If a table has the primary key that consists of one column, and that column is defined as INTEGER then this primary key column becomes an alias for the rowid column. Tables that have rowid columns are called rowid tables. The rowid column is a key that uniquely identifies the rows in the table. When you create a table without specifying the WITHOUT ROWID option, SQLite adds an implicit column called rowid that stores 64-bit signed integer. However, to make the current version of SQLite compatible with the earlier version, SQLite allows the primary key column to contain NULL values. It means that the primary key column has an implicit NOT NULL constraint. In SQL standard, the primary key column must not contain NULL values.
#Sqlite data types code
) Code language: SQL (Structured Query Language) ( sql ) Second, in case primary key consists of two or more columns, you use the PRIMARY KEY table constraint to define the primary as shown in the following statement. SQLite allows you to define primary key in two ways:įirst, if the primary key has only one column, you use the PRIMARY KEY column constraint to define the primary key as follows: CREATE TABLE table_name( Each table has one and only one primary key. Introduction to SQLite primary keyĪ primary key is a column or group of columns used to identify the uniqueness of rows in a table.
#Sqlite data types how to
If the declared type for a column contains any of the strings "REAL", "FLOA", or "DOUB" then the column has REAL affinity.Summary: in this tutorial, you will learn how to use SQLite PRIMARY KEY constraint to define a primary key for a table. If the declared type for a column contains the string "BLOB" or if no type is specified then the column has affinity NONE. Notice that the type VARCHAR contains the string "CHAR" and is thus assigned TEXT affinity. If the declared type of the column contains any of the strings "CHAR", "CLOB", or "TEXT" then that column has TEXT affinity. If the declared type contains the string "INT" then it is assigned INTEGER affinity. The affinity of a column is determined by the declared type of the column, according to the following rules in the order shown: The preferred storage class for a column is called its "affinity".Įach column in an SQLite 3 database is assigned one of the following type affinities: It is just that some columns, given the choice, will prefer to use one storage class over another. Any column can still store any type of data.
The important idea here is that the type is recommended, not required. The type affinity of a column is the recommended type for data stored in that column. In order to maximize compatibility between SQLite and other database engines, SQLite supports the concept of "type affinity" on columns. The value is a blob of data, stored exactly as it was input. The value is a text string, stored using the database encoding (UTF-8, UTF-16BE or UTF-16LE).īLOB. The value is a floating point value, stored as an 8-byte IEEE floating point number. The value is a signed integer, stored in 1, 2, 3, 4, 6, or 8 bytes depending on the magnitude of the value. However, the dynamic typing in SQLite allows it to do things which are not possible in traditional rigidly typed databases.Įach value stored in an SQLite database (or manipulated by the database engine) has one of the following storage classes: The dynamic type system of SQLite is backwards compatible with the more common static type systems of other database engines in the sense that SQL statement that work on statically typed databases should work the same way in SQLite. In SQLite, the datatype of a value is associated with the value itself, not with its container. SQLite uses a general dynamic type system.
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