truncate if exists (#250)

Author: javier

documentation/reference/sql/drop.md

@@ -20,7 +20,8 @@ permanently deletes all tables, all materialized views, and their contents on di
 ### IF EXISTS
 
 An optional `IF EXISTS` clause may be added directly after the `DROP TABLE`
-keywords to indicate that the selected table should be dropped if it exists.
+keywords to indicate that the selected table should be dropped only if it exists.
+Without `IF EXISTS`, QuestDB will throw an error if the table does not exist.
 
 ## Description
 

documentation/reference/sql/truncate.md

@@ -11,6 +11,12 @@ the table itself.
 
 ![Flow chart showing the syntax of the TRUNCATE TABLE keyword](/images/docs/diagrams/truncateTable.svg)
 
+### IF EXISTS
+
+An optional `IF EXISTS` clause may be added directly after the `TRUNCATE TABLE`
+keywords to indicate that the selected table should be truncated only if it exists.
+Without `IF EXISTS`, QuestDB will throw an error if the table does not exist.
+
 ## Notes
 
 This command irremediably deletes the data in the target table. In doubt, make
@@ -19,9 +25,14 @@ sure you have created [backups](/docs/operations/backup/) of your data.
 ## Examples
 
 ```questdb-sql
-TRUNCATE TABLE ratings;
+TRUNCATE TABLE trades;
 ```
 
+This example will not throw an error, even if the table does not exist:
+
+```questdb-sql
+TRUNCATE TABLE IF EXISTS trades_non_existent;
+```
 ## See also
 
 To delete both the data and the table structure, use

static/images/docs/diagrams/.railroad

@@ -349,7 +349,7 @@ show
   )
 
 truncateTable
-  ::= 'TRUNCATE TABLE' tableName ';'
+  ::= 'TRUNCATE TABLE' ('IF' 'EXISTS')? tableName ';'
 
 explain
   ::= 'EXPLAIN' statement