Github user felixcheung commented on the issue:
https://github.com/apache/zeppelin/pull/2121
To elaborate, this is what the documentation says
```
### Usage `precode`
<-- this is a new section
+You can set `precode` for each data source. Code runs once while opening
the connection.
<--- good, there's a description
+##### Properties
<-- here we start a subsection
+<table class="table-configuration">
+ <tr>
+ <th>Property Name</th>
+ <th>Value</th>
+ </tr>
+ <tr>
+ <td>default.driver</td>
+ <td>org.postgresql.Driver</td>
<-- there we have a table immediately...
<-- what is default., mysql.? why do we need this properties/table?
+ <tr>
+ <td>mysql.url</td>
+ <td>jdbc:mysql://localhost:3306/</td>
+ <tr>
+ <td>mysql.precode</td>
+ <td>set @v=12</td>
+ </tr>
+</table>
+
+##### Usage
+```sql
+%jdbc(mysql)
+select @v
<-- can we say here we get in return v, which is set in the precode
```
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