fix(agents): sanitize backtick identifier quote for GBase 8s

agents/common/src/main/java/com/dbx/agent/AbstractJdbcAgent.java

@@ -454,7 +454,57 @@ public abstract class AbstractJdbcAgent extends BaseDatabaseAgent {
         }
         try {
             String quote = connection.getMetaData().getIdentifierQuoteString();
-            return quote == null || quote.trim().isEmpty() ? "" : quote.trim();
+            if (quote == null || quote.trim().isEmpty()) {
+                return "";
+            }
+            return sanitizeInformixFamilyBacktickQuote(params, connection, quote.trim());
+        } catch (Exception ignored) {
+            return "";
+        }
+    }
+
+    // GBase 8s and other Informix-family JDBC drivers report "`" from
+    // getIdentifierQuoteString() even though their servers reject backtick-quoted
+    // identifiers with "illegal character in statement" outside MySQL compatibility
+    // mode (SQLMODE=mysql). An empty quote makes clients emit unquoted identifiers,
+    // which both SQL modes accept.
+    private static String sanitizeInformixFamilyBacktickQuote(ConnectParams params, Connection connection, String quote) {
+        if (!"`".equals(quote) || !isInformixFamilyJdbc(params, connection) || isInformixFamilyMysqlCompat(params, connection)) {
+            return quote;
+        }
+        return "";
+    }
+
+    private static boolean isInformixFamilyJdbc(ConnectParams params, Connection connection) {
+        StringBuilder identity = new StringBuilder();
+        appendJdbcIdentity(identity, params.getConnection_string());
+        appendJdbcIdentity(identity, params.getJdbc_driver_class());
+        List<String> driverPaths = params.getJdbc_driver_paths();
+        if (driverPaths != null) {
+            for (String path : driverPaths) {
+                appendJdbcIdentity(identity, path);
+            }
+        }
+        appendJdbcIdentity(identity, connectionUrl(connection));
+        String normalized = identity.toString().toLowerCase(Locale.ROOT);
+        return normalized.contains("jdbc:gbasedbt")
+            || normalized.contains("jdbc:informix")
+            || normalized.contains("com.gbasedbt")
+            || normalized.contains("com.informix");
+    }
+
+    private static boolean isInformixFamilyMysqlCompat(ConnectParams params, Connection connection) {
+        if (params.isMysql_compat_mode()) {
+            return true;
+        }
+        String identity = (params.getConnection_string() + "\n" + connectionUrl(connection)).toLowerCase(Locale.ROOT);
+        return identity.contains("sqlmode=mysql");
+    }
+
+    private static String connectionUrl(Connection connection) {
+        try {
+            String url = connection.getMetaData().getURL();
+            return url == null ? "" : url;
         } catch (Exception ignored) {
             return "";
         }

agents/common/src/test/java/com/dbx/agent/AbstractJdbcAgentTest.java

@@ -115,6 +115,55 @@ class AbstractJdbcAgentTest {
         assertEquals(0, tracking.compatibilityQueryCount);
     }
 
+    @Test
+    void ignoresGbase8sDriverBacktickIdentifierQuote() {
+        TrackingConnection tracking = new TrackingConnection();
+        tracking.identifierQuote = "`";
+        tracking.jdbcUrl = "jdbc:gbasedbt-sqli://localhost:9088/appdb:GBASEDBTSERVER=gbase8s";
+        TestAgent agent = new TestAgent(tracking);
+
+        agent.connect(new ConnectParams());
+
+        assertEquals("", agent.getIdentifierQuote());
+    }
+
+    @Test
+    void ignoresBacktickQuoteForInformixFamilyConnectionString() {
+        TrackingConnection tracking = new TrackingConnection();
+        tracking.identifierQuote = "`";
+        TestAgent agent = new TestAgent(tracking);
+
+        ConnectParams params = new ConnectParams();
+        params.setConnection_string("jdbc:informix-sqli://localhost:9088/appdb:INFORMIXSERVER=ol_informix");
+        agent.connect(params);
+
+        assertEquals("", agent.getIdentifierQuote());
+    }
+
+    @Test
+    void keepsInformixFamilyBacktickQuoteInMysqlCompatMode() {
+        TrackingConnection tracking = new TrackingConnection();
+        tracking.identifierQuote = "`";
+        tracking.jdbcUrl = "jdbc:gbasedbt-sqli://localhost:9088/appdb:GBASEDBTSERVER=gbase8s;SQLMODE=mysql";
+        TestAgent agent = new TestAgent(tracking);
+
+        agent.connect(new ConnectParams());
+
+        assertEquals("`", agent.getIdentifierQuote());
+    }
+
+    @Test
+    void keepsNonBacktickQuotesForInformixFamilyDrivers() {
+        TrackingConnection tracking = new TrackingConnection();
+        tracking.identifierQuote = "\"";
+        tracking.jdbcUrl = "jdbc:gbasedbt-sqli://localhost:9088/appdb:GBASEDBTSERVER=gbase8s";
+        TestAgent agent = new TestAgent(tracking);
+
+        agent.connect(new ConnectParams());
+
+        assertEquals("\"", agent.getIdentifierQuote());
+    }
+
     @Test
     void testsConnectionsThroughSharedLifecycle() {
         TrackingConnection tracking = new TrackingConnection();
@@ -469,6 +518,7 @@ class AbstractJdbcAgentTest {
         private boolean autoCommit = true;
         private String compatibilityMode;
         private String identifierQuote = "\"";
+        private String jdbcUrl;
         private boolean compatibilityQueryFails;
         private int compatibilityQueryCount;
         private boolean isValidUnsupported;
@@ -534,6 +584,9 @@ class AbstractJdbcAgentTest {
                     if ("getIdentifierQuoteString".equals(method.getName())) {
                         return identifierQuote;
                     }
+                    if ("getURL".equals(method.getName())) {
+                        return jdbcUrl;
+                    }
                     return defaultValue(method.getReturnType());
                 }
             });