![]() CREATE TABLE countries (īecause the primary key of the countries table has only one column, we defined the primary key using PRIMARY KEY column constraint. The following statement creates a table named countries which has country_id column as the primary key. ![]() ![]() ) Code language: SQL (Structured Query Language) ( sql ) Creating SQLite primary key examples ![]() It is faster than using a primary key which is not an alias of the rowid.Īnother important note is that if you declare a column with the INTEGER type and PRIMARY KEY DESC clause, this column will not become an alias for the rowid column: CREATE TABLE table( Notice that if you assign another integer type such as BIGINT and UNSIGNED INT to the primary key column, this column will not be an alias for the rowid column.īecause the rowid table organizes its data as a B-tree, querying and sorting data of a rowid table are very fast. 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. ) 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. If the table is to contain bulk-loaded data (that is, something else is recording the data feed and you are merely loading a bunch of data for analysis) then you should order your index to be most useful for how you will normally be accessing and querying the data since you will only be loading the data once, not continuously.Summary: in this tutorial, you will learn how to use SQLite PRIMARY KEY constraint to define a primary key for a table. So to save time I will answer those next questions now. If you put the wxsite_id first then each second when a new sample arrives you will have to rebalance the index to perform the insert because the inserts will not be in-order, and you will be wondering why there is (1) tremendous I/O occurring when you are only adding itty-bitty records (2) why sometimes it takes 1000 times longer to insert a record than it ususally does. That is, for each sampdate you will get multiple samptime and for each of those multiple wxsite_id and for each of those multiple wxparam_name. The order should be from most stable to least stable (ie, in increasing order of change). ![]() If this is for collection of realtime data I would consider rearranging the order or your primary key since it is in the wrong order and will result in excessive continuous rebalancing of the index. As such it follows the ()'s delimiting the contents of the table. The keywords WITHOUT ROWID to designate that a table does not have a rowid is a qualifier of the table, not of the contents in the table. The type of the constraint is 'primary key' so if you want to have that constraint named 'primary' then you must use the syntax constraint primary primary key (.). The keyword "constraint" is used to give a name to a constraint and so the construction "constraint primary key" is attempting to create a constraint named 'primary' with a next keyword (type) of key. Note that the columns in a primary key must be constrained NOT NULL for a "without rowid" table. Primary key (wxsite_id, sampdate, samptime, wxparam_name), Wxparam_name TEXT not null references WeaatherParams(wxparam_name) Wxsite_id INT not null references WeatherSites(wxsite_id) ![]()
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