SQLite PRAGMA statements are special commands that provide control over various aspects of the SQLite database engine. PRAGMA, in the context of SQLite, stands for “PRogmA” and is used to query or modify the behavior of the SQLite database system. These statements are often used for administrative purposes, fine-tuning the database engine, or obtaining information about the database environment.
Here are some common uses of SQLite PRAGMA statements:
Setting Journal Mode:
PRAGMA journal_mode = WAL;
This sets the journal mode to Write-Ahead Logging (WAL), which can provide better write performance compared to the default rollback journal mode.
Setting Synchronous Mode:
PRAGMA synchronous = OFF;
This changes the synchronous mode to OFF, which can improve write performance at the cost of increased risk of data loss in the event of a crash.
Checking Foreign Key Support:
This PRAGMA is used to check whether foreign key constraints are enabled or disabled.
Checking Auto-Vacuum Mode:
This PRAGMA returns the current auto-vacuum mode, which determines how the database file is managed to reduce fragmentation.
Checking and Setting Cache Size:
PRAGMA cache_size; PRAGMA cache_size = 5000;
The first statement retrieves the current cache size, while the second statement sets the cache size to 5000 pages.
Checking and Setting Page Size:
PRAGMA page_size; PRAGMA page_size = 4096;
The first statement retrieves the current page size, while the second statement sets the page size to 4096 bytes.
Checking and Setting Temp Store Directory:
PRAGMA temp_store_directory; PRAGMA temp_store_directory = '/path/to/temp/directory';
The first statement retrieves the current temporary storage directory, while the second statement sets a new temporary storage directory.
Describe table structure:
This information is valuable when you need to understand the structure of a table(describe table), especially when working with dynamic queries or when generating reports based on the database schema. The PRAGMA table_info command provides a quick and convenient way to obtain such details about a specific table in SQLite.
These are just a few examples of the many PRAGMA statements available in SQLite. They provide a way to customize the behavior of the database engine to suit specific requirements or to obtain information about the current database settings. It’s important to note that PRAGMA statements are specific to SQLite and may not be supported in other database systems.