fix(sqllab): table preview has gone (apache#25977)

(cherry picked from commit cdbbd83)

superset-frontend/src/components/DatabaseSelector/DatabaseSelector.test.tsx

@@ -290,7 +290,13 @@ test('Sends the correct db when changing the database', async () => {
 
 test('Sends the correct schema when changing the schema', async () => {
   const props = createProps();
-  render(<DatabaseSelector {...props} />, { useRedux: true, store });
+  const { rerender } = render(<DatabaseSelector {...props} db={null} />, {
+    useRedux: true,
+    store,
+  });
+  await waitFor(() => expect(fetchMock.calls(databaseApiRoute).length).toBe(1));
+  rerender(<DatabaseSelector {...props} />);
+  expect(props.onSchemaChange).toBeCalledTimes(0);
   const select = screen.getByRole('combobox', {
     name: 'Select schema or type to search schemas',
   });
@@ -301,4 +307,5 @@ test('Sends the correct schema when changing the schema', async () => {
   await waitFor(() =>
     expect(props.onSchemaChange).toHaveBeenCalledWith('information_schema'),
   );
+  expect(props.onSchemaChange).toBeCalledTimes(1);
 });

superset-frontend/src/components/DatabaseSelector/index.tsx

@@ -16,7 +16,7 @@
  * specific language governing permissions and limitations
  * under the License.
  */
-import React, { ReactNode, useState, useMemo, useEffect } from 'react';
+import React, { ReactNode, useState, useMemo, useEffect, useRef } from 'react';
 import { styled, SupersetClient, t } from '@superset-ui/core';
 import rison from 'rison';
 import { AsyncSelect, Select } from 'src/components';
@@ -133,6 +133,8 @@ export default function DatabaseSelector({
   const [currentSchema, setCurrentSchema] = useState<SchemaOption | undefined>(
     schema ? { label: schema, value: schema, title: schema } : undefined,
   );
+  const schemaRef = useRef(schema);
+  schemaRef.current = schema;
   const { addSuccessToast } = useToasts();
 
   const loadDatabases = useMemo(
@@ -215,7 +217,7 @@ export default function DatabaseSelector({
 
   function changeSchema(schema: SchemaOption | undefined) {
     setCurrentSchema(schema);
-    if (onSchemaChange) {
+    if (onSchemaChange && schema?.value !== schemaRef.current) {
       onSchemaChange(schema?.value);
     }
   }
@@ -229,7 +231,9 @@ export default function DatabaseSelector({
     onSuccess: (schemas, isFetched) => {
       if (schemas.length === 1) {
         changeSchema(schemas[0]);
-      } else if (!schemas.find(schemaOption => schema === schemaOption.value)) {
+      } else if (
+        !schemas.find(schemaOption => schemaRef.current === schemaOption.value)
+      ) {
         changeSchema(undefined);
       }