The table names in my mysql database are dynamically generated. Is there some way to select data from tables which have a name matching a pattern? I guess it will look like:
select * from 'table_id_%'
No, you can't do that with MySQL. Tables in a query can't be dynamically specified - you have to build the list in your application (or do several single-table queries).
You can use INFORMATION_SCHEMA TABLES table to find tables you want, here is documentation: http://dev.mysql.com/doc/refman/5.0/en/tables-table.html . TABLES table has column NAME which represents names of tables. After finding table names you can run any sql queries you like.
That's not possible in the way you'd like to do it. However you could probably use prepared statements which are basically query-templates where you specificy the parameters (AFAIK also table names) that get replaced depending on your needs without copy and pasting the same query over and over again for different tables.
Related
I am not sure if this has been answered before but what I found i am not sure how to make work for me but here is my problem.
I have a database used to keep track of phones for multiple clients. What needs to be done is have a query that can be ran that will run against multiple databases on the same server. each database uses the same table name that I am looking at but the names are slightly different. I came up with this..
INSERT INTO `export db`.exportinfo2
SELECT *
FROM (SELECT * FROM `export db'.tentantnames).users
WHERE name = 'Caller ID:emergency' AND value > 0
What suppose to happen is from a table that has all the database names is is to got to each database and go into the table labeled users and run a where clause on the data then export results to a different database table
I know the code needs to be dynamic but I am not sure how to make it dynamic and function. The table that has all the names for the databases is automatically created every few days.. I am not sure what else needs to be said without sounding like i repeat myself but i just need help making a dynamic query that uses a table premade as database names and run a where statement on the same named table in each database which have their name stored in a different table.
You should look into Synonyms. It can be used to fulfill your purpose
Correct me if I'm wrong, but my understanding is that, in MSSQL, sub-structures of a database like Views, Schemas and Tables can be referenced using object notation such as:
Database.Schema.Table.Column
Each of these objects I believe has their own properties.
I need to replicate the structure of an MSSQL DB in MySQL and I am unsure what is the best practice.
I am thinking about creating tables in MySQL with the following naming convention:
Database
|---SubStructureX.Table
| |---Column_A
| |---Column_B
|---SubStructureY.Table
| |---Column_C
| |---Column_D
|
|
Therefore a MySQL query could look like this:
SELECT Column_A, Column_B FROM SubStructureX.Table
In short, "SubstructureX.Table" is just a table name that contains a dot. I would be doing this for ease of use during replication of the MSSQL structure. I don't care if the things before and after the dot are not objects in MySQL.
Is this good MySQL practice?
In MySQL? No, I would think that it's not good practice to use periods in table names at all. I would think that it's very bad practice. The dot is the reference operator in SQL. That means if you want to refer to a column using fully qualified notation, you do so like this:
SELECT Table.Column_A ...
Or, with backtick quoting:
SELECT `Table`.`Column_A` ...
Now, imagine if your table is named StructureX.Table. Just like with a space, you've got to quote that to escape it because you don't want MySQL to think the dot is an operator. That means your SQL has to look like this:
SELECT `StructureX.Table`.Column_A ...
Or, with backtick quoting:
SELECT `StructureX.Table`.`Column_A` ...
Doesn't that look like a syntax error to you? Like maybe it's supposed to be like this:
SELECT `StructureX`.`Table`.`Column_A` ...
This would be a nightmare to maintain and as a systems analyst I would hate any application or developer that inflicted this nomenclature on me. It makes me want to claw my eyes out.
Microsoft SQL Server is different because it supports multiple schemas within a single database, while MySQL treats schema as a synonym for database. In MS SQL Server, schemas are collections of objects, and you can use them to organize your tables, or apply security to tables as a group. The default schema is dbo, which is why you see that one listed so often. In MS SQL Server syntax, this:
SELECT [StructureX].[Table].[Column_A] ...
Means within the current database, the schema named StructureX, table named Table, and column name Column_A. MS SQL Server actually supports a four part name, with the fourth part being the database:
SELECT [MyDatabase].[StructureX].[Table].[Column_A] ...
Here, MyDatabase is the database name.
That same style works in MySQL, except you have to remember that schema and database are synonymous. So there, this:
SELECT `StructureX`.`Table`.`Column_A` ...
Would mean database StructureX, table Table, and column Column_A.
I Can say yes:
But instead of using table name, make a table some alias like this,
select a.column1 from yourTable as a
Using table alias is a good practice.
I'm working on a version control program, and I would like to implement database structure versioning as well.
Is there a way to get a list of all the queries that have altered the databse structure in any way?
For example I added a column to the 'users' table called 'remember_token'. Is there a way I can get the specific query that was executed on the MySQL server in order to add that column?
You may want to enable the mysql query log and then filter on ALTER queries or anything you need
The table names in my mysql database are dynamically generated. Is there some way to select data from tables which have a name matching a pattern? I guess it will look like:
select * from 'table_id_%'
No, you can't do that with MySQL. Tables in a query can't be dynamically specified - you have to build the list in your application (or do several single-table queries).
You can use INFORMATION_SCHEMA TABLES table to find tables you want, here is documentation: http://dev.mysql.com/doc/refman/5.0/en/tables-table.html . TABLES table has column NAME which represents names of tables. After finding table names you can run any sql queries you like.
That's not possible in the way you'd like to do it. However you could probably use prepared statements which are basically query-templates where you specificy the parameters (AFAIK also table names) that get replaced depending on your needs without copy and pasting the same query over and over again for different tables.
I have inserted new columns in one database, and I now want to add the same type of columns to a second database. I need to know which columns are in the first database that are not in the second. I have many tables in each database that needs column difference comparing. I searched the web and I can only find ways to see the difference of the contents of columns in two tables. I don't need to compare the contents, just different columns in all the tables in each database. Each database has the same tables.
Thanks!
I found that you can do a database dump that just has the structure from phpmyadmin.
Are you doing this manually? You could just use SHOW CREATE to see the structure of the tables, and then something like the diff command in Linux to compare them.
For a commercial product answer: I use Red Gate's SQL Compare which works great. It can compare the entire schema of two databases. It can also update your target database to match your source database.
Use redgate SQL compare to comapre schema of two tables.
sql-dbdiff works well too. Its an open source.