In MySQL, I'm trying to select rows from a table using a WHERE clause which is not fixed (known in advance), but instead is stored in another table and will be pulled from that other table at run-time.
Although seemingly similar questions already have been posted on Stackoverflow, there is none which exactly covers that problem.
What I'm trying to achieve is the following :
SELECT * FROM users WHERE (SELECT user_condition FROM user_condition_table WHERE id = '1')
The subquery
SELECT user_condition FROM user_condition_table WHERE id = '1'
Would produce the string
first_name like 'Br' and last_name like 'A%'
So the overall query would look like :
SELECT * FROM users WHERE first_name like 'Br' and last_name like 'A%'
I guess the problem here is that the returned string from select is returned as string and not as an SQL statement.
Is there any way to make that work?
You must use Dynamic SQL --> Prepare / Execute / Deallocate commands.
Dynamic SQL
Dynamic SQL is a programming technique that enables you to build SQL
statements dynamically at runtime. You can create more general
purpose, flexible applications by using dynamic SQL because the full
text of a SQL statement may be unknown at compilation.
Simple live example
DROP TABLE IF exists Users;
CREATE TABLE USERS(
first_name varchar(20),
last_name varchar(20)
);
INSERT INTO Users VALUES('Tom','Smile'),('Bob','Hamilton'),('Jane','Moon');
DROP TABLE IF exists user_condition_table;
CREATE TABLE user_condition_table(
id int,
user_condition Varchar(100)
);
INSERT INTO User_condition_table
VALUES(1, 'first_name like ''B%'' and last_name like ''H%''');
and the query:
SET #x = ( SELECT user_condition FROM user_condition_table WHERE id = '1');
SET #x = concat('SELECT * FROM USERS WHERE ', #x );
SELECT #x;
PREPARE stmt2 FROM #x;
EXECUTE stmt2;
DEALLOCATE PREPARE stmt2;
This is an interesting question. I have never tried it because I did such things in application code until now. Nevertheless, I got interested in the subject and just came up with the following solution:
SELECT #cond := user_condition FROM user_condition_table WHERE (id = 1);
SELECT #sqlstring := CONCAT('SELECT * FROM users WHERE ', #cond);
PREPARE sqlquery FROM #sqlstring;
EXECUTE sqlquery;
DEALLOCATE PREPARE sqlquery;
Some remarks:
It seems that you need to use session variables (denoted by the leading #).
This is not a stored procedure; it is just some normal SQL statements which you can type directly from within MySQL client, for example.
In MySQL Procedure I want count rows from a Temporary Table which created from a dynamic Query ie.
CREATE TEMPORARY TABLE IF NOT EXISTS tmp_Tbl as select * from dynamic_tbl;
Desc Temporary tmp_Tbl;
say Field have 15 Rows so save into a session variable #TotCols
again Create Temporary Table from a dynamic Query:
Desc Temporary tmp_Tbl;
say Field have 4 Rows so save into a session variable #TotCols
In the body of your stored routine, please try:
SET #create_tmp_table_sql = CONCAT(
'CREATE TEMPORARY TABLE IF NOT EXISTS tmp_tbl AS ',
'SELECT * FROM dynamic_tbl'
);
PREPARE create_tmp_table_stmt FROM #create_tmp_table_sql;
EXECUTE create_tmp_table_stmt;
DEALLOCATE PREPARE create_tmp_table_stmt;
SET #TotCols = (SELECT Count(*) FROM tmp_tbl);
I have a procedure that update a table. However, I need to back up the table each time prior updating it. So the only way I can backup the table via procedure is by create a table and inserting all the information from one table to another.
So What I need to do is create a table name with a random value to distinguish the different tables. The ideal solution will be "New_Table_Name_TIMESTAMP" so append timestamp to a string.
My Question is how to create a table with a timestamp added to it's name
New_table_name_201412301044
I have tried the following
DECLARE new_table varchar(100) DEFAULT '';
SET new_table = CONCAT('WORKFLOW_BU_', client_id_to_update, '_', unix_timestamp() );
CREATE TABLE data_import.new_table LIKE development.inventory_engine;
INSERT INTO data_import.new_table
SELECT * FROM development.inventory_engine;
but it create a table name called "new_table" and not the variable
Thanks
You're going to have to use so-called dynamic SQL, also known as "server side prepared statements" to do this. Ordinary SQL prohibits the use of variables for the names of tables or columns.
See here.
http://dev.mysql.com/doc/refman/5.0/en/sql-syntax-prepared-statements.html
sounds like a bad idea but you could do it with PREPARE statement FROM #sql and EXECUTE statement like this sqlFiddle
sample table
CREATE table yourTable(id int auto_increment primary key,value varchar(50));
INSERT into yourtable(value) values ('test1'),('test2'),('test3'),('test4');
create a table with a time_stamp ending (in the example I am only recording down to the HOUR, you can add _%i_%s to the formatting if you want it down to the seconds.
SET #TimeStamp = DATE_FORMAT(NOW(),'%Y_%m_%d_%H');
SET #sql = CONCAT('CREATE table yourTable',#TimeStamp,'(id int auto_increment primary key,value varchar(50))');
PREPARE statement FROM #sql;
EXECUTE statement;
SET #sql = CONCAT('INSERT INTO yourTable',#TimeStamp,'(id,value) SELECT id,value FROM yourTable');
PREPARE statement FROM #sql;
EXECUTE statement;
I have a lot of delete queries but in some production databases some table is not found. I need simple decision on this problem.
Queries like
DELETE b.* FROM `table` b
JOIN `another_table` u
ON u.key2 = b.key
WHERE u.key3 <> ?
I need something like:
IF TABLE `table` EXISTS DELETE b.* FROM `table` b ...
If you need to delete the rows of a table if that latter exists, you will have to rely on a custom stored procedure I think. something like that:
-- Define the procedure
CREATE PROCEDURE delete_if_exists(IN tbl CHAR(80))
BEGIN
IF #tbl IN (select table_name from information_schema.tables where table_schema = "db_2_44afb7")
THEN
SET #query = CONCAT("DELETE FROM ", #tbl);
PREPARE stmt FROM #query;
EXECUTE stmt;
END IF;
END //
-- use it
CALL delete_if_exists("mytable");
CALL delete_if_exists("myothertable");
See http://sqlfiddle.com/#!2/2ee190/3 for an example.Of course, you could adjust the "DELETE FROM",... part to fit with your specific needs.
You can enclose the SELECT query on the table before using the DROP...
IF EXISTS(SELECT table.records FROM table WHERE ...)
DELETE records_names FROM ...
From what it sounds like IF EXISTS(select query here) before your delete command is what you're looking for? I'm a postgresql guy so please excuse the SQL errors if they exist.
More examples in this post.
How do I copy or clone or duplicate the data, structure,
and indices of a MySQL table to a new one?
This is what I've found so far.
This will copy the data and the structure,
but not the indices:
create table {new_table} select * from {old_table};
This will copy the structure and indices,
but not the data:
create table {new_table} like {old_table};
To copy with indexes and triggers do these 2 queries:
CREATE TABLE new_table LIKE old_table;
INSERT INTO new_table SELECT * FROM old_table;
To copy just structure and data use this one:
CREATE TABLE new_table AS SELECT * FROM old_table;
I've asked this before:
Copy a MySQL table including indexes
Apart from the solution above, you can use AS to make it in one line.
CREATE TABLE tbl_new AS SELECT * FROM tbl_old;
MySQL way:
CREATE TABLE recipes_new LIKE production.recipes;
INSERT recipes_new SELECT * FROM production.recipes;
Go to phpMyAdmin and select your original table then select "Operations" tab in the "Copy table to (database.table)" area. Select the database where you want to copy and add a name for your new table.
I found the same situation and the approach which I took was as follows:
Execute SHOW CREATE TABLE <table name to clone> : This will give you the Create Table syntax for the table which you want to clone
Run the CREATE TABLE query by changing the table name to clone the table.
This will create exact replica of the table which you want to clone along with indexes. The only thing which you then need is to rename the indexes (if required).
The better way to duplicate a table is using only DDL statement. In this way, independently from the number of records in the table, you can perform the duplication instantly.
My purpose is:
DROP TABLE IF EXISTS table_name_OLD;
CREATE TABLE table_name_NEW LIKE table_name;
RENAME TABLE table_name TO table_name_OLD;
RENAME TABLE table_name _NEW TO table_name;
This avoids the INSERT AS SELECT statement that, in case of table with a lot of records can take time to be executed.
I suggest also to create a PLSQL procedure as the following example:
DELIMITER //
CREATE PROCEDURE backup_table(tbl_name varchar(255))
BEGIN
-- DROP TABLE IF EXISTS GLS_DEVICES_OLD;
SET #query = concat('DROP TABLE IF EXISTS ',tbl_name,'_OLD');
PREPARE stmt FROM #query;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
-- CREATE TABLE GLS_DEVICES_NEW LIKE GLS_DEVICES;
SET #query = concat('CREATE TABLE ',tbl_name,'_NEW LIKE ',tbl_name);
PREPARE stmt FROM #query;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
-- RENAME TABLE GLS_DEVICES TO GLS_DEVICES_OLD;
SET #query = concat('RENAME TABLE ',tbl_name,' TO ',tbl_name,'_OLD');
PREPARE stmt FROM #query;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
-- RENAME TABLE GLS_DEVICES_NEW TO GLS_DEVICES;
SET #query = concat('RENAME TABLE ',tbl_name,'_NEW TO ',tbl_name);
PREPARE stmt FROM #query;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
END//
DELIMITER ;
Have a nice day!
Alex
To duplicate a table and its structure without data from a different a database use this. On the new database sql type
CREATE TABLE currentdatabase.tablename LIKE olddatabase.tablename
Worths to mention the importance of checking if the table already exists before
trying to duplicate it:
CREATE TABLE IF NOT EXISTS new_table LIKE old_table;
INSERT new_table
SELECT * FROM old_table;
As was said by the previous answers this will copy structure, data and
all the dependent objects of the table.
See MySql Tutorial:
Expanding on this answer one could use a stored procedure:
CALL duplicate_table('tableName');
Which will result in a duplicate table called tableName_20181022235959 If called when
SELECT NOW();
results:
2018-10-22 23:59:59
Implementation
DELIMITER $$
CREATE PROCEDURE duplicate_table(IN tableName VARCHAR(255))
BEGIN
DECLARE schemaName VARCHAR(255) DEFAULT SCHEMA();
DECLARE today VARCHAR(14) DEFAULT REPLACE(REPLACE(REPLACE(NOW(), '-', ''), ' ', ''), ':', ''); -- update # year 10000
DECLARE backupTableName VARCHAR(255) DEFAULT CONCAT(tableName, '_', today);
IF fn_table_exists(schemaName, tableName)
THEN
CALL statement(CONCAT('CREATE TABLE IF NOT EXISTS ', backupTableName,' LIKE ', tableName));
CALL statement(CONCAT('INSERT INTO ', backupTableName,' SELECT * FROM ', tableName));
CALL statement(CONCAT('CHECKSUM TABLE ', backupTableName,', ', tableName));
ELSE
SELECT CONCAT('ERROR: Table "', tableName, '" does not exist in the schema "', schemaName, '".') AS ErrorMessage;
END IF;
END $$
DELIMITER ;
DELIMITER $$
CREATE FUNCTION fn_table_exists(schemaName VARCHAR(255), tableName VARCHAR(255))
RETURNS TINYINT(1)
BEGIN
DECLARE totalTablesCount INT DEFAULT (
SELECT COUNT(*)
FROM information_schema.TABLES
WHERE (TABLE_SCHEMA COLLATE utf8_general_ci = schemaName COLLATE utf8_general_ci)
AND (TABLE_NAME COLLATE utf8_general_ci = tableName COLLATE utf8_general_ci)
);
RETURN IF(
totalTablesCount > 0,
TRUE,
FALSE
);
END $$
DELIMITER ;
DELIMITER $$
CREATE PROCEDURE statement(IN dynamic_statement TEXT)
BEGIN
SET #dynamic_statement := dynamic_statement;
PREPARE prepared_statement FROM #dynamic_statement;
EXECUTE prepared_statement;
DEALLOCATE PREPARE prepared_statement;
END $$
DELIMITER ;
After I tried the solution above, I come up with my own way.
My solution a little manual and needs DBMS.
First, export the data.
Second, open the export data.
Third, replace old table name with new table name.
Fourth, change all the trigger name in the data (I use MySQL and it show error when I don't change trigger name).
Fifth, import your edited SQL data to the database.
To create table structure only use this below code :
CREATE TABLE new_table LIKE current_table;
To copy data from table to another use this below code :
INSERT INTO new_table SELECT * FROM current_table;
Simple Cloning:
it create a table from another table without taking into account any column attributes and indexes.
CREATE TABLE new_table SELECT * FROM original_table;
Shallow Cloning:
This will only create an empty table base on the structure of the original table
CREATE TABLE new_table LIKE original_table;
The following command would create an empty table base on the original table.
CREATE TABLE adminUsers LIKE users;
Deep Cloning:
This means the new table gets to have all the attributes of each column and indexes of the existing table. This quite useful if you want to maintain the indexes and attributes of the existing table.
CREATE TABLE new_table LIKE original_table;
INSERT INTO new_table SELECT * FROM original_table;
https://towardsdatascience.com/how-to-clone-tables-in-sql-dd29586ec89c
// To copy specific column data use this one:
CREATE TABLE ut_axis_existrec LIKE ut_karvy_annexure; // To create new table
INSERT INTO ut_axis_existrec
(funding_ac,micr_no, warrant_no,
amount,invname,mfundcode,funding_dt,status,remarks1,amc_remark,created_at)
SELECT
t1.funding_ac,
t1.micr_no,
t1.warrant_no,
t1.amount,
t1.invname,
t1.mfund_code,
t1.funding_dt,
t1.status,
t1.remarks1,
t1.created_at
from ut_axis_karvy
inner join
ut_axis_karvy_master as t2
on t1.micr_no = t2.micr_no;
Try this :
`CREATE TABLE new-table (id INT(11) auto_increment primary key) SELECT old-table.name, old-table.group, old-table.floor, old-table.age from old-table;`
I selected 4 columns from old-table and made a new table.
FOR MySQL
CREATE TABLE newtable LIKE oldtable ;
INSERT newtable SELECT * FROM oldtable ;
FOR MSSQL
Use MyDatabase:
Select * into newCustomersTable from oldCustomersTable;
This SQL is used for copying tables, here the contents of oldCustomersTable will be copied to newCustomersTable.
Make sure the newCustomersTable does not exist in the database.