The syntax to drop a unique constraint from a table in SQLite is: PRAGMA foreign_keys=off Instead, you must create a new table with the unique constraint removed and copy the data into this new table. In SQLite, you can not use the ALTER TABLE statement to drop a unique constraint. You can drop the old_productstable once you have verified that your products table and data are as expected. The original table will still exist in the database called old_products. In this example, we've created a unique constraint on the products table called product_name_unique which consists of the product_name column. INSERT INTO products SELECT * FROM old_products We could run the following commands: PRAGMA foreign_keys=off ĪLTER TABLE products RENAME TO old_products ĬONSTRAINT product_name_unique UNIQUE (product_name) ( product_id INTEGER PRIMARY KEY AUTOINCREMENT,Īnd we wanted to add a unique constraint to the products table that consists of the product_name. So say, we already have a products table with the following definition: CREATE TABLE products Let's look at an example of how to add a unique constraint to an existing table in SQLite. uc_col_n The columns that make up the unique constraint. constraint_name The name of the unique constraint. It will be left behind after you have created the new table with the unique constraint added. old_table The name of the original table. This is the table that you wish to add a unique constraint to. PRAGMA foreign_keys=on table_name The name of the table to modify. INSERT INTO table_name SELECT * FROM old_table The syntax to add a unique constraint to a table in SQLite is: PRAGMA foreign_keys=off ĪLTER TABLE table_name RENAME TO old_table Instead, you must create a new table with the unique constraint and copy the data into this new table. If your table already exists and you wish to add a unique constraint later, you can not use the ALTER TABLE statement to add the unique constraint. It consists of the last_name and first_name fields. In this example, we've created a unique constraint on the employees table called name_unique. ( employee_id INTEGER PRIMARY KEY AUTOINCREMENT,ĬONSTRAINT name_unique UNIQUE (last_name, first_name) Let's look at an example of how to create a unique constraint in SQLite. column1, column2 The columns that you wish to create in the table. ) table_name The name of the table that you wish to create. The syntax for creating a unique constraint using a CREATE TABLE statement in SQLite is: CREATE TABLE table_nameĬONSTRAINT constraint_name UNIQUE (uc_col1, uc_col2. There is also a way to combine steps 2 and 3 into a single SQL command that creates the table and populates its data in a single step.A unique constraint can be created when you execute a CREATE TABLE statement in SQLite. But you can also send the commands from Xojo by using the Database.SQLExecute method. Typically you will run the above commands using your favorite SQL tool. In this case you would create the new table without the column you want to delete and then don't copy that column's data over to it. You can also use the above steps to remove a column from a table as SQLite has no ability to do that. Keep in mind that you will also need to recreate any indexes, viewers or triggers on the new table as well. With these four steps you can manually change any SQLite table.
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