diff --git a/.github/workflows/sql-test-and-build-workflow.yml b/.github/workflows/sql-test-and-build-workflow.yml
index ccc7f11d605..18b0cdfc232 100644
--- a/.github/workflows/sql-test-and-build-workflow.yml
+++ b/.github/workflows/sql-test-and-build-workflow.yml
@@ -106,7 +106,7 @@ jobs:
       - name: Build and Test
         run: |
           if [ "${{ matrix.test-type }}" = "unit" ]; then
-            ./gradlew --continue build -x spotlessCheck -x integTest -x tracingIntegTest -x yamlRestTest -x doctest
+            ./gradlew --continue build jacocoAggregatedReport -x spotlessCheck -x integTest -x tracingIntegTest -x yamlRestTest -x doctest
           elif [ "${{ matrix.test-type }}" = "integration" ]; then
             ./gradlew --continue integTest tracingIntegTest yamlRestTest
           else
@@ -124,7 +124,7 @@ jobs:
         uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4
         with:
           name: jacoco-coverage-reports
-          path: '**/build/reports/jacoco/test/jacocoTestReport.xml'
+          path: build/reports/jacoco/jacocoAggregatedReport/jacocoAggregatedReport.xml
           retention-days: 1
           if-no-files-found: error
 
diff --git a/DEVELOPER_GUIDE.rst b/DEVELOPER_GUIDE.rst
index a179b1fc64d..4c75cfdeaa7 100644
--- a/DEVELOPER_GUIDE.rst
+++ b/DEVELOPER_GUIDE.rst
@@ -243,6 +243,8 @@ For faster local iterations, skip integration tests. ``./gradlew build -x integT
      - Compile all Java source files.
    * - ./gradlew test
      - Run all unit tests.
+   * - ./gradlew test jacocoAggregatedReport
+     - Run all unit tests and generate a code coverage report across all modules in build/reports/jacoco/jacocoAggregatedReport.
    * - ./gradlew :integ-test:integTest
      - Run all integration test (this takes time).
    * - ./gradlew :integ-test:yamlRestTest
@@ -357,7 +359,7 @@ Here is a sample for integration test for your reference:
        }
    }
 
-Finally thanks to JaCoCo library, you can check out the test coverage in ``<module_name>/build/reports/jacoco`` for your changes easily.
+Finally thanks to JaCoCo library, you can check out the test coverage in ``<module_name>/build/reports/jacoco`` for your changes easily. A module's report only counts the tests of that module. To also count tests in other modules (for example ``ppl`` tests of ``core`` classes), which is the coverage that Codecov reports, run ``./gradlew test jacocoAggregatedReport`` and open ``build/reports/jacoco/jacocoAggregatedReport/html/index.html``.
 
 Deploying Locally
 -----------------
diff --git a/build.gradle b/build.gradle
index 348ff34563b..be38845404d 100644
--- a/build.gradle
+++ b/build.gradle
@@ -300,6 +300,56 @@ jacocoTestCoverageVerification {
 }
 check.dependsOn jacocoTestCoverageVerification
 
+// Each module's jacocoTestReport credits a class only with the tests of its own module, but many
+// classes are mostly tested from other modules (for example core's CalciteRelNodeVisitor is tested
+// by ppl's CalcitePPL*Test). This report merges the unit test execution data of every module that
+// applies jacoco and reports it against the classes of the modules below, with the same excludes as
+// their own jacocoTestReport. CI uploads it to Codecov. The per-module
+// jacocoTestCoverageVerification rules still measure each module's own tests only.
+def aggregatedCoverageModules = [
+        ':api',
+        ':async-query',
+        ':async-query-core',
+        ':core',
+        ':datasources',
+        ':direct-query',
+        ':direct-query-core',
+        ':opensearch',
+        ':ppl',
+        ':prometheus',
+        ':protocol',
+        ':sql',
+]
+def jacocoAggregatedReport = tasks.register('jacocoAggregatedReport', JacocoReport) {
+    group = 'verification'
+    description = 'Generates a code coverage report of all modules from the unit tests of all modules. ' +
+            'Does not run the tests; use ./gradlew test jacocoAggregatedReport.'
+    reports {
+        html.required = true
+        xml.required = true
+        csv.required = false
+    }
+}
+// The module reports set their excludes in afterEvaluate, so read them once every project is evaluated.
+gradle.projectsEvaluated {
+    jacocoAggregatedReport.configure {
+        subprojects.findAll { it.plugins.hasPlugin('jacoco') }.each { p ->
+            // 'junit4' is the JUnit 4 test task of async-query, direct-query and direct-query-core.
+            p.tasks.withType(Test).matching { it.name in ['test', 'junit4'] }.each { testTask ->
+                // Like each module's jacocoTestReport, only run after the tests rather than depend on
+                // them, so that a failing test still leaves a report for CI to upload.
+                mustRunAfter testTask
+                executionData testTask
+            }
+        }
+        aggregatedCoverageModules.each { path ->
+            def moduleReport = project(path).tasks.named('jacocoTestReport', JacocoReport).get()
+            classDirectories.from(moduleReport.classDirectories)
+            sourceDirectories.from(moduleReport.sourceDirectories)
+        }
+    }
+}
+
 
 configurations.all {
     resolutionStrategy.force 'junit:junit:4.13.2'