add sample code for query tags with both session and statement level

Author: jiabin-hu

examples/query_tags.js

@@ -0,0 +1,59 @@
+const { DBSQLClient } = require('..');
+
+const client = new DBSQLClient();
+
+const host = process.env.DATABRICKS_HOST;
+const path = process.env.DATABRICKS_HTTP_PATH;
+const token = process.env.DATABRICKS_TOKEN;
+
+client
+  .connect({ host, path, token })
+  .then(async (client) => {
+    // Session-level query tags: applied to every statement run on this session
+    // (serialized into the session's QUERY_TAGS configuration).
+    const session = await client.openSession({
+      queryTags: {
+        team: 'engineering',
+        env: 'dev',
+        driver: 'node',
+      },
+    });
+
+    // Statement A: inherits session-level tags only.
+    const opA = await session.executeStatement('SELECT 1 AS inherits_session_tags');
+    console.log(await opA.fetchAll());
+    await opA.close();
+
+    // Statement B: statement-level query tags via executeStatement options.
+    // These are passed via confOverlay as "query_tags" and apply ONLY to this statement.
+    // Note: `env` here overrides the session-level `env: 'dev'` — for this statement
+    // it will be `env: 'prod'`. Subsequent statements without statement-level tags
+    // revert to the session-level values.
+    const opB = await session.executeStatement('SELECT 2 AS has_statement_tags', {
+      queryTags: {
+        env: 'prod',
+        request_id: 'abc-123',
+        feature: 'reporting',
+      },
+    });
+    console.log(await opB.fetchAll());
+    await opB.close();
+
+    // Statement C: demonstrates escaping of special characters (`\`, `:`, `,`)
+    // in tag values, plus null/undefined values which serialize as bare keys.
+    const opC = await session.executeStatement('SELECT 3 AS escaped_and_null_tags', {
+      queryTags: {
+        path: 'C:\\users\\me',
+        note: 'hello, world',
+        flag: null,
+      },
+    });
+    console.log(await opC.fetchAll());
+    await opC.close();
+
+    await session.close();
+    await client.close();
+  })
+  .catch((error) => {
+    console.log(error);
+  });