you would've gotten an error that a table of that name already existed in the schema. This further supports my assertion that report_instance_performance_20160614 exists in a different schema.
Lastly, since the table is newly created and you haven't INSERTed anything into the table before SELECTing from it, it's totally normal that the table would be empty.
I have the following problem. I have Table A and would like to join to table B if table B exists. Can this be done? I am only writing SQL in WorkBench to try achieve it.
I am aware I cannot use the EXISTS option as I have tried typing it out but it prompts for an error.
Any suggestions would be greatly appreciated.
Thanks.
I managed to do this using EXECUTE, so using a query that is only prepared at runtime:
SET #sqlCommand = IF(
EXISTS (SELECT column_name FROM information_schema.columns WHERE table_schema = '{{yourschemaname}}' AND table_name = '{{yourtablename}}' AND column_name = '{{yourcolumnname}}'),
'SELECT \'Yes! Good to go!\' as ColumnExists',
'SELECT \'Nope!\' as ColumnExists');
PREPARE executable FROM #sqlCommand;
EXECUTE executable;
Note that the two selects at the center (Yes!/No!) are the custom statements that are to be executed conditionally. So if the column exists, the first command is executed (select 'yes!'), otherwise the second one (select 'nope').
I got the hint from this discussion here.. have a look if you're looking for the MSSQL equivalent: https://ask.sqlservercentral.com/questions/97579/check-if-table-exists-in-join.html
Data manipulation language statements are typically written for a specific schema; you are assumed to know what the schema looks like when you issue the statement. So you don't generally have the capacity to ask whether a particular schema object exists or has a particular structure. You could however write a stored procedure that did different things depending upon the schema. You have the ability in a stored procedure to use conditional statements and to look in INFORMATION_SCHEMA.
I have just noticed that where mysql_num_rows should return the number of rows returned for either SELECT or SHOW commands, returns 0 for SHOW TABLE command specifically.
Instead it shows the affected rows count instead of the num rows.
Can anyone please tell me if this is a bug or if am I missing anything here?
SHOW TABLE command is used to Show you table name in your database . On the other hand , mysql_num_rows is used to count how many result got from your query. This query is depend on your requirement basis ...
As stated on the PHP documentation page:
Retrieves the number of rows from a result set. This command is only
valid for statements like SELECT or SHOW that return an actual result
set.
My guess is that SHOW TABLES is not a technical query that would produce the type of result set that mysql_num_rows enumerates.
These "helper" functions (such as SHOW, EXPLAIN, DESCRIBE etc.) won't let you issue their results like you would in a regular table.
But if you're looking for how you can do this, for SHOW TABLES you can do
SELECT `table_name` FROM `information_schema`.`tables`
WHERE `table_schema`=DATABASE()
-- DATABASE() selects current database name
-- you can use the name of any database as a string instead
So basically you can use the information_schema database to get that information.
It was a bug in mysql, fixed it with the update.
Is it possible to know when a view has been created or updated?
If I run a query on information_schema.tables I get these infos only for "base table" while for view everything is equals to null. Thanks
No, it's not possible because view is not a table and not contain any physical data. MySQL creates view on the current data which exist in other tables, so you only can get update time for tables.
View is only a definition, and that definition are stored in INFORMATION_SHEMA. You can only get information about definition:
SELECT VIEW_DEFINITION FROM INFORMATION_SCHEMA.VIEWS
WHERE TABLE_SCHEMA = 'test' AND TABLE_NAME = 'v';
But, you can't get update or created time.