如果列不存在，则为 MySQL: ALTERTABLE

我有这个密码:

ALTER TABLE `settings`
ADD COLUMN `multi_user` TINYINT(1) NOT NULL DEFAULT 1

我只想在这个列不存在的情况下修改这个表。

我尝试了很多不同的方法，但没有一个奏效:

ALTER TABLE `settings`
ADD COLUMN IF NOT EXISTS `multi_user` TINYINT(1) NOT NULL DEFAULT 1

程序如下:

DELIMITER $$
CREATE PROCEDURE Alter_Table()
BEGIN
DECLARE _count INT;
SET _count = (  SELECT COUNT(*)
FROM INFORMATION_SCHEMA.COLUMNS
WHERE   TABLE_NAME = 'settings' AND
COLUMN_NAME = 'multi_user');
IF _count = 0 THEN
ALTER TABLE `settings` ADD COLUMN `multi_user` TINYINT(1) NOT NULL DEFAULT 1
END IF;
END $$
DELIMITER ;

我在 END IF 中得到错误，然后在 END 中得到错误，然后在1中得到错误

我该怎么做才能让事情尽可能简单呢？

244230 次浏览
小开

hope this will help you

SELECT COLUMN_NAME
FROM INFORMATION_SCHEMA.COLUMNS
WHERE table_name = 'tbl_name'
AND table_schema = 'db_name'
AND column_name = 'column_name'

or

delimiter '//'


CREATE PROCEDURE addcol() BEGIN
IF NOT EXISTS(
SELECT * FROM information_schema.COLUMNS
WHERE COLUMN_NAME='new_column' AND TABLE_NAME='tablename' AND TABLE_SCHEMA='the_schema'
)
THEN
ALTER TABLE `the_schema`.`the_table`
ADD COLUMN `new_column` TINYINT(1) NOT NULL DEFAULT 1;;


END IF;
END;
//


delimiter ';'


CALL addcol();


DROP PROCEDURE addcol;
小开
最佳答案

Use the following in a stored procedure:

IF NOT EXISTS( SELECT NULL
FROM INFORMATION_SCHEMA.COLUMNS
WHERE table_name = 'tablename'
AND table_schema = 'db_name'
AND column_name = 'columnname')  THEN


ALTER TABLE `TableName` ADD `ColumnName` int(1) NOT NULL default '0';


END IF;
小开

Use PREPARE/EXECUTE and querying the schema. The host doesn't need to have permission to create or run procedures :

SET @dbname = DATABASE();
SET @tablename = "tableName";
SET @columnname = "colName";
SET @preparedStatement = (SELECT IF(
(
SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS
WHERE
(table_name = @tablename)
AND (table_schema = @dbname)
AND (column_name = @columnname)
) > 0,
"SELECT 1",
CONCAT("ALTER TABLE ", @tablename, " ADD ", @columnname, " INT(11);")
));
PREPARE alterIfNotExists FROM @preparedStatement;
EXECUTE alterIfNotExists;
DEALLOCATE PREPARE alterIfNotExists;
小开

Here is a solution that does not involve querying INFORMATION_SCHEMA, it simply ignores the error if the column does exist.

DROP PROCEDURE IF EXISTS `?`;
DELIMITER //
CREATE PROCEDURE `?`()
BEGIN
DECLARE CONTINUE HANDLER FOR SQLEXCEPTION BEGIN END;
ALTER TABLE `table_name` ADD COLUMN `column_name` INTEGER;
END //
DELIMITER ;
CALL `?`();
DROP PROCEDURE `?`;

P.S. Feel free to give it other name rather than ?

小开 
SET @dbname = DATABASE();
SET @tablename = "table";
SET @columnname = "fieldname";
SET @preparedStatement = (SELECT IF(
(
SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS
WHERE
(table_name = @tablename)
AND (table_schema = @dbname)
AND (column_name = @columnname)
) > 0,
"SELECT 1",
CONCAT("ALTER TABLE ", @tablename, " ADD ", @columnname, " DECIMAL(18,4) NULL;")
));
PREPARE alterIfNotExists FROM @preparedStatement;
EXECUTE alterIfNotExists;
DEALLOCATE PREPARE alterIfNotExists;
小开

I used this approach (Without using stored procedure):

SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'tbl_name' AND COLUMN_NAME = 'column_name'

If it didnt return any rows then the column doesn't exists then alter the table:

ALTER TABLE tbl_name ADD COLUMN column_name TINYINT(1) NOT NULL DEFAULT 1

Hope this helps.

小开

Add field if not exist:

CALL addFieldIfNotExists ('settings', 'multi_user', 'TINYINT(1) NOT NULL DEFAULT 1');

addFieldIfNotExists code:

DELIMITER $$


DROP PROCEDURE IF EXISTS addFieldIfNotExists
$$


DROP FUNCTION IF EXISTS isFieldExisting
$$


CREATE FUNCTION isFieldExisting (table_name_IN VARCHAR(100), field_name_IN VARCHAR(100))
RETURNS INT
RETURN (
SELECT COUNT(COLUMN_NAME)
FROM INFORMATION_SCHEMA.columns
WHERE TABLE_SCHEMA = DATABASE()
AND TABLE_NAME = table_name_IN
AND COLUMN_NAME = field_name_IN
)
$$


CREATE PROCEDURE addFieldIfNotExists (
IN table_name_IN VARCHAR(100)
, IN field_name_IN VARCHAR(100)
, IN field_definition_IN VARCHAR(100)
)
BEGIN


SET @isFieldThere = isFieldExisting(table_name_IN, field_name_IN);
IF (@isFieldThere = 0) THEN


SET @ddl = CONCAT('ALTER TABLE ', table_name_IN);
SET @ddl = CONCAT(@ddl, ' ', 'ADD COLUMN') ;
SET @ddl = CONCAT(@ddl, ' ', field_name_IN);
SET @ddl = CONCAT(@ddl, ' ', field_definition_IN);


PREPARE stmt FROM @ddl;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;


END IF;


END;
$$
小开 
$sql="SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'Your_Table_Name' AND COLUMN_NAME = 'Your_New_Column_Name'";
$RESULT = mysqli_query($conn,$sql);

The abobe query return 0 if the column is not present in your table then you need to run alter query like below

if($RESULT){
$sqll="ALTER TABLE Your_table_Name ADD COLUMN Your_New_Column_Name varchar(20) NOT NULL DEFAULT 0";
}
小开

Sometimes it may happen that there are multiple schema created in a database.

So to be specific schema we need to target, so this will help to do it.

SELECT count(*) into @colCnt FROM information_schema.columns WHERE table_name = 'mytable' AND column_name = 'mycolumn' and table_schema = DATABASE();
IF @colCnt = 0 THEN
ALTER TABLE `mytable` ADD COLUMN `mycolumn` VARCHAR(20) DEFAULT NULL;
END IF;
小开

This below worked for me:

    SELECT count(*)
INTO @exist
FROM information_schema.columns
WHERE table_schema = 'mydatabase'
and COLUMN_NAME = 'mycolumn'
AND table_name = 'mytable' LIMIT 1;


set @query = IF(@exist <= 0, 'ALTER TABLE mydatabase.`mytable`  ADD COLUMN `mycolumn` MEDIUMTEXT NULL',
'select \'Column Exists\' status');


prepare stmt from @query;


EXECUTE stmt;

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