Skip subsequent steps if there are no schema changes

.github/workflows/compare.yaml

@@ -35,16 +35,24 @@ jobs:
         run: |
           echo "Checking for changes compared with: ${{ github.event.pull_request.base.ref }}"
           CHANGED_FILES=$(git diff --name-only origin/${{ github.event.pull_request.base.ref }}..HEAD -- ${{ env.SCHEMA_DIR }} | grep '\.yaml$')
-          CHANGED_FILES=$(echo "$CHANGED_FILES" | sed "s|^${{ env.SCHEMA_DIR }}/||" | tr '\n' ' ')
-          echo "CHANGED_FILES=$CHANGED_FILES" >> $GITHUB_ENV
+          if [ -z "$CHANGED_FILES" ]; then
+            echo "No schema files changed."
+            echo "schema_files_changed=false" >> $GITHUB_ENV
+          else
+            CHANGED_FILES=$(echo "$CHANGED_FILES" | sed "s|^${{ env.SCHEMA_DIR }}/||" | tr '\n' ' ')
+            echo "CHANGED_FILES=$CHANGED_FILES" >> $GITHUB_ENV
+            echo "schema_files_changed=true" >> $GITHUB_ENV
+          fi
 
       - name: Check out PR base ref
+        if: env.schema_files_changed == 'true'
         uses: actions/checkout@v4
         with:
           ref: ${{ github.event.pull_request.base.ref }}
           path: base-ref
 
       - name: Run deepdiff comparison
+        if: env.schema_files_changed == 'true'
         run: |
           for file in ${{ env.CHANGED_FILES }}; do
             echo "Comparing $file..."
@@ -54,6 +62,7 @@ jobs:
           done
 
       - name: Run alembic comparison
+        if: env.schema_files_changed == 'true'
         run: |
           for file in ${{ env.CHANGED_FILES }}; do
             echo "Comparing $file..."
@@ -63,6 +72,7 @@ jobs:
           done
 
       - name: Run alembic comparison on deployed schemas
+        if: env.schema_files_changed == 'true'
         run: |
           ERROR_FLAG=0
           DEPLOYED_SCHEMAS=$(cat current-ref/yml/deployed-schemas.txt)