DELETING COLUMN IN DB SQLITE CODE

A generated column cannot reference itself, either directly or indirectly.However, it possible to use the ALTER TABLE ADD COLUMN statement to add a VIRTUAL column. It’s NOT possible to use the ALTER TABLE ADD COLUMN statement to add a STORED column.If a table has a generated column, it must have a least one generated columns.A generated column cannot be used as a part of a PRIMARY KEY.A generated column cannot have a default value.SQLite places the following constraints on generated columns: A generated column can reference other columns including other generated columns within the same table as long as it does not reference itself.A generated column can be a part of one or more indexes.A generated column can have NOT NULL, CHECK, UNIQUE, and FOREIGN KEY constraints.SQLite will convert the value from the expression to that data type using the same affinity rules as for regular columns.

A generated column can have a datatype.

Generated columns have the following features: Result: name price discount tax net_priceĪs you can see clearly from the output, the value of the net_price column is calculated based on the values of the price, discount, and tax columns.

DELETING COLUMN IN DB SQLITE CODE

Third, query data from the products table: SELECT * FROM products Code language: SQL (Structured Query Language) ( sql ) VALUES( 'ABC Widget', 100, 0.05, 0.07) Code language: SQL (Structured Query Language) ( sql ) Note that it doesn’t supply values to the net_price column: INSERT INTO products( name, price, discount, tax) Second, insert a new row into the products table. In the products table, the net_price is a generated column whose value derived from the price, discount, and tax columns.īecause we didn’t specify VIRTUAL or STORED for the net_price column, the net_price column uses VIRTUAL by default. ) Code language: SQL (Structured Query Language) ( sql ) Net_price REAL GENERATED ALWAYS AS (price * ( 1-discount) * ( 1+tax)) SQLite generated column exampleįirst, create a table called products by using the following CREATE TABLE statement: CREATE TABLE products( In practice, you use the STORED option when you want to optimize for reading and the VIRTUAL option when you want to optimize for writing. SQLite uses the VIRTUAL by default when you don’t explicitly specify VIRTUAL or STORED in the generated column declaration.

SQLite updates the values of the STORED generated column when you write to the database. In other words, the STORED generated column takes up spaces in the database file. In case a generated column is STORED, SQLite stores the values of the column physically. Instead, when you read values from the generated column, SQLite computes these values based on the expression specified in the column declaration. If a generated column is VIRTUAL, SQLite doesn’t store the values of the column physically. Therefore, you can make it shorter as follows: column_name data_type AS expression Code language: SQL (Structured Query Language) ( sql )Ī generated column can be either VIRTUAL or STORED. The GENERATED ALWAYS keywords are optional. The expression typically involves columns of the same row within the same table.

In this syntax, you specify the expression that computes values for the column_name after the GENERATED ALWAYS keywords. Code language: SQL (Structured Query Language) ( sql ) To define a generated column, you use the GENERATED ALWAYS column constraint syntax as follows: column_name data_type Generated columns are also known as computed columns. SQLite introduced the generated columns since version 3.31.0.īy definition, generated columns are the columns of a table whose values are derived from an expression that involves other columns of the same table. Summary: in this tutorial, you will learn about the SQLite generated columns.

Deleting column in db sqlite