My code, which doesnt work. MYSQL How to alter table if column doesnt exist. ALTER TABLE child ADD FOREIGN KEY my_fk (parent_id) REFERENCES parent(ID); MySQL has the ability to enforce a record that exists on a parent table when you are adding/modifying data or validate that a record doesn’t exist when you are deleting data from your child table, leaving your database inconsistent. Viewed 3k times 1. Each index will be assigned a name (perhaps column_to_index,column_to_index_1). This is called Foreign Key. ALTER TABLE test ADD COLUMN IF NOT EXISTS column_a VARCHAR(255);. I am using SQL which doesnt support INFORMATION_SCHEMA.COLUMNS. DROP TABLE IF EXISTS candidate; CREATE TABLE candidate... For some reason, the same facility does not exist in MySQL for dropping a column if it exists. Check for an existing column, if it exists we dont do anything, else we create the column. This statement drops a trigger. add column to mysql table if it does not exist, Actually exists now for Maria DB 10.219. ALTER TABLE Report ADD IF NOT EXISTS LastName CHAR(25); this works. Active 6 years, 3 months ago. ; column_definition– specify the datatype, maximum size, and column constraint of the new column; FIRST | AFTER column_name specify the position of the new column in the table. –> Previously with ALTER statement, to DROP any item you had to check the existence of it with a separate IF EXISTS() statement, and then DROP it within the IF condition, like: IF EXISTS (select * from INFORMATION_SCHEMA.COLUMNS WHERE COLUMN_NAME = 'vCustomerName') BEGIN ALTER TABLE Sales.SalesOrder_json DROP COLUMN vCustomerName; END GO DROP TRIGGER [IF EXISTS] [schema_name.]trigger_name. If you try to create a table and the table name already exist then MySQL will give a warning message. The schema (database) name is optional. ALTER TABLE table_name ADD INDEX (column_to_index); ALTER TABLE table_name ADD INDEX (column_to_index); This will definitely create two indexes without checking. ALTER TABLE Task ADD Name varchar(200); thats the code that causes the problem because its trying to add an existing column. Of course, you are trying to avoid that. Here, we are creating a table that already exist − mysql> CREATE TABLE IF NOT EXISTS DemoTable ( CustomerId int, CustomerName varchar(30), CustomerAge int ); Query OK, 0 rows affected, 1 warning (0.05 sec) Ask Question Asked 6 years, 3 months ago. In this syntax: table_name – specify the name of the table that you want to add a new column or columns after the ALTER TABLE keywords. MySQL NDB Cluster 8.0 supports setting NDB_TABLE options for controlling a table's partition balance (fragment count type), read-from-any-replica capability, full replication, or any combination of these, as part of the table comment for an ALTER TABLE statement in the same manner as for CREATE TABLE, as shown in this example: Description: When dropping columns (or indexes), it should be possible to use the if exists clause.How to repeat: No way to repeat. The DROP DATABASE IF EXISTS, DROP TABLE IF EXISTS, and DROP VIEW IF EXISTS statements are always replicated, even if the database, table, or view to be dropped does not exist on the source. If the schema is omitted, the trigger is dropped from the default schema. But you can fake it, at least in MySQL 5 or later, by querying the database meta-data do see if the column exists, and drop it if it does. Check INFORMATION_SCHEMA first ; new_column_name – specify the name of the new column. DROP TRIGGER requires the TRIGGER privilege for the table associated with the trigger. Let us verify the concept. This is to ensure that the object to be dropped no longer exists on either the source or the replica, once the replica has caught up with the source. :-) Suggested fix: create table t1 (Number int not null); alter table t1 add column t2 int not null; alter table t1 drop column t2; <---- OK - this works so far.
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