diff --git a/lib/Models/AccountEntity.php b/lib/Models/AccountEntity.php
index 5d3f6db..505af0b 100644
--- a/lib/Models/AccountEntity.php
+++ b/lib/Models/AccountEntity.php
@@ -6,6 +6,11 @@
 
 readonly class AccountEntity {
 	public const TABLE = 'stalwart_accounts';
+	public const COL_ID = 'uid';
+	public const COL_TYPE = 'type';
+	public const COL_DISPLAY = 'display_name';
+	public const COL_PASSWORD = 'password';
+	public const COL_QUOTA = 'quota';
 
 	public function __construct(
 		public string       $uid,
@@ -21,31 +26,31 @@ public static function parse(ConfigEntity $conf, mixed $value): self {
 		if (!is_array($value)) {
 			throw new ValueError('value must be an array');
 		}
-		if (!is_string($value['uid'])) {
+		if (!is_string($value[self::COL_ID])) {
 			throw new ValueError('uid must be a string');
 		}
-		if ($value['cid'] !== $conf->cid) {
+		if ($conf->cid !== $value[ConfigEntity::COL_ID]) {
 			throw new ValueError('cid must be an integer');
 		}
-		if (!is_string($value['display_name'])) {
+		if (!is_string($value[self::COL_DISPLAY])) {
 			throw new ValueError('display_name must be a string');
 		}
-		if (!is_string($value['password'])) {
+		if (!is_string($value[self::COL_PASSWORD])) {
 			throw new ValueError('password must be a string');
 		}
-		if (!is_string($value['type'])) {
+		if (!is_string($value[self::COL_TYPE])) {
 			throw new ValueError('type must be a string');
 		}
-		if (!is_int($value['quota'])) {
+		if (!is_int($value[self::COL_QUOTA])) {
 			throw new ValueError('quota must be an integer');
 		}
 		return new self(
-			$value['uid'],
+			$value[self::COL_ID],
 			$conf,
-			$value['display_name'],
-			$value['password'],
-			AccountType::from($value['type']),
-			$value['quota']
+			$value[self::COL_DISPLAY],
+			$value[self::COL_PASSWORD],
+			AccountType::from($value[self::COL_TYPE]),
+			$value[self::COL_QUOTA],
 		);
 	}
 }
diff --git a/lib/Models/ConfigEntity.php b/lib/Models/ConfigEntity.php
index f058c43..d3bf0bc 100644
--- a/lib/Models/ConfigEntity.php
+++ b/lib/Models/ConfigEntity.php
@@ -9,6 +9,11 @@
 /** @psalm-import-type StalwartServerConfig from ResponseDefinitions */
 readonly class ConfigEntity implements JsonSerializable {
 	public const TABLE = 'stalwart_configs';
+	public const COL_ID = 'cid';
+	public const COL_ENDPOINT = 'endpoint';
+	public const COL_USERNAME = 'username';
+	public const COL_PASSWORD = 'password';
+	public const COL_HEALTH = 'health';
 	private const URL_PATTERN = '/^https?:\\/\\/([a-z0-9-]+\\.)*[a-z0-9-]+(:\\d{1,5})?\\/api$/';
 
 
@@ -29,27 +34,27 @@ public static function parse(mixed $value): ConfigEntity {
 		if (!is_array($value)) {
 			throw new ValueError('value must be an array');
 		}
-		if (!is_string($value['cid'])) {
+		if (!is_string($value[self::COL_ID])) {
 			throw new ValueError('cid must be a string');
 		}
-		if (!is_string($value['endpoint'])) {
+		if (!is_string($value[self::COL_ENDPOINT])) {
 			throw new ValueError('endpoint must be a string');
 		}
-		if (!is_string($value['username'])) {
+		if (!is_string($value[self::COL_USERNAME])) {
 			throw new ValueError('username must be a string');
 		}
-		if (!is_string($value['password'])) {
+		if (!is_string($value[self::COL_PASSWORD])) {
 			throw new ValueError('password must be a string');
 		}
-		if (!is_string($value['health'])) {
+		if (!is_string($value[self::COL_HEALTH])) {
 			throw new ValueError('health must be a string');
 		}
 		return new self(
-			$value['cid'],
-			$value['endpoint'],
-			$value['username'],
-			$value['password'],
-			ServerStatus::from($value['health'])
+			$value[self::COL_ID],
+			$value[self::COL_ENDPOINT],
+			$value[self::COL_USERNAME],
+			$value[self::COL_PASSWORD],
+			ServerStatus::from($value[self::COL_HEALTH]),
 		);
 	}
 
diff --git a/lib/Models/EmailEntity.php b/lib/Models/EmailEntity.php
index b18b7ac..c62fa67 100644
--- a/lib/Models/EmailEntity.php
+++ b/lib/Models/EmailEntity.php
@@ -6,6 +6,8 @@
 
 readonly class EmailEntity {
 	public const TABLE = 'stalwart_emails';
+	public const COL_EMAIL = 'email';
+	public const COL_TYPE = 'type';
 
 	public function __construct(
 		public AccountEntity $account,
diff --git a/lib/Services/ISqlService.php b/lib/Services/ISqlService.php
index 3596ae3..3648f3a 100644
--- a/lib/Services/ISqlService.php
+++ b/lib/Services/ISqlService.php
@@ -2,9 +2,149 @@
 
 namespace OCA\Stalwart\Services;
 
+use Exception;
+use OCA\Stalwart\Models\AccountEntity;
+use OCA\Stalwart\Models\ConfigEntity;
+use OCA\Stalwart\Models\EmailEntity;
+use OCA\Stalwart\Models\EmailType;
 use OCP\IConfig;
 
-interface ISqlService {
-	public function __construct(IConfig $config);
-	public function getStalwartConfig(string $cid): string;
+abstract readonly class ISqlService {
+	/**
+	 * @throws Exception
+	 */
+	protected function queryName(string $cid): string {
+		if (preg_match('/\W/', $cid)) {
+			throw new Exception('The configuration ID is invalid, only word characters allowed to prevent SQL injection');
+		}
+		$table = $this->dbNcPrefix . AccountEntity::TABLE;
+		$colId = AccountEntity::COL_ID;
+		$colType = AccountEntity::COL_TYPE;
+		$colDisplay = AccountEntity::COL_DISPLAY;
+		$colPassword = AccountEntity::COL_PASSWORD;
+		$colQuota = AccountEntity::COL_QUOTA;
+		$colConfig = ConfigEntity::COL_ID;
+		$param = $this->dbParam;
+		// SELECT name, type, secret, description, quota FROM accounts WHERE name = ? AND active = true
+		// SELECT name, type, secret, description, quota FROM accounts WHERE name = $1 AND active = true
+		return "SELECT $colId, $colType, $colDisplay, $colPassword, $colQuota FROM $table WHERE $colConfig = '$cid' AND $colId = $param";
+	}
+
+	// SELECT member_of FROM group_members WHERE name = ?
+	// SELECT member_of FROM group_members WHERE name = $1
+	protected function queryMembers(): string {
+		$table = $this->dbNcPrefix . AccountEntity::TABLE;
+		$colId = AccountEntity::COL_ID;
+		$colMember = AccountEntity::COL_ID;
+		$param = $this->dbParam;
+		return "SELECT $colMember FROM $table WHERE $colId = $param LIMIT 0";
+	}
+
+	protected function queryRecipients(): string {
+		$table = $this->dbNcPrefix . AccountEntity::TABLE;
+		$colId = AccountEntity::COL_ID;
+		$colEmail = EmailEntity::COL_EMAIL;
+		$param = $this->dbParam;
+		// SELECT name FROM emails WHERE address = ? ORDER BY name ASC
+		// SELECT name FROM emails WHERE address = $1 ORDER BY name ASC
+		return "SELECT $colId FROM $table WHERE  $colEmail = $param ORDER BY $colId ASC";
+	}
+
+	protected function queryEmails(): string {
+		$table = $this->dbNcPrefix . EmailEntity::TABLE;
+		$colId = AccountEntity::COL_ID;
+		$colEmail = EmailEntity::COL_EMAIL;
+		$colType = EmailEntity::COL_TYPE;
+		$typeList = EmailType::List->value;
+		$param = $this->dbParam;
+		// SELECT address FROM emails WHERE name = ? AND type != 'list' ORDER BY type DESC, address ASC
+		// SELECT address FROM emails WHERE name = $1 AND type != 'list' ORDER BY type DESC, address ASC
+		return "SELECT $colEmail FROM $table WHERE $colId = $param AND $colType != '$typeList' ORDER BY $colType DESC, $colEmail ASC";
+	}
+
+	protected function queryVerify(): string {
+		$table = $this->dbNcPrefix . EmailEntity::TABLE;
+		$colEmail = EmailEntity::COL_EMAIL;
+		$colType = EmailEntity::COL_TYPE;
+		$typePrimary = EmailType::Primary->value;
+		$concat = $this->concatVerify;
+		// SELECT address FROM emails WHERE address LIKE CONCAT('%', ?, '%') AND type = 'primary' ORDER BY address LIMIT 5
+		// SELECT address FROM emails WHERE address LIKE '%' || $1 || '%' AND type = 'primary' ORDER BY address LIMIT 5
+		return "SELECT $colEmail FROM $table WHERE $colEmail LIKE $concat AND $colType = '$typePrimary' ORDER BY $colEmail LIMIT 5";
+	}
+
+	protected function queryExpand(): string {
+		$table = $this->dbNcPrefix . EmailEntity::TABLE;
+		$colId = AccountEntity::COL_ID;
+		$colEmail = EmailEntity::COL_EMAIL;
+		$colType = EmailEntity::COL_TYPE;
+		$typePrimary = EmailType::Primary->value;
+		$typeList = EmailType::List->value;
+		$param = $this->dbParam;
+		// SELECT p.address FROM emails AS p JOIN emails AS l ON p.name = l.name WHERE p.type = 'primary' AND l.address = ? AND l.type = 'list' ORDER BY p.address LIMIT 50
+		// SELECT p.address FROM emails AS p JOIN emails AS l ON p.name = l.name WHERE p.type = 'primary' AND l.address = $1 AND l.type = 'list' ORDER BY p.address LIMIT 50
+		return "SELECT p.$colEmail FROM $table AS p JOIN $table AS l USING ($colId) WHERE p.$colType = '$typePrimary' AND l.$colType = '$typeList' AND l.$colEmail = $param ORDER BY p.$colEmail LIMIT 50";
+	}
+
+	protected function queryDomains(): string {
+		$table = $this->dbNcPrefix . EmailEntity::TABLE;
+		$colEmail = EmailEntity::COL_EMAIL;
+		$concat = $this->concatDomains;
+		// SELECT 1 FROM emails WHERE address LIKE CONCAT('%@', ?) LIMIT 1
+		// SELECT 1 FROM emails WHERE address LIKE '%@' || $1 LIMIT 1
+		return "SELECT 1 FROM $table WHERE $colEmail LIKE $concat LIMIT 1";
+	}
+
+	protected string $dbHost;
+	protected int $dbPort;
+	protected string $dbName;
+	protected string $dbUser;
+	protected string $dbPassword;
+	private string $dbNcPrefix;
+	private string $dbParam;
+	private string $concatVerify;
+	private string $concatDomains;
+
+	/**
+	 * @throws Exception
+	 */
+	public function __construct(IConfig $config) {
+		$host = $config->getSystemValueString('dbhost');
+		if ($host === '') {
+			throw new Exception('The database host looks empty but it should be set');
+		}
+		$this->dbHost = $host;
+
+		$name = $config->getSystemValueString('dbname');
+		if ($name === '') {
+			throw new Exception('The database name looks empty but it should be set');
+		}
+		$this->dbName = $name;
+
+		$prefix = $config->getSystemValueString('dbtableprefix');
+		if (preg_match('/\W/', $prefix)) {
+			throw new Exception('The database table prefix is invalid, only word characters allowed to prevent SQL injection');
+		}
+		$this->dbNcPrefix = $prefix;
+
+		$port = $config->getSystemValueInt('dbport');
+		$type = $config->getSystemValueString('dbtype');
+		if ($type == 'mysql') {
+			$this->dbPort = $port === 0 ? 3306 : $port;
+			$this->dbParam = '?';
+			$this->concatVerify = "CONCAT('%', ?, '%')";
+			$this->concatDomains = "CONCAT('%@', ?)";
+		} elseif ($type == 'pgsql') {
+			$this->dbPort = $port === 0 ? 5432 : $port;
+			$this->dbParam = '$1';
+			$this->concatVerify = "'%' || $1 || '%'";
+			$this->concatDomains = "'%@' || $1";
+		} else {
+			throw new Exception('This app only supports MySQL and PostgreSQL');
+		}
+		$this->dbUser = $config->getSystemValueString('dbuser');
+		$this->dbPassword = $config->getSystemValueString('dbpassword');
+	}
+
+	abstract public function getStalwartConfig(string $cid): string;
 }
diff --git a/lib/Services/MysqlService.php b/lib/Services/MysqlService.php
index ec7051a..4c4704a 100644
--- a/lib/Services/MysqlService.php
+++ b/lib/Services/MysqlService.php
@@ -4,139 +4,49 @@
 
 use Exception;
 use OCA\Stalwart\Models\AccountEntity;
-use OCA\Stalwart\Models\EmailEntity;
-use OCP\IConfig;
 
-readonly class MysqlService implements ISqlService {
-	// SELECT name, type, secret, description, quota FROM accounts WHERE name = ? AND active = true
-	private const QUERY_NAME = <<<SQL
-SELECT uid, type, display_name, password, quota FROM oc_stalwart_accounts
-WHERE cid = ':cid' AND uid = ?
-SQL;
+readonly class MysqlService extends ISqlService {
 
-	// SELECT member_of FROM group_members WHERE name = ?
-	private const QUERY_MEMBERS = <<<SQL
-SELECT 'TODO'
-WHERE 'TODO' = ?
-LIMIT 1
-SQL;
-
-	// SELECT name FROM emails WHERE address = ? ORDER BY name ASC
-	private const QUERY_RECIPIENTS = <<<SQL
-SELECT uid FROM oc_stalwart_emails
-JOIN oc_stalwart_accounts USING (uid)
-WHERE cid = ':cid' AND email = ?
-ORDER BY uid
-SQL;
-	// SELECT address FROM emails WHERE name = ? AND type != 'list' ORDER BY type DESC, address ASC
-	private const QUERY_EMAILS = <<<SQL
-SELECT email FROM oc_stalwart_emails
-JOIN oc_stalwart_accounts USING (uid)
-WHERE cid = ':cid' AND uid = ? AND type != 'list'
-ORDER BY type DESC, email
-SQL;
-
-	// SELECT address FROM emails WHERE address LIKE CONCAT('%', ?, '%') AND type = 'primary' ORDER BY address LIMIT 5
-	private const QUERY_VERIFY = <<<SQL
-SELECT email FROM oc_stalwart_emails
-JOIN oc_stalwart_accounts USING (uid)
-WHERE cid = ':cid' AND email LIKE CONCAT('%', ?, '%') AND type = 'primary'
-SQL;
-
-	// SELECT p.address FROM emails AS p JOIN emails AS l ON p.name = l.name WHERE p.type = 'primary' AND l.address = ? AND l.type = 'list' ORDER BY p.address LIMIT 50
-	private const QUERY_EXPAND = <<<SQL
-SELECT p.email FROM oc_stalwart_emails AS p
-JOIN oc_stalwart_emails AS l USING (uid)
-JOIN oc_stalwart_accounts USING (uid)
-WHERE cid = :cid AND p.type = 'primary' AND l.email = ? AND l.type = 'alias'
-SQL;
-
-	// SELECT 1 FROM emails WHERE address LIKE CONCAT('%@', ?) LIMIT 1
-	private const QUERY_DOMAINS = <<<SQL
-SELECT 1 FROM oc_stalwart_emails
-WHERE cid = :cid AND email LIKE CONCAT('%@', ?)
-LIMIT 1
-SQL;
-
-	/**
-	 * @throws Exception
-	 */
-	public function __construct(
-		private IConfig $config,
-	) {
-	}
 
 	/**
 	 * @throws Exception
 	 */
 	public function getStalwartConfig(string $cid): string {
-		$dbType = $this->config->getSystemValueString('dbtype');
-		if ($dbType !== 'mysql') {
-			throw new Exception('This app only supports MySQL');
-		}
-		$dbHost = $this->config->getSystemValueString('dbhost');
-		if ($dbHost === '') {
-			throw new Exception('No database host configured');
-		}
-		$dbName = $this->config->getSystemValueString('dbname');
-		if ($dbName === '') {
-			throw new Exception('No database name configured');
-		}
-		$dbUser = $this->config->getSystemValueString('dbuser');
-		if ($dbUser === '') {
-			throw new Exception('No database user configured');
-		}
-		$dbPassword = $this->config->getSystemValueString('dbpassword');
-		if ($dbPassword === '') {
-			throw new Exception('No database password configured');
-		}
-		$dbTablePrefix = $this->config->getSystemValueString('dbtableprefix');
-		// to prevent SQL injection dbTablePrefix must match /^[a-zA-Z0-9_]*$/
-		if (!preg_match('/^\w+$/', $dbTablePrefix)) {
-			throw new Exception('Invalid database table prefix');
-		}
-		$dbPort = $this->config->getSystemValueInt('dbport');
-		if ($dbPort === 0) {
-			$dbPort = 3306;
-		}
-		$tableAccounts = $dbTablePrefix . AccountEntity::TABLE;
-		$tableEmail = $dbTablePrefix . EmailEntity::TABLE;
-
 		return json_encode([
 			[
-				'prefix' => 'directory.' . $cid,
+				'prefix' => "directory.$cid" ,
 				'type' => 'Clear',
 			],
 			[
-				'prefix' => 'store.' . $cid,
+				'prefix' => "store.$cid" ,
 				'type' => 'Clear',
 			],
 			[
 				'assert_empty' => false,
-				'prefix' => 'store.' . $cid,
+				'prefix' => "store.$cid" ,
 				'type' => 'Insert',
 				'values' => [
-					[ 'type', $dbType ],
-					[ 'host', $dbHost ],
-					[ 'port', strval($dbPort) ],
-					[ 'database', $dbName ],
-					[ 'user', $dbUser ],
-					[ 'password', $dbPassword ],
-					[ 'tls.enabled', 'false' ],
-					[ 'tls.allow-invalid-certs', 'false'],
-					[ 'pool.max-connections', '10' ],
-					[ 'pool.min-connections', '5' ],
-					[ 'timeout', '15s'],
-					[ 'compression', 'lz4'],
-					[ 'purge.frequency', '0 3 *'],
+					['type', 'mysql'],
+					['host', $this->dbHost],
+					['port', strval($this->dbPort)],
+					['database', $this->dbName],
+					['user', $this->dbUser],
+					['password', $this->dbPassword],
+					['tls.enabled', 'false'],
+					['tls.allow-invalid-certs', 'false'],
+					['pool.max-connections', '10'],
+					['pool.min-connections', '5'],
+					['timeout', '15s'],
+					['compression', 'lz4'],
+					['purge.frequency', '0 3 *'],
 					['read-from-replicas', 'true'],
-					['query.name', self::parseQuery(self::QUERY_NAME, $cid, $tableAccounts, $tableEmail)],
-					['query.members', self::parseQuery(self::QUERY_MEMBERS, $cid, $tableAccounts, $tableEmail)],
-					['query.recipients', self::parseQuery(self::QUERY_RECIPIENTS, $cid, $tableAccounts, $tableEmail)],
-					['query.emails', self::parseQuery(self::QUERY_EMAILS, $cid, $tableAccounts, $tableEmail)],
-					['query.verify', self::parseQuery(self::QUERY_VERIFY, $cid, $tableAccounts, $tableEmail)],
-					['query.expand', self::parseQuery(self::QUERY_EXPAND, $cid, $tableAccounts, $tableEmail)],
-					['query.domains', self::parseQuery(self::QUERY_DOMAINS, $cid, $tableAccounts, $tableEmail)]
+					['query.name', $this->queryName($cid)],
+					['query.members', $this->queryMembers()],
+					['query.recipients', $this->queryRecipients()],
+					['query.emails', $this->queryEmails()],
+					['query.verify', $this->queryVerify()],
+					['query.expand', $this->queryExpand()],
+					['query.domains', $this->queryDomains()],
 				],
 			],
 			[
@@ -144,15 +54,15 @@ public function getStalwartConfig(string $cid): string {
 				'prefix' => 'directory.' . $cid,
 				'type' => 'Insert',
 				'values' => [
-					[ 'type', 'sql' ],
-					[ 'store', $cid ],
-					[ 'columns.class', 'type' ],
-					[ 'columns.description', 'display_name' ],
-					[ 'columns.secret', 'password' ],
-					[ 'columns.quota', 'quota' ],
-					[ 'cache.entries', '500' ],
-					[ 'cache.ttl.positive', '1h' ],
-					[ 'cache.ttl.negative', '10m' ],
+					['type', 'sql'],
+					['store', $cid],
+					['columns.class', AccountEntity::COL_TYPE],
+					['columns.description', AccountEntity::COL_DISPLAY],
+					['columns.secret', AccountEntity::COL_PASSWORD],
+					['columns.quota', AccountEntity::COL_QUOTA],
+					['cache.entries', '500'],
+					['cache.ttl.positive', '1h'],
+					['cache.ttl.negative', '10m'],
 				],
 			],
 			[
@@ -160,16 +70,9 @@ public function getStalwartConfig(string $cid): string {
 				'prefix' => null,
 				'type' => 'Insert',
 				'values' => [
-					[ 'storage.directory', $cid ],
+					['storage.directory', $cid],
 				],
 			],
 		], JSON_THROW_ON_ERROR);
 	}
-
-	private static function parseQuery(string $query, string $cid, string $tableUsers, string $tableAlias): string {
-		$query = str_replace("\n", ' ', $query);
-		$query = str_replace('oc_stalwart_accounts', $tableUsers, $query);
-		$query = str_replace('oc_stalwart_aliases', $tableAlias, $query);
-		return str_replace(':cid', $cid, $query);
-	}
 }