How can i count tables which starts with special prefix in MYSQL database?
I have below syntax below for showing table names which starts with prefix:
SHOW TABLES LIKE 'prefix\_%'
However i don't know how to count number of these tables.
I think below SQL useful to you.Change your database name and prefix value.
SELECT count(table_name) FROM information_schema.tables
WHERE table_type = 'base table' AND table_schema='database_name' AND table_name LIKE "prefix\_%";
Thank you.
Related
I have multiple tables in my multiple databases.
On different servers, i use MySQL / PostgreSQL / MS SQL.
I keep short table namesbut the comments given to the tables are with full explanation.
I want query that will show me tables ending with "com" and also the comment given to each table (table's comment).
In MySQL, I know:
SELECT table_name FROM information_schema.tables where table_name like "%com"
But this shows all tables from all databases.
For MySQL, check out following:
SELECT table_name FROM information_schema.tables;
will show all table names in all databases;
SELECT table_name,table_comment FROM information_schema.tables
will show all table names + comment in all databases;
interesting thing, you can fire
SELECT * FROM information_schema.tables;
to know what all info you can get of a table.
SELECT table_name,table_comment FROM information_schema.tables
where
table_schema = 'sifr_b';
will show all table names + comment in "sifr_b" database;
SELECT table_name,table_comment FROM information_schema.tables
where
table_schema = 'sifr_b' and
table_name like "%com";
will show those table names + comment in "sifr_b" database, that have table name ending with "com";
I have 2 versions of a database (say db_dev and db_beta). I've made some changes in the db_dev database - added some tables, and changed a few columns in some existing tables. I need to find out the list of table names in which changes have been made.
I can easily find out the tables I've added by running the following query on the information_schema database:
SELECT table_name
FROM tables
WHERE table_schema = 'db_dev'
AND table_name NOT IN (SELECT table_name
FROM tables
WHERE table_schema = 'db_beta');
How do I get the table_names whose column_names do not match in the two database versions?
There are many ready made tools available which can give you changed schema by comparing two databases. Here are some tools which can serve your purpose :
Red-Gate's MySQL Schema & Data Compare
Maatkit
MySQL Diff
SQL EDT
Red-Gate's MySQL Compare is best tool for this purpose. Its paid though but they provide 14 days free trial version if you want to do something temporary.
Using information_schema, here is how it works.
First, you know that the information_schema.COLUMNS table contains the columns definition. If one column has been changed, or a table does not exist, it will reflect in the information_schema.COLUMNS table.
Difficult part is that you have to compare all columns of your COLUMNS table. So, you have to select TABLE_CATALOG,TABLE_NAME,COLUMN_NAME,ORDINAL_POSITION,COLUMN_DEFAULT, and so on (which is subject to evolution depending on your MySQL version).
The column list is the result of the following query:
SELECT GROUP_CONCAT(column_name)
FROM information_schema.COLUMNS
WHERE table_schema="information_schema"
AND table_name="COLUMNS" AND column_name!='TABLE_SCHEMA';
After that, we just have to SELECT TABLE_NAME, <column_list> and search for columns which appear once (column inexistent in other table), or where columns have two different definitions (columns altered). So we will have two different count in the resulting query to consider the two cases.
We will so use a prepared statement to retrieve the list of column we want, and grouping the result.
The resulting query does all the process for you:
SELECT CONCAT(
"SELECT DISTINCT TABLE_NAME
FROM information_schema.COLUMNS
WHERE TABLE_SCHEMA IN('db_dev', 'db_beta')
GROUP BY table_name, COLUMN_NAME
HAVING count(*)=1 OR
COUNT(DISTINCT CONCAT_WS(',', NULL, ",
GROUP_CONCAT(column_name)
,"))=2;")
FROM information_schema.COLUMNS
WHERE table_schema="information_schema"
AND table_name="COLUMNS" AND column_name!='TABLE_SCHEMA'
INTO #sql;
PREPARE stmt FROM #sql;
EXECUTE #sql;
The following solution does not use an sql query like you tried and does not give you a real list of tables, but it shows you all the changes in both databases.
You can do an sql dump of both database structures :
mysqldump -u root -p --no-data dbname > schema.sql
Then you can compare both files, e.g. using the diff linux tool.
I have a column 'seq' in every table of my database that I would like to delete easily.
I have to do this on occasion in MySQL and am hoping this can be automated.
There isn't a simple magical expression to just do this. You need to generate a list of SQL statements and then run them, somehow.
(Most database folks don't routinely drop columns from a database in production; it takes a lot of time during which the tables are inaccessible, and it's destructive. A fat-finger error could really mess you up.)
You might start by using the information_schema in MySQL to discover which of your tables have a seq column in them. This query will return that list of tables for the database you're currently using.
SELECT DISTINCT TABLE_NAME
FROM information_schema.COLUMNS
WHERE TABLE_SCHEMA = DATABASE()
AND COLUMN_NAME = 'seq'
You could then adapt that query to, for example, create a list of statements like this.
SELECT DISTINCT
CONCAT('UPDATE ',TABLE_NAME, ' SET seq = 0;') AS stmt
FROM information_schema.COLUMNS
WHERE TABLE_SCHEMA = DATABASE()
AND COLUMN_NAME = 'seq'
This will produce a result set like this:
UPDATE table_a SET seq = 0;
UPDATE table_b SET seq = 0;
UPDATE user SET seq = 0;
Then you could run these statements one by one. These statements will zero out your seq columns.
Edit
You can also do
CONCAT('ALTER TABLE ',TABLE_NAME, ' DROP COLUMN seq;') AS stmt
to get a drop column statement for each table.
But, you might consider creating views of your tables that don't contain the seq columns, and then exporting to PostgreSQL using those views. If your tables are significant in size, this will save you a lot of time.
I have a Microsoft stored procedure that queries two MySQL databases using OpenQuery. The two MySQL databases should be have the same schemas, so I can run the same query on both.
However, we will soon alter the MySQL schemas, and add a column to a table. But the two MySQL databases won't happen at the same time, and I don't know the exact date of the releases.
I therefore want to write the query so that if the new column exists, then I use it in my select. If not, then I use a default value.
Is this possible? (That is have a query that handles differences in the table schema?)
(Not to be confused with 'coelesce' where the field definitely exists, but is simply null.)
You can use the following SELECT statement:
SELECT *
FROM information_schema.COLUMNS
WHERE
TABLE_SCHEMA = 'database name' AND TABLE_NAME = 'your table name'
AND COLUMN_NAME = 'the column name you want to check for'
If the above returns a value, your column is there. If not, then run your alternative SELECT statement
Updated statement:
IF EXISTS (SELECT *
FROM OPENQUERY(servername, 'SELECT *
FROM information_schema.COLUMNS
WHERE TABLE_SCHEMA = ''database name''
AND TABLE_NAME = ''your table name''
AND COLUMN_NAME = ''the column name you want to check for'' ))
I'm looking to replace all occurrences of characters in all columns of all tables in my database.
I got the name of my column like this:
select table_name, column_name from information_schema.columns;
And I would apply an UPDATE REPLACE like this:
update table_name set column_name = replace (column_name, "a", "A");
PS : The replacement of "a" to "A" is just one example, my problem is rather how to link table_name and column_name between my two queries.
I tried with subselect, like:
update (select table_name from information_schema.tables as tables) set (select column_name from columns as information_schema.columns Where table_name = tables) = replace (columns, "a", "A");
But I still get errors when I try. What is the right way to do this?
Thank you in advance.
What you need is a stored procedure that will use the information_schema to find all tables and columns within your database, and execute an update statement for all these tables.
Have a look at the following question which answers exactly what you wish to do: Find and replace in entire mysql database
It will not work like that.
You have 2 options:
1) Iterate through all tables on code side and lunch the update for each one
2) Use a stored procedure that iterate through all tables and lunch the update for each one