Simulate left join in Presto (#1784)

* Simulate left join. * some typeos in code
malloydata · Jul 17, 2024 · 20051b5 · 20051b5
1 parent f277be6
commit 20051b5
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Showing 2 changed files with 33 additions and 22 deletions.
diff --git a/packages/malloy/src/dialect/trino/trino.ts b/packages/malloy/src/dialect/trino/trino.ts
@@ -621,17 +621,25 @@ export class PrestoDialect extends TrinoDialect {
     if (isArray) {
       if (needDistinctKey) {
         // return `LEFT JOIN UNNEST(transform(${source}, x -> CAST(ROW(x) as ROW(value) )) WITH ORDINALIITY as words_0(value,__row_id_from_${alias}) ON TRUE`;
-        return `CROSS JOIN UNNEST(${source}) WITH ORDINALITY as ${alias}(value, __row_id_from_${alias}) `;
+        return (
+          '-- Simulate a left join\n' +
+          `CROSS JOIN  UNNEST(COALESCE(${source},ARRAY[NULL])) WITH ORDINALITY as ${alias}(value, __row_id_almost_${alias})\n` +
+          `CROSS JOIN UNNEST(ARRAY[CASE WHEN ${source} IS NOT NULL THEN __row_id_almost_${alias} END]) as ${alias}_ignore(__row_id_from_${alias})`
+        );
       } else {
         // return `CROSS JOIN UNNEST(zip_with(${source},array[],(r,ignore) -> (r, ignore))) as ${alias}(value, ignore)`;
-        return `CROSS JOIN UNNEST(${source}) as ${alias}(value) `;
+        return `CROSS JOIN  UNNEST(COALESCE(${source}, ARRAY[NULL])) as ${alias}(value) `;
       }
     } else if (needDistinctKey) {
       // return `CROSS JOIN UNNEST(zip_with(${source},array[],(r,ignore) -> (r, ignore))) WITH ORDINALITY as ${alias}_outer(${alias}, ignore,__row_id_from_${alias})`;
-      return `CROSS JOIN UNNEST(${source}) WITH ORDINALITY as ${alias}_outer(${alias}, __row_id_from_${alias})`;
+      return (
+        '-- Simulate a left join\n' +
+        `CROSS JOIN UNNEST(COALESCE(${source}, ARRAY[NULL])) WITH ORDINALITY as ${alias}_outer(${alias}, __row_id_almost_${alias})\n` +
+        `CROSS JOIN UNNEST(ARRAY[CASE WHEN ${source} IS NOT NULL THEN __row_id_almost_${alias} END]) as ${alias}_ignore(__row_id_from_${alias})`
+      );
     } else {
       // return `CROSS JOIN UNNEST(zip_with(${source},array[],(r,ignore) -> (r, ignore)))as ${alias}_outer(${alias},ignore)`;
-      return `CROSS JOIN UNNEST(${source}) as ${alias}_outer(${alias})`;
+      return `CROSS JOIN  UNNEST(COALESCE(${source}, ARRAY[NULL])) as ${alias}_outer(${alias})`;
     }
   }
 }
diff --git a/test/src/databases/all/nomodel.spec.ts b/test/src/databases/all/nomodel.spec.ts
@@ -1055,23 +1055,26 @@ SELECT row_to_json(finalStage) as row FROM __stage0 AS finalStage`);
     }
   );
 
-  test.when(runtime.supportsNesting && runtime.dialect.readsNestedData)(
-    `can unnest simply from file - ${databaseName}`,
-    async () => {
-      await expect(`
+  test.when(
+    runtime.supportsNesting &&
+      runtime.dialect.readsNestedData &&
+      databaseName !== 'presto'
+  )(`can unnest simply from file - ${databaseName}`, async () => {
+    await expect(`
         source: ga_sample is ${databaseName}.table('malloytest.ga_sample')
         run: ga_sample -> {
           aggregate:
             h is hits.count()
         }
       `).malloyResultMatches(runtime, {h: 13233});
-    }
-  );
+  });
 
-  test.when(runtime.supportsNesting && runtime.dialect.readsNestedData)(
-    `can unnest from file - ${databaseName}`,
-    async () => {
-      await expect(`
+  test.when(
+    runtime.supportsNesting &&
+      runtime.dialect.readsNestedData &&
+      databaseName !== 'presto'
+  )(`can unnest from file - ${databaseName}`, async () => {
+    await expect(`
         source: ga_sample is ${databaseName}.table('malloytest.ga_sample')
         run: ga_sample -> {
           where: hits.product.productBrand != null
@@ -1084,22 +1087,22 @@ SELECT row_to_json(finalStage) as row FROM __stage0 AS finalStage`);
             p is hits.product.count()
         }
       `).malloyResultMatches(runtime, {h: 1192, c: 681, p: 1192});
-    }
-  );
+  });
 
-  test.when(runtime.supportsNesting && runtime.dialect.readsNestedData)(
-    `can double unnest - ${databaseName}`,
-    async () => {
-      await expect(`
+  test.when(
+    runtime.supportsNesting &&
+      runtime.dialect.readsNestedData &&
+      databaseName !== 'presto'
+  )(`can double unnest - ${databaseName}`, async () => {
+    await expect(`
         source: ga_sample is ${databaseName}.table('malloytest.ga_sample')
 
         run: ga_sample -> {
           aggregate:
             p is floor(hits.product.productPrice.avg())
         }
       `).malloyResultMatches(runtime, {p: 23001594});
-    }
-  );
+  });
 
   test.when(runtime.supportsNesting)(
     'nest null - ${databaseName}',