I want to alter multiple tables using regex,
ALTER tablename DROP INDEX feed
the following are the table names
wp_1_ai1ec_event_feeds
wp_12_ai1ec_event_feeds
wp_14_ai1ec_event_feeds
wp_19_ai1ec_event_feeds
and so on..
I tried using regex in place of tablename
alter wp_[0-9]+_ai1ec_event_feeds drop index feed
but I get syntax error. How to achieve this?
You can fetch the table names using SHOW TABLES, then do the ALTER queries for each of these tables.
To fetch the table names, you can use the simple LIKE matching:
SHOW TABLES LIKE 'wp\_%\_ai1ec\_event\_feeds';
This will work as long as there are no tables like wp_letters_ai1ec_event_feeds.
Related
I want to create a new table with rows of the column names. Essentially, I want to put the output of a decribe statement into a new table, so that I can use a where clause to only extract certain column names. I'm using sparksql.
How do I do this? Thanks.
No need to create an additional table just use either SHOW COLUMNS command instead of describe with filter, or query information_schema.columns table with a select.
I want to search the structure of my MySQL db and replace structures that contain or equal "xyz*"... column names and table names are the main thing, but I'd like to search all structures.
Then, I want to replace "xyz*" with "abcdefg".
I doubt one can do this with one query. What you can do is create ALTER statements. I would write a small program (in the language of your choice) and
first I would get the table names like this:
select table_name from information_schema.tables;
The result set has to be checked in a loop, if there is a table named "xyz*" then create an ALTER statement:
RENAME TABLE tbl_name TO new_tbl_name
For the colums, you would have to get each Table again, then all colums for each table:
SELECT COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'tbl_name';
the again a loop to change the columns name, this time using ALTER TABLE.
see also:
https://dev.mysql.com/doc/refman/5.1/en/alter-table.html
https://dev.mysql.com/doc/refman/5.0/en/rename-table.html
I can "copy" a table using:
CREATE TABLE copy LIKE original_table
and
CREATE TABLE copy as select * from original_table
In the latter case only the data are copied but not e.g primary keys etc.
So I was wondering when would I prefer using a select as?
These do different things. CREATE TABLE LIKE creates an empty table with the same structure as the original table.
CREATE TABLE AS SELECT inserts the data into the new table. The resulting table is not empty. In addition, CREATE TABLE AS SELECT is often used with more complicated queries, to generate temporary tables. There is no "original" table in this case. The results of the query are just captured as a table.
EDIT:
The "standard" way to do backup is to use . . . . backup at the database level. This backs up all objects in the database. Backing up multiple tables is important, for instance, to maintain relational integrity among the objects.
If you just want a real copy of a table, first do a create table like and then insert into. However, this can pose a challenge with auto_increment fields. You will probably want to drop the auto_increment property on the column so you can populate such columns.
The second form is often used when the new table is not an exact copy of the old table, but contains only selected columns or columns that result from a join.
"Create Table as Select..." are most likely used when you have complex select
e.g:
create table t2 as select * from t1 where x1=7 and y1 <>2 from t1;
Now, apparently you should use Create Like if you don't need such complex selects. You can change the PI in this syntax also.
Is it possible to use the LIKE statement on ALTER TABLE similar to CREATE TABLE in MySQL?
Eg. 'CREATE TABLE db.tbl1 LIKE db.tbl2'
This clones a database table's structure. I want to alter an existing table with the same columns but to pick up the primary keys of another table.
I was thinking of something like 'ALTER TABLE db.tbl1 LIKE db.tbl2' but this throws back an error.
Any ideas?
Thanks
I required a similar thing and settled to use the following procedure:
ALTER TABLE tbl1 RENAME tbl1_old;
CREATE TABLE tbl1 LIKE tbl2;
INSERT INTO tbl1 SELECT * FROM tbl1_old;
DROP TABLE tbl1_old;
Altough this is not a single statement it should do the job. Only problem could be different index settings (UNIQUE, etc.) which cause errors when doing the "INSERT INTO" of the original table contents.
Everything ALTER TABLE can do is explained here.
As you can see importing indexes from another table is not mentioned. You could probably do that with some clever information_schema querying, but I don't think it would be worth the cost.
It seems you can't.
I tried writing query using exists, but no success so far. Searching hasn't helped so far.
If you attempt to alter a table that does not exist, the query will fail with an error: Table 'database.table' doesn't exist
MySQL does support ALTER IGNORE TABLE, but that only turns errors into warnings if you're attempting to create a unique index while there are values in the table that violate that index.
If you would like to make sure that you do not produce any database queries, I would suggest ensuring the table's existence using SHOW TABLES LIKE 'tablename' before running your ALTER TABLE query.