The Operations system is also fully extensible. So symbols can be imported safely from the alembic.op namespace. With individual proxies for each method on Operations, To the script via the alembic.op datamember, which isĪ proxy to an actual instance of Operations.Ĭurrently, alembic.op is a real Python module, populated When migration scripts are run, this object is made available Within the upgrade() and downgrade() functions, as well asĪll directives exist as methods on a class called Operations. The directives here are used within user-defined migration files, You can drop the old_suppliers table once you have verified that your suppliers table and data are as expected.This file provides documentation on Alembic migration directives. The original table will still exist in the database called old_suppliers. In this example, we've dropped the unique constraint on the existing suppliers table. INSERT INTO suppliers SELECT * FROM old_suppliers We could run the following commands: PRAGMA foreign_keys=off ĪLTER TABLE suppliers RENAME TO old_suppliers ( supplier_id INTEGER PRIMARY KEY AUTOINCREMENT,ĬONSTRAINT supplier_name_unique UNIQUE (supplier_name)Īnd we wanted to drop the unique constraint from the suppliers table. So say, we already have a suppliers table with the following definition: CREATE TABLE suppliers Let's look at an example of how to remove a unique constraint from an existing table in SQLite. It will be left behind after you have created the new table with the unique constraint removed. old_table The name of the original table. This is the table that you wish to remove the unique constraint from. PRAGMA foreign_keys=on table_name The name of the table to modify. 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. This is the table that you wish to add a unique constraint to. 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. A unique constraint can be created when you execute a CREATE TABLE statement in SQLite.
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