I want to disable database prefix name while executing queries in MySQL.
I am using MySQl Workbench 6.3 CE.
For Example : SELECT * FROM test_db.test_table;
I want to remove test_db prefix.
If you're using MySQL workbench, in the lefthand pane, there is a list of available databases. If you're only using one, you can right click on it and select "set as default schema", then any queries you run in that MySQL session will no longer need to be prefixed with the DB name. However, if you want to query another DB in the same session, you will have to append that DB's name as a prefix, or do the same process, and set that DB as the default schema.
See this link for pretty pictures and a full description: https://www.quackit.com/mysql/tutorial/mysql_default_database.cfm
You have to tell it what database to use .. So you do it the way you are describing. .. Or you tell MySQL which database to use BEFORE the SELECT IE
use test_db;
SELECT * FROM test_table;
They way MySQL works is that you either explicitly state which schema a specific DB object is in (e.g. a table) or it uses the current default schema. If you don't have a default schema set and don't use fully qualfied names, you will get an error from MySQL saying that you have to define a default schema first.
So what you want to accomplish is impossible. Either set a default schema (it's a per connection setting, so you can set it once and use with your other queries as long as you keep the connection open) or fully qualify your DB objects (which is the most flexible approach and also avoids certain ambiquities, like same named tables in different schemas).
Related
Im trying to run this query to mask the contents in the column "audio" but keep getting the error message for wrong syntax
ALTER TABLE test
ALTER COLUMN audio varchar(10) MASKED WITH (FUNCTION = 'default()');
Where am i going wrong here. Pls help
MySQL does not support MASKED WITH syntax for Dynamic Data Masking. That's a proprietary feature of Microsoft SQL Server.
Microsoft SQL Server is a different RDBMS product from MySQL. Both of these products have features and syntax not supported by the other.
In MySQL 5.7, the DEFAULT can be a constant scalar value, or NULL, or CURRENT_TIMESTAMP. Those are the only options (see https://dev.mysql.com/doc/refman/5.7/en/data-type-defaults.html).
In MySQL 8.0, you can now use a constant expression for the default of a column (see https://dev.mysql.com/doc/refman/8.0/en/data-type-defaults.html).
In both versions, you must use the DEFAULT keyword.
Re your comment:
is there any other way, I can hide this column data for other users other than the root user
You can define a VIEW that excludes columns you want to hide. The view can read the base table, but it does not select the audio column. Users can read the view, but do not grant access to the base table to all users.
MySQL supports granting column-level privileges, but I have never seen anyone use them, and I don't know if they really work.
When I create a view, I create it in the context of the default database. So none of my references to table have a prefix which explicitly specify a database. However, when I edit a view in Workbench it automatically adds the database prefix!
I don't want the database prefix because when I restore a database under a different name it causes the restore to fail.
Is this possible to stop the prefixing in a view edit or there another way to get round the restore issue?
see https://bugs.mysql.com/bug.php?id=85176
The mysql 8.0.3 or above has been fixed
That's not possible. Views are stored in specific databases, not in some space "above" all databases. Consider following...
use playground_a; /*or whatever database*/
create view view_whatever as
select * from table_whatever;
use playground_b;
select * from view_whatever; /*here you will get an error that view_whatever does not exist*/
select * from playground_a.view_whatever; /*this works*/
That's why there will always be database prefixes in the view definition.
The only possibility I see, would be to use a stored procedure with a database name as parameter. In the procedure you'd use a prepared statement to execute a concated string of your query and the database name parameter. Of course this comes with downsides, like i.e. you can't add a where clause easily.
Creating the view without explicitely specifying a schema is a convenience feature. Behind the scenes the view is still saved in a specific schema (the default one in this case). When editing the source code is retrieved from the server which returns the real code (including the schema qualification). Hence already when you send the view code the association happens and cannot be removed again later.
Here is the command I use to create the backup:
mysqldump -u xxxxxx -pxxxxxx --routines database_a | gzip -9 > $FULLGZIPPATH
If you aren't easily able to update to MySQL 8.X then a workaround I've implemented was a post-processing step performed on the dump file itself prior to importing. I just remove the explicit prefixed db name, since the import process / view creation doesn't need it.
PowerShell -Command ^
"filter replace-dbname { $_ -replace '`<DB_NAME>`.`', '`' }"^
"Get-Content dump.sql -ReadCount 10 | replace-dbname | Add-Content replaced_dump.sql"
I've used PowerShell since I'm on Windows, but any scripting language will do. The only notes are that:
You'll need to do the replacement a-few-lines-at-a-time if you can't afford to read the entire dump into memory. Our dumps are about 11GB, which'd be a strain on our testing server's resources.
In my script I'm not doing an in-place string replacement, so it'll create a new dump file replaced_dump.sql alongside the original dump.sql. For me this was useful for diagnostics, because it meant if there was an issue, I didn't have to dump it again. Again, depending on your dump/disk size this might be an issue.
If your database happens to have `<DB_NAME>`.` as content in something like a text-field, this basic approach will also remove the string there as well.
How do I stop using a database?
To start mysql, you can use:
mysql -u root -pXXXX<ENTER>
At this time, no database is selected. We'll call this
state 1
To select (or use) a database:
use "MyDB";
.....My operations or queries
Now, I want to return to state 1 (without any database selected). How I can do that? I can select another database, but I don't want to do that.
What you are asking for is not possible. The only way to return to that state is to disconnect and then reconnect.
If you are just looking to switch away from your current db, you can switch to a system database, such as the internal "mysql" database:
use mysql
Or you could create an empty database and use that:
create database empty;
use empty
Try prompt.
From the MySQL manual:
Reconfigure the mysql prompt to the given string. The special
character sequences that can be used in the prompt are described later
in this section.
If you specify the prompt command with no argument, mysql resets the prompt to the default of mysql>.
Ike Walker's answer is on the right track me thinks.
Create a swap space, or you could just halt the server (stop the process) and restart it I suppose. That defeats the purpose of the server—but it would for sure wind up where you want it with no database in 'use'.
I'm certain you know this, but I mention here just in case. You never know. Someone might not know it is possible to do this.
We will migrate the database from mysql to postgresql in our product(through java). So we need to change the mysql query to postgresql query in java application. How to create the table i.e., databasename.tablename in postgresql.
For mysql, we can directly create the table e.g create table information.employee.
Here database name is "information" and table name is "employee" . Is it possible to achieve same query in postgresql.
I searched google it says cross database reference is not possible. Please help me.
I saw pg_class table it contains the table names in the specific database, like wise databse and tables relationships are stored in any other table.
This is normally done using schemas rather than databases, which is more or less like how MySQL organizes it anyway.
Instead of
create database xyz
use
create schema xyz
When you create tables, create them:
create table xyz.myTable
you will need to update your search path to see them on the psql command line tool, or if you want to query them without using the schema explicitly. The default schema is public, so when you create a table without a schema name, it ends up in public. If you modify your search_path as below, the default schema becomes the first in the list: xyz.
set search_path=xyz,public,pg_catalog;
and you must not have spaces in that statement. You can do it globally for a user/role too:
alter role webuser set search_path=xyz,public,pg_catalog;
Also, don't forget that postgresql string matches are case sensitive by default (this one catches people out a lot).
If you want to have different physical locations for the files for each schema, you can do that with tablespaces. If you have a look at the postgresql documentation page, they have info on how to do it, it's pretty easy.
database in MySQL == schema in PostgreSQL. So you will most probably want to migrate all your mysql dbs into one postgres db. Then you will be able to do "cross-database" queries.
See my answer to this question: Relationship between catalog, schema, user, and database instance
I would like to select data from a second MySQL database in order to migrate data from one server to another.
I'm looking for syntax like
SELECT * FROM username:password#serverip.databaseName.tableName
Is this possible? I would be able to do this in Microsoft SQL Server using linked servers, so I'm assuming it's possible in MySQL as well.
You can create a table using FEDERATED storage engine:
CREATE TABLE tableName (id INT NOT NULL, …)
ENGINE=FEDERATED
CONNECTION='mysql://username:password#serverip/databaseName/tableName'
SELECT *
FROM tableName
Basically, it will serve as a view over the remote tableName.
There are generally two approaches you can take, although neither of them sound like what you're after:
Use replication and set up a master/slave relationship between the two databases.
Simply dump the data (using the command line mysqldump tool) from the 1st database and import it into the 2nd.
However, both of these will ultimately migrate all of the data (i.e.: not a subset), although you can specify specific table(s) via mysqldump. Additionally, if you use the mysqldump approach and you're not using InnoDB you'll need to ensure that the source database isn't in use (i.e.: has integrity) when the dump is created.
You can't do this directly, but as someone else alluded to in a comment, you can use mysqldump to export the contents of a table as a SQL script.
At that point you could run the script on the new server to create the table, or if more manipulation of the data is required, import that data into a table with a different name on the new server, then write a query to copy the data from there.