Truncate in multiple tables - mysql

I'm trying to create a way for me to apply truncate across multiple tables at the same time.
I tried the following code:
SELECT CONCAT('TRUNCATE TABLE ',table_schema,'.',TABLE_NAME, ';')
FROM INFORMATION_SCHEMA.TABLES
WHERE table_schema in ('mytable1','mytable2','mytable3');
More unsuccessfully, it is not truncating the tables.
Does anyone know of any way to do this?


DECLARE #CODE NVARCHAR(MAX) = '', #XML XML
SET #XML = STUFF((
SELECT ' ' + data.CODE_DELETE
FROM (
SELECT CONCAT ('TRUNCATE TABLE ', table_schema, '.', TABLE_NAME, '') AS CODE_DELETE
FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_NAME IN ('CITY', 'WORKERS')
) [data]
FOR XML PATH('')
), 1, 1, '')
SET #CODE = CAST(#XML AS VARCHAR(MAX))
SELECT #CODE
EXECUTE sp_executesql #CODE;
the variable #XML is to be able to convert the rows into a single value, then we must convert the sql code to varchar in order to execute it with
EXECUTE sp_executesql #CODE;
you can see the code that will be executed if you do this:
SELECT #CODE
city ​​and workers are tables that I have in my database, if you look I change table_schema by TABLE_NAME in the WHERE clause.


Please use transaction to do it if you want to keep it atomic.
START TRANSACTION;
// Your truncate statements;
COMMIT;

Related

how to get data from dynamic table in sql

How can I get data from chosen table of my database?
I'm going to work with database in c# application and I have the database includes that tables:
MyTable1;
MyTable2;
...
And I have tbl variable that is equal to tbl = "MyTable2";. I want to execute the code as following:select * from tbl
I try to execute this code:
SELECT *
FROM (
SELECT TABLE_NAME
FROM information_schema.tables
WHERE TABLE_NAME = 'MyTable1'
);
But the code returned error that Every derived table must have its own alias
I want to get all data from table whose name is equal to my variable (tbl) and its value can also be changed. How can I do it?

You might be able to do this using a prepared statement in MySQL:
SELECT TABLE_NAME
INTO #table
FROM information_schema.tables
WHERE TABLE_NAME = 'MyTable1';
SET #query = CONCAT('SELECT * FROM ', #table);
PREPARE stmt FROM #query;
EXECUTE stmt;

SELECT *
FROM (
SELECT TABLE_NAME
FROM information_schema.tables
WHERE TABLE_NAME = 'MyTable1'
) AS Blah

Try this:
DECLARE #SELECT nvarchar(500)
SET #SELECT = 'SELECT * FROM ' + #tbl
EXECUTE sp_executesql #SELECT

MySQL Select columns where the column name contains a substring

I have a table with a lot of fields about a person and then several recommendations of other people.
They are named:
"recommendation_1_name" "recommendation_1_company" 'recommendation_1_contact"
"recommendation_2_name" "recommendation_2_company" "recommendation_2_contact"
and so on.
I am trying to come up with a statement that allows me to only get the recommendations.
I imported an excel file into the table so it's just one large table.
This is what I have and it is returning an Empty set.
select * from questionnaire where 'COLUMN_NAME' like '%recommendation%';
I've been playing around with it making a table with only the recommendation fields and it still doesn't return anything.

Mysql: select recommendation_1_name, recommendation_2_name etc... from (table) where (USER) = (USERID) or however you can uniquely identify that user.

This Query generates you dynamic a SELECT query with all fields like 'recommendation%'. You only must setup the Databasename, and the Tablename. You can directly query the result of my query or add the WHERE clause.
SELECT
CONCAT( 'SELECT ',
GROUP_CONCAT(COLUMN_NAME SEPARATOR ',\n')
)
FROM information_schema.columns
WHERE TABLE_SCHEMA = 'DBNAME'
AND TABLE_NAME = 'TABLENAME'
AND COLUMN_NAME LIKE 'recommendation%';

You really need to normalize your schema.
But just as an experiment and example for some other cases (maybe somebody really need it). Here is solution to get this case resolved using stored procedure:
CREATE PROCEDURE `get_recommendations`()
BEGIN
DECLARE Q VARCHAR(100);
DECLARE C_NAME VARCHAR(100);
DECLARE cur CURSOR FOR SELECT GROUP_CONCAT(column_name) as `columns`
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_SCHEMA = 'test'
AND TABLE_NAME ='questionnaire'
AND COLUMN_NAME LIKE '%recommendation%'
;
SET Q = 'SELECT ';
OPEN cur;
FETCH cur INTO C_NAME;
SET Q = CONCAT(Q,C_NAME,' ');
CLOSE cur;
SET #Q = CONCAT(Q,'FROM questionnaire;');
PREPARE stmt FROM #Q;
EXECUTE stmt ;
END
Don't forget to replace TABLE_SCHEMA = 'test' with your real database name.

Mysql UNION with dynamic query

i have the following problem. I inherited a software that uses a database prefix for every customer.
All tables have the same structure and columns. For a data migration to new version i want to union all these tables
and set a customer foreign key instead and get rid of all the subtables. i'm looking for a way to create
a view for this task because i also want to stay backwards compatible for now.
I found this dynamic query which seems to do what i want
but i can't execute on my mysql server. I assume it was written for another sql server.
The table name structure is (about 80 customer tables):
customer1_faxe
customer2_faxe
customer3_faxe
customer4_faxe
...
How would you approach this problem?
DECLARE #SelectClause VARCHAR(100) = 'SELECT *'
,#Query VARCHAR(1000) = ''
SELECT #Query = #Query + #SelectClause + ' FROM ' + TABLE_NAME + ' UNION ALL '
FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_NAME LIKE '%_faxe'
SELECT #Query = LEFT(#Query, LEN(#Query) - LEN(' UNION ALL '))
EXEC (#Query)

This query is using SQL Server syntax. You need something like this:
declare #SelectClause varchar(8000);
declare #Query varchar(8000);
set #SelectClause = 'SELECT *';
SELECT #Query := group_concat(#SelectClause, ' FROM ', TABLE_NAME SEPARATOR ' UNION ALL ')
FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_NAME LIKE '%_faxe';
prepare stmt from #Query;
execute stmt;
Note that the group_concat() with separator simplifies the logic.

Cursor is becoming an never ending loop

I want to create an SP to generate the metadata for all tables using cursors in SQL. Following is the code I have tried. but its becoming a never ending loop and same data is repeated. Thanks in advance.
--SELECT * FROM information_schema.columns
ALTER PROCEDURE p1
AS
SET NOCOUNT ON;
DECLARE #id INT
, #tablename VARCHAR(100)
, #columnname VARCHAR(100)
, #datatype VARCHAR(100)
, #isnullable VARCHAR(100)
BEGIN
DECLARE CURSOR_1 CURSOR FOR
SELECT TABLE_NAME
, COLUMN_NAME
, DATA_TYPE
, IS_NULLABLE
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'Employee' -- group BY table_name
OPEN CURSOR_1
FETCH NEXT FROM CURSOR_1 INTO
#tablename,
#columnname,
#datatype,
#isnullable
WHILE ##fetch_status = 0
BEGIN
INSERT INTO table_schema_detail (TABLE_NAME, COLUMN_NAME, DATA_TYPE, isnullable)
VALUES (#tablename, #columnname, #datatype, #isnullable)
END
FETCH NEXT FROM CURSOR_1 INTO
#tablename,
#columnname,
#datatype,
#isnullable
CLOSE CURSOR_1
DEALLOCATE CURSOR_1
SET NOCOUNT OFF;
END
GO

I don't really understand why you need to store this information on a table, since it's already available on the system views (and if you still need to store this data, why are you using a cursor?). If, like your comment says, you need to store data from 3 tables, then you could simply do:
INSERT INTO table_schema_detail(table_name,column_name,data_type,isnullable)
SELECT table_name, column_name, data_type, is_nullable
FROM INFORMATION_SCHEMA.COLUMNS
WHERE table_name IN ('Employee','OtherTable1','OtherTable2')
But again, I don't see the point. At least you could store the date when this was done:
INSERT INTO table_schema_detail(table_name,column_name,data_type,isnullable,DateInserted)
SELECT table_name, column_name, data_type, is_nullable, GETDATE()
FROM INFORMATION_SCHEMA.COLUMNS
WHERE table_name IN ('Employee','OtherTable1','OtherTable2')

look where you have that end statement
insert INTO table_schema_detail(table_name,column_name,data_type,isnullable) VALUES(#tablename,#columnname,#datatype,#isnullable)
end
Suspect it never gets to this line
FETCH NEXT FROM CURSOR_1 into
And agree with other comments on is a cursor the proper approach but this is an answer to the question as stated.

I think get meta-data from sys.columns more preferable (in your case, cursor is not necessary):
INSERT INTO dbo.table_schema_detail
(
TABLE_NAME
, COLUMN_NAME
, DATA_TYPE
, IS_NULLABLE
)
SELECT
SCHEMA_NAME(o.[schema_id]) + '.' + o.name
, c.name
, TYPE_NAME(c.system_type_id)
, c.is_nullable
FROM sys.columns c
JOIN sys.objects o ON c.[object_id] = o.[object_id]
WHERE SCHEMA_NAME(o.[schema_id]) + '.' + o.name = 'dbo.Employee'
AND o.[type] = 'U'

Lower case column names when using SELECT

I'm using the Kohana framework and I need to convert column names to lowercase. I don't have control of the db table structure. I want to do the following:
SELECT LOWER(*) FROM .....
but MYSQL does not like that. Whats the proper way of outputting the lower case column names if I don't know what the column names will be?

Found here http://dev.mysql.com/doc/refman/5.0/en/columns-table.html
SELECT LOWER(COLUMN_NAME)
FROM INFORMATION_SCHEMA.COLUMNS
WHERE table_name = 'Table'
Below you can see both MSSQL and MySQL syntax for creating a dynamic query using the column results from the query above.
MSSQL Syntax
DECLARE #ColumnNames [nvarchar](1024)
SELECT #ColumnNames = COALESCE(#ColumnNames + ', ', '') + LOWER(COLUMN_NAME)
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'Table'
DECLARE #Sql [nvarchar](1024) = 'SELECT ' + #ColumnNames + ' FROM Table ' --Remember to put spaces after SELECT and before FROM
EXEC(#Sql)
With this you are dynamically building your query and then executing it.
MySQL Syntax
SELECT #ColumnNames := GROUP_CONCAT(LOWER(COLUMN_NAME))
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'Table';
SET #Sql = CONCAT('SELECT ', #ColumnNames, ' FROM Table ');
PREPARE stmt1 FROM #Sql;
EXECUTE stmt1;