Migrate install rewriting to new rewriters

pg4wp/rewriters/ShowVariablesSQLRewriter.php

@@ -0,0 +1,41 @@
+<?php
+
+class ShowVariablesSQLRewriter extends AbstractSQLRewriter
+{
+    public function rewrite(): string
+    {
+        $sql = $this->original();
+        $table = $this->extractVariableName($sql);
+        return $this->generatePostgres($sql, $variableName);
+    }
+
+    /**
+     * Extracts table name from a "SHOW FULL COLUMNS" SQL statement.
+     *
+     * @param string $sql The SQL statement
+     * @return string|null The table name if found, or null otherwise
+     */
+    protected function extractVariableName($sql) {
+        $pattern = "/SHOW VARIABLES LIKE ['\"`]?([^'\"`]+)['\"`]?/i";
+        if (preg_match($pattern, $sql, $matches)) {
+            return $matches[1];
+        }
+        return null;
+    }
+
+    /**
+     * Generates a PostgreSQL-compatible SQL query to mimic MySQL's "SHOW VARIABLES".
+     *
+     * @param string $tableName The table name
+     * @return string The generated SQL query
+     */
+    function generatePostgres($sql, $variableName) {
+        if ($variableName == "sql_mode") {
+            // Act like MySQL default configuration, where sql_mode is ""
+            return "SELECT '$variableName' AS \"Variable_name\", '' AS \"Value\";";
+        }
+
+        // return untransformed sql
+        return $sql;
+    }
+}