MySQL add column if not exist - mysql

Question

IF NOT EXISTS (SELECT * FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'email_subscription' AND COLUMN_NAME = 'subscribe_all')
THEN
ALTER TABLE email_subscription
ADD COLUMN subscribe_all TINYINT(1) DEFAULT 1,
ADD COLUMN subscribe_category varchar(512) DEFAULT NULL;
I had a look at huge amount of examples. but this query doesn't work, I got error of:
ERROR 1064 (42000): You have an error in your SQL syntax; check the
manual that corresponds to your MySQL server version for the right
syntax to use near 'IF NOT EXISTS (SELECT * FROM
INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME =' at line 1

Answer 1

If your host doesn't give you permission to create or run procedures, I think I found another way to do this using PREPARE/EXECUTE and querying the schema:
SET #s = (SELECT IF(
(SELECT COUNT(*)
FROM INFORMATION_SCHEMA.COLUMNS
WHERE table_name = 'table_name'
AND table_schema = DATABASE()
AND column_name = 'col_name'
) > 0,
"SELECT 1",
"ALTER TABLE table_name ADD col_name VARCHAR(100)"
));
PREPARE stmt FROM #s;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

Answer 2

you can create a procedure for the query,
DELIMITER $$
CREATE PROCEDURE Alter_Table()
BEGIN
DECLARE _count INT;
SET _count = ( SELECT COUNT(*)
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'email_subscription' AND
COLUMN_NAME = 'subscribe_all');
IF _count = 0 THEN
ALTER TABLE email_subscription
ADD COLUMN subscribe_all TINYINT(1) DEFAULT 1,
ADD COLUMN subscribe_category varchar(512) DEFAULT NULL;
END IF;
END $$
DELIMITER ;

Answer 3

There is no equivalent syntax to achieve this in a single MySQL statement.
To get something simlilar, you can either
1) attempt to add the column with an ALTER TABLE, and let MySQL raise an error if a column of that name already exists in the table, or
2) query the information_schema.columns view to check if a column of that name exists in the table.
Note that you really do need to check for the table_schema, as well as the table_name:
SELECT column_name
FROM information_schema.columns
WHERE table_schema = 'foo'
AND table_name = 'email_subscription'
AND column_name = 'subscribe_all'
and based on that, decide whether to run the ALTER TABLE

Answer 4

You are using MS SQL Server syntax in MySQL.

Answer 5

Also add condition for database name to check column existance.
Try this:
DELIMITER $$
CREATE PROCEDURE sp_AlterTable()
BEGIN
IF NOT EXISTS (SELECT * FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_SCHEMA = 'dbName' AND
TABLE_NAME = 'email_subscription' AND
COLUMN_NAME = 'subscribe_all') THEN
ALTER TABLE email_subscription
ADD COLUMN subscribe_all TINYINT(1) DEFAULT 1,
ADD COLUMN subscribe_category VARCHAR(512) DEFAULT NULL;
END IF;
END $$
DELIMITER ;

Answer 6

SET #s = (SELECT IF(
(SELECT COUNT(column_name)
FROM INFORMATION_SCHEMA.COLUMNS
WHERE table_name = 'oc_bitcoin_wallets_receive'
AND table_schema = 'k_opencart2'
AND column_name = 'test3'
) > 0,
"SELECT 1",
"ALTER TABLE `oc_bitcoin_wallets_receive` ADD COLUMN `test3` INT NOT NULL AFTER `test2`;"
));
PREPARE stmt FROM #s;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
Values for edit:
oc_bitcoin_wallets_receive - table name,
k_opencart2 - database name,
test3 - name of new column,
oc_bitcoin_wallets_receive - second location table
test3 - second location column,
test2 - name of column before new column.