betodealmeida edited a comment on issue #13491:
URL: https://github.com/apache/superset/issues/13491#issuecomment-791845156
> **[Topic 2]** Most critically, with the current Superset codebase (as of
apache-superset v.1.0.1) an error occurs when attempting to perform a simple
SELECT query in the SQL Lab; see Figure 1 below. Namely, observe in Figure 1
the "Syntax Error: expected something between the word '<table_Name>' and the
'LIMIT' keyword". The root cause for this error is the improper translation to
Teradata SQL of the 'LIMIT' keyword in the Superset back-end. Teradata SQL uses
the 'TOP' or 'SAMPLE' keywords instead of 'LIMIT'. Observe that issue #11405
appears to be closely related to this issue.
This is an easy fix:
```python
class TeradataEngineSpec(BaseEngineSpec):
"""Dialect for Teradata DB."""
limit_method = LimitMethod.FETCH_MANY
...
```
This error happens because in SQL Lab we try to limit the query to prevent
fetching too much data. There are 3 strategies for this:
1. `WRAP_SQL`: if the dropdown limit is 1000, wrap the SQL Lab query and
apply a limit to the outer select:
```sql
SELECT * FROM (
$SQL_QUERY
) LIMIT 1000;
```
This method is great because it doesn't require parsing the SQL query, and
is mostly foolproof. Not all databases support this, though.
2. `FORCE_LIMIT`: parse the SQL Lab query and insert a LIMIT or replace the
existing LIMIT if present. This method is more error-prone, since it requires
parsing the original query. And as you saw, not all databases support the
`LIMIT` clause.
3. `FETCH_MANY`: do not modify the SQL query, but fetch only a limited
number of rows. With this method, the SQL Lab query is run as is, and we fetch
a number of rows equal to the limit dropdown. This is the least efficient
method, since the query might produce 1 million rows for us to fetch only 1000.
Firebird uses this.
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