Add SQLite database compatibility for all queries

[Copilot]

Plugin queries use MySQL-specific syntax that fails on WordPress SQLite installations. This adds cross-database compatibility for SQLite Database Integration plugin support.

New Helper Functions

• edac_is_sqlite() - Detects SQLite via DB_ENGINE constant, SQLITE_DB_DROPIN_VERSION, or driver class inspection
• edac_table_exists() - Uses sqlite_master for SQLite, SHOW TABLES LIKE for MySQL

Query Compatibility Fixes

• class-update-database.php - Replaced SHOW TABLES LIKE with edac_table_exists()
• class-purge-post-data.php - MySQL multi-table DELETE (DELETE T1,T2 FROM ... JOIN) replaced with separate DELETE statements for SQLite
• class-issues-query.php - MySQL COUNT(DISTINCT col1, col2) replaced with concatenation for SQLite

// SQLite-compatible distinct count
if ( edac_is_sqlite() ) {
    $this->query['select'] = "SELECT COUNT( DISTINCT rule || '|' || object ) ";
} else {
    $this->query['select'] = 'SELECT COUNT( DISTINCT rule, object ) ';
}

Tests

Added SqliteCompatibilityTest.php covering the new helper functions.

Original prompt

Make the queries in this plugin all support sql lite

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[coderabbitai]

Important

Review skipped

Bot user detected.

To trigger a single review, invoke the @coderabbitai review command.

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}