How Do I Declare, Use, and Deallocate Variables in SQLite?

Simulating Variables in SQLite Using Temporary Tables

SQLite lacks native variable support, but we can effectively mimic variable behavior using temporary in-memory tables—a robust method even for extensive projects.

Creating a Variable

First, create a temporary table to hold variable names and their values:

<code class="language-sql">CREATE TEMP TABLE _Variables (
  Name TEXT PRIMARY KEY,
  RealValue REAL,
  IntegerValue INTEGER,
  BlobValue BLOB,
  TextValue TEXT
);

INSERT INTO _Variables (Name) VALUES ('MyVariable');</code>

This establishes _Variables, a temporary table storing variable names and their values across various data types.

Assigning a Value

Assign values based on their data type:

<code class="language-sql">UPDATE _Variables SET IntegerValue = 10 WHERE Name = 'MyVariable';</code>

Utilizing a Variable

Retrieve the variable's value within expressions:

<code class="language-sql">SELECT ..., (SELECT COALESCE(RealValue, IntegerValue, BlobValue, TextValue) FROM _Variables WHERE Name = 'MyVariable' LIMIT 1), ...</code>

COALESCE intelligently selects the appropriate value based on its data type.

Removing a Variable

Clean up after use:

<code class="language-sql">DROP TABLE _Variables;</code>

Alternatively, temporary tables are automatically dropped when a transaction concludes with END;.

The above is the detailed content of How Do I Declare, Use, and Deallocate Variables in SQLite?. For more information, please follow other related articles on the PHP Chinese website!