GitHub: _posts/-mysql-drop-column-if-exists. If exists (select * from information_lumns where table_name = 'table1' and column_name = 'column2') thenĪlter table table1 drop column `column2` Īlter table table1 add column `column1` varchar(255) NULL Īlter table table1 add column `column2` varchar(255) NULL If exists (select * from information_lumns where table_name = 'table1' and column_name = 'column1') thenĪlter table table1 drop column `column1` However, because you need an IF statement, it will need to be a stored procedure. 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. MySQL has a built-in modifier for this.įor some reason, the same facility does not exist in MySQL for dropping a column if it exists. step3: alter table buyers drop constraint UQbuyers1299A860D9793F2E alter table buyers drop column empid. The tool then generates the appropriate alter table drop column SQL command. To drop several columns, specify the tableName as an attribute, and then specify a set of nested tags.To drop a single column, use the simple form of this element where the tableName and columnName are specified as attribute s. You said you drop condition field but MySQl reported syntax to use near condition hello varchar(255).Maybe theres part of your code that accidentally add this hello varchar(255) line to your SQL. The drop column function allows the user to select a column to drop from the table. The dropColumn Change Type drops existing columns. In case of more than one INDEX applied on a column. INDEX names are usually same as column names. First you need to know the exact name of the INDEX (Unique key in this case) to delete or update it. step 1: exec sphelpindex buyers, see the image file. Your SQL ALTER TABLE command looks different than what MySQL receive. ALTER TABLE tblquizattemptmaster DROP INDEX indexname ALTER TABLE tblquizattemptmaster DROP INDEX PRIMARY ALTER TABLE Syntax. The most common operation you will want to do is to drop a table or column, but only if it exists. my table name is buyers which has a unique constraint column empid now iam going to drop the empid. You could add yet another schema update to fix this, or if your script was idempotent, you could simply modify the original script and run it again. You actually want a column to be varchar(255), not a varchar(50). Why might you want to code idempotent schema updates? Say your initial version of the schema update got it slightly wrong. If the column that you want to delete has a CHECK constraint, you must delete the constraint first before removing the column. Second, specify the name of the column that you want to delete. you should be able to run the script more than once, no run should error out, and the end result should be the same as when you ran it the first time. To do this, you use the ALTER TABLE DROP COLUMN statement as follows: First, specify the name of the table from which you want to delete the column. When updating a database schema, it's very useful to make your SQL scripts idempotent. Idempotence describes the property of operations in mathematics and computer science that means that multiple applications of the operation do not change the result.
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