Repository: dbt-labs/dbt-core

Issue:
run_sql command via dbt rpc returns Object of type Decimal is not JSON serializable
### Describe the bug
Executing a `run_sql` command via `dbt rbc` against a BigQuery profile returns `Object of type Decimal is not JSON serializable`. The equivalent command against Redshift, Snowflake, and PostgreSQL connections works correctly.

### Steps To Reproduce
A model exists with the body `with source as ( select * from {{source('recharge', 'orders')}} ) select * from source`. 

The query of the model is wrapped in a CTE limiting its results to 100 records:
```
with run_cte as (with source as ( select * from {{source('recharge', 'orders')}} )) select * from run_cte limit 100
```

And converted to base64:

```
d2l0aCBydW5fY3RlIGFzICh3aXRoIHNvdXJjZSBhcyAoIHNlbGVjdCAqIGZyb20ge3tzb3VyY2UoJ3JlY2hhcmdlJywgJ29yZGVycycpfX0gKSkgc2VsZWN0ICogZnJvbSBydW5fY3RlIGxpbWl0IDEwMA==
```

A request is made to the RPC Server with the `run_sql` command, with the following body:

```
{
    jsonrpc: "2.0",
    method: 'run_sql',
    id: 123,
    params:  {
      name: "query",
      timeout: 60,
      sql: d2l0aCBydW5fY3RlIGFzICh3aXRoIHNvdXJjZSBhcyAoIHNlbGVjdCAqIGZyb20ge3tzb3VyY2UoJ3JlY2hhcmdlJywgJ29yZGVycycpfX0gKSkgc2VsZWN0ICogZnJvbSBydW5fY3RlIGxpbWl0IDEwMA==
    }
```

### Expected behavior
I would expect this to return the result set of the underlying sql statement.

### Screenshots and log output
If applicable, add screenshots or log output to help explain your problem.

### System information
**Which database are you using dbt with?**
- [ ] postgres
- [ ] redshift
- [x] bigquery
- [ ] snowflake
- [ ] other (specify: ____________)


**The output of `dbt --version`:**
```
0.16.01
```

**The operating system you're using:** macOS 10.13.6

**The output of `python --version`:** 3.7

### Additional context
Add any other context about the problem here.



Discussion:
Thanks for the report @brettgriffin - this error occurs if a `numeric` column is found inside of a struct or array column in BigQuery

Resolving patch:
diff --git a/core/dbt/clients/agate_helper.py b/core/dbt/clients/agate_helper.py
--- a/core/dbt/clients/agate_helper.py
+++ b/core/dbt/clients/agate_helper.py
@@ -4,6 +4,7 @@
 import datetime
 import isodate
 import json
+import dbt.utils
 from typing import Iterable, List, Dict, Union, Optional, Any
 
 from dbt.exceptions import RuntimeException
@@ -92,7 +93,7 @@ def table_from_data_flat(data, column_names: Iterable[str]) -> agate.Table:
         row = []
         for value in list(_row.values()):
             if isinstance(value, (dict, list, tuple)):
-                row.append(json.dumps(value))
+                row.append(json.dumps(value, cls=dbt.utils.JSONEncoder))
             else:
                 row.append(value)
         rows.append(row)


Test patch:
diff --git a/test/integration/022_bigquery_test/test_bigquery_repeated_records.py b/test/integration/022_bigquery_test/test_bigquery_repeated_records.py
--- a/test/integration/022_bigquery_test/test_bigquery_repeated_records.py
+++ b/test/integration/022_bigquery_test/test_bigquery_repeated_records.py
@@ -26,8 +26,8 @@ def test__bigquery_fetch_nested_records(self):
             cast('Stonebreaker' as string) as lname
           ) as user,
           [
-            struct(1 as val_1, 2 as val_2),
-            struct(3 as val_1, 4 as val_2)
+            struct(1 as val_1, cast(2.12 as numeric) as val_2),
+            struct(3 as val_1, cast(4.83 as numeric) as val_2)
           ] as val
 
         union all
@@ -38,8 +38,8 @@ def test__bigquery_fetch_nested_records(self):
             cast('Brickmaker' as string) as lname
           ) as user,
           [
-            struct(7 as val_1, 8 as val_2),
-            struct(9 as val_1, 0 as val_2)
+            struct(7 as val_1, cast(8 as numeric) as val_2),
+            struct(9 as val_1, cast(null as numeric) as val_2)
           ] as val
         """
 
@@ -54,8 +54,8 @@ def test__bigquery_fetch_nested_records(self):
                 '{"fname": "Johnny", "lname": "Brickmaker"}'
             ],
             "val": [
-                '[{"val_1": 1, "val_2": 2}, {"val_1": 3, "val_2": 4}]',
-                '[{"val_1": 7, "val_2": 8}, {"val_1": 9, "val_2": 0}]'
+                '[{"val_1": 1, "val_2": 2.12}, {"val_1": 3, "val_2": 4.83}]',
+                '[{"val_1": 7, "val_2": 8}, {"val_1": 9, "val_2": null}]'
             ]
         }